Introduction

The rapid development of antibiotic resistance among the major respiratory pathogens has created a serious problem for the effective management of respiratory tract infections.1, 2, 3, 4, 5, 6 There is a great need for new antibiotics that address the problem of antibiotic resistance. Under these circumstances, a substantial amount study has been carried out on novel macrolides. These investigations have led to the discovery of C-4″-carbamate macrolides. One of the leading C-4″-carbamates, CP-544372 (Figure 1, compound 1), has demonstrated good in vitro antibacterial activity against erythromycin-susceptible and -resistant organisms.7, 8, 9

Figure 1
figure 1

Structures of CP-544372 and A-60565.

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The study of high-resolution X-ray co-crystal structures has shown that the 3-position group of macrolides is located near G2505 and C2610, and the cladinose group of erythromycin or clarithromycin is located at and fits with the cavity formed by G2505, C2610 and C2611 in domain V of the erythromycin-binding site.9, 10, 11 The C-3 cladinose sugar attached to the 14-membered ring macrolides is believed to be responsible for the induction of macrolide resistance. This moiety also seems to be responsible for efflux resistance.12 Fernandes et al. have reported that the induction of methylase in macrolide-resistant bacteria could be dissociated from inhibition of the bacteria by using erythromycin analogs with modification at the 4″ position of the cladinose sugar.13 Some studies have reported that the introduction of certain groups to the 4″ position of the cladinose sugar results in a negligible effect on antibacterial activity. 4″ modification can alter the relative potency of an antibiotic.9, 14 Many new derivatives of macrolides for the effective management of erythromycin resistance have been investigated.13 A-60565 (Figure 1, compound 2) has lower MICs than erythromycin does against inducibly and constitutively resistant bacteria.9, 15 Compound 3 (Figure 2) has an MIC against erythromycin-susceptible and -resistant Streptococcus pneumoniae of ⩽0.02 and ⩽2 μg ml−1, respectively.16 Compound 4 (Figure 2) has potent activity against most resistant bacteria.9 Compounds 5a and 5b (Figure 3) were found to have potent activity against erythromycin-resistant S. pneumoniae encoded by the erm or mef gene.17, 18 Compounds 6a and 6b (Figure 3) are effective (0.5 and 0.5 μg ml−1) against two strains of erythromycin-resistant S. pneumoniae, whose resistance is encoded by the erm and mef gene, respectively.19

Figure 2
figure 2

Structures of compound 3 and compound 4.

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Figure 3
figure 3

Structures of compound 5 and compound 6.

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6,11-Di-O-methylerythromycin A (Figure 4, compound 7) shows excellent in vitro and in vivo antibacterial activity against Gram-positive bacteria and Mycoplasma pneumoniae.20 On the basis of the above findings, we designed novel structural 14-membered analogs of macrolide antibiotics that comprised the essential features for addressing macrolide resistance. By introduction of various amino carbonyl chain to the 4″-hydroxyl group of the 6,11-di-O-methylerythromycin A, a series of novel 4″-carbamates were obtained.

Figure 4
figure 4

Structure of 6,11-di-O-methylerythromycin A.

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Results

Chemistry

The synthetic method of 4″-carbamates of 6,11-di-O-methylerythromycin A is shown in Scheme 1. Our approach to get 4″-substituted derivatives is to regioselectively protect 2′-OH of 6,11-di-O-methylerythromycin A (7) and to modify the 4″-OH. 2′-O-acetyl 6,11-di-O-methylerythromycin A (8) provided a convenient starting material for the chemical modification leading to the 4″-substituted derivatives.

Scheme 1
figure 5

Reagents and conditions: (a) acetic anhydride, acetone, K2CO3, NaHCO3, 24h; (b) CDI, NaH, DMF, 0oC, 1 h; (c) RNH2, DMF, DBU, rt, 24h; (d) CH3OH, 55oC, 20h.

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By using the method of Baker et al.,21, 22, 23 8 was treated with excess 1,1-carbonyldiimidazole and sodium hydride in DMF at 0 °C for 1 h, 6,11-di-O-methyl-2′-O-acetyl-4″-O-acylimidazolyl erythromycin A (9) was obtained in a yield of 93%. The structure of 9 was confirmed by 13C NMR spectrum in which two carbon peaks of carbonate and carbamate could be found at δ 170.0 and δ 148.5. Compounds 10a–y were prepared by reacting compound 9 with corresponding amines and 1,8-diazabicyclo[5.4.0]undec-7-ene, followed by deprotection of the acetyl group with methanol (Scheme 1). The structures of 10a–y were determined by 13C NMR, 1H NMR, MS and IR spectra.

Antibacterial activity

All of the 4″-carbamates synthesized, as well as erythromycin, clarithromycin and azithromycin as reference compounds, were tested for in vitro antibacterial activity against three strains of Staphylococcus aureus and two strains of Streptococcus pneumoniae and Haemophilus influenzae. The activities are reported in Table 1 as MICs, which were determined by the broth microdilution method as recommended by the National Committee for Clinical Laboratory Standards.

Table 1 In vitro antibacterial activities of prepared macrolides
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To evaluate the potential antibacterial activity of each analog to overcome macrolide resistance, various macrolide-resistant strains were included: S. aureus ATCC25923: erythromycin-susceptible strain; S. aureus A265: erythromycin-resistant but methicillin-susceptible strain; S. aureus A333: erythromycin-resistant and methicillin-resistant strain; S. pneumoniae ATCC49619: erythromycin-susceptible strain; S. pneumoniae 3469: erythromycin-resistant strain; H. influenzae ATCC49247: ampicillin-susceptible strain; and H. influenzae 3300: ampicillin-resistant strain.

The results in Table 1 show the antibacterial activity of 4″-carbamates and reference compounds (erythromycin, clarithromycin and azithromycin). We presumed that chemical modification that affected the conformation would affect the ability of the antibiotics to bind to bacterial ribosomes. We obtained some new derivatives of 6,11-di-O-methylerythromycin A by modifying the 4″ OH group with various carbamate groups such as alkylcarbamoyl, hydroxy-alkylcarbamoyl, alkoxy-alkylcarbamoyl, heterocyclic-carbamoyl, substituted benzylcarbamoyl and substituted phenethylcarbamoyl. To our surprise, most of the derivatives tested had potent activity against most resistant bacteria. Among these, compounds 10u, 10v, 10w and 10y were found to have potent activity against most susceptible and resistant bacteria. In particular, compound 10y exhibited excellent antibacterial activity in comparison to others.

Discussion

A simple and efficient method for preparation of 4″-carbamates of macrolides was developed. These carbamates were evaluated for antibacterial activity against macrolide-susceptible and -resistant pathogens. To our surprise, most of the derivatives tested had potent activity against most resistant bacteria. Among these, compounds 10u, 10v, 10w and 10y were found to have potent activity against most susceptible and resistant bacteria. In particular, compound 10y showed excellent antibacterial activity in comparison to others. This study may present a major opportunity for the development of new macrolide antibiotics to combat effectively the growing problem of macrolide resistance.

The improved antibacterial activity against resistant bacteria achieved by these derivatives was possibly because the induction of methylase in macrolide-resistant bacteria could be dissociated from inhibition of the bacteria by using erythromycin analogs with modification at the 4″ position of the cladinose sugar. It is worthy of notice that 4″-modified derivatives of 14-membered macrolides are probably the effective management of macrolide resistance, and this study may present a major opportunity for the development of new macrolide antibiotics to combat the growing problem of antibiotic resistance.

Methods

General experimental procedures

Reagents were purchased from commercial sources. Solvents and reagents were dried and purified according to the literature methods. Melting points were uncorrected and measured on an XT-4 apparatus. IR spectra were recorded from KBr pellets at a range of 400–4000 cm−1 on a Spectrum One (Perkin Elmer, Shelton, CT, USA) spectrometer. 1H NMR and 13C NMR spectra were obtained on a Varian Mercury VX400 apparatus (American Varian Inc., Palo Alto, CA, USA) in CDCl3 with TMS as internal standard. The elemental analysis (C, H, N) data were obtained from a VarioEL III elemental analyzer (German Elementar. Co., Ltd, Hanau, Germany). All the ampicillin- and erythromycin-resistant strains chosen in this test are constitutively resistant strains supplied by the Ministry of Health National Antimicrobial Resistance Investigation Net (China).

6,11-Di-O-methyl-2′-O-acetylerythromycin A (8)

To a solution of 6,11-di-O-methylerythromycin A (7) (3.05 g, 4.0 mmol) in acetone (20 ml) at room temperature were added acetic anhydride (7.5 ml, 8 mmol, 2.0 equiv.) and K2CO3 (1.10 g, 8 mmol, 2.0 equiv.). The resulting solution was allowed to stir for 24 h at the same temperature. The reaction was quenched with 5% aqueous NaHCO3 (20 ml) and the aqueous layer was extracted with CH2Cl2 (3 × 20 ml). The combined organic layers were dried over anhydrous Na2SO4, filtered and concentrated in vacuum. The residue was crystallized to afford 3.03 g (94%) of 8 as a white solid: m.p. 167–170 °C; IR (KBr): 3474, 2976, 2940, 2875, 1723, 1460, 1374, 1242, 1171, 1106, 1058, 1003 cm−1; 1H NMR (400 MHz, CDCl3): δ 4.97–4.94 (m, 2H), 4.83 (m, 1H), 4.66 (m, 1H), 4.00 (m, 1H), 3.73 (d, J=5.9 Hz, 1H), 3.68 (d, J=10.1 Hz, 1H), 3.57 (s, 3H), 3.41 (s, 1H), 3.37 (s, 3H), 3.07 (s, 3H), 3.05–2.93 (m, 3H), 2.71 (m, 1H), 2.37 (s, 6H), 2.17 (m, 1H), 2.07 (s, 3H), 2.03–1.99 (s, 3H), 1.98–1.80 (m, 3H), 1.70–1.61 (m, 2H), 1.47 (m, 1H), 1.37 (s, 3H), 1.34 (m, 1H), 1.30–0.94 (m, 18H), 0.92–0.90 (m, 3H), 0.85–0.81 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.0, 174.9, 169.7, 99.4, 95.6, 79.1, 78.4, 77.8, 77.2, 77.0, 75.5, 72.4, 70.7, 67.2, 65.7, 62.2, 60.4, 49.9, 48.8, 45.1, 44.4, 39.4, 37.4, 37.3, 36.7, 34.6, 30.0, 29.8, 21.1, 21.0, 20.8, 20.0, 18.8, 18.2, 17.6, 17.1, 15.6, 12.3, 10.0, 8.7. MS (ESI) m/z calcd. for C41H73NO14 803.5; found (M+H+) 804.1.

6,11-Di-O-methyl-2′-O-acetyl-4″-O-acylimidazolyl erythromycin A (9)

To a solution of 8 (1.61 g, 2 mmol) in DMF (20 ml) were added NaH (0.096 g, 4 mmol, 2.0 equiv.) and carbonyldiimidazole (0.705 g, 4 mmol, 2.0 equiv.). The resulting solution was stirred at 0 °C for 1 h. The reaction was quenched with saturated NaHCO3 (20 ml) and the aqueous layer was extracted with CH2Cl2 (3 × 10 ml). The combined organic layers were dried over anhydrous Na2SO4, filtered and concentrated in vacuum. The residue was purified to afford 1.67 g (93%) of 9 as a white solid: m.p. 171–174 °C; IR (KBr): 3469, 2975, 2941, 1773, 1753, 1721, 1464, 1392, 1345, 1288, 1239, 1172, 1110, 1059, 1011 cm−1; 1H NMR (400 MHz, CDCl3): δ 8.07 (s, 1H), 7.38 (s, 1H), 7.11 (s, 1H), 5.06 (d, J=6.7 Hz, 1H), 4.97 (m, 1H), 4.81–4.76 (m, 3H), 4.48 (m, 1H), 3.73–3.67 (m, 2H), 3.63 (m, 1H), 3.58 (s, 3H), 3.41 (s, 3H), 3.08 (m, 1H), 3.07 (s, 3H), 3.04–2.97 (m, 2H), 2.71 (m, 1H), 2.58 (m, 1H), 2.49 (d, J=15.2 Hz, 1H), 2.30 (s, 6H), 2.17 (m, 1H), 2.06 (s, 3H), 2.03 (m, 1H), 1.94–1.86 (m, 3H), 1.78–1.68 (m, 4H), 1.53 (m, 1H), 1.50 (m, 1H), 1.35 (s, 3H), 1.32 (m, 1H), 1.26–1.23 (m, 9H), 1.16–1.10 (m, 6H), 1.05–0.99 (m, 6H), 0.87–0.84 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.4, 175.2, 170.0, 148.5, 136.8, 130.9, 116.9, 99.9, 96.0, 82.9, 79.5, 78.8, 78.5, 76.0, 72.6, 71.7, 67.9, 67.5, 63.5, 63.1, 60.8, 50.3, 49.4, 45.6, 44.7, 40.7, 37.7, 37.6, 37.0, 35.2, 30.5, 29.6, 25.6, 21.5, 21.3, 21.1, 20.3, 19.3, 18.3, 17.6, 16.1, 12.8, 10.4, 9.2. MS (ESI) m/z calcd. for C45H75N3O15 897.52; found (M+H+) 898.0.

General methods for 4″-carbamates of 6,11-di-O-methylerythromycin A 10(a–y)

To a solution of 9 (1.35 g, 1.50 mmol) in DMF (15 ml) at 0 °C were added 1,8-diazabicyclo[5.4.0]undec-7-ene (0.33 ml, 2.25 mmol, 1.5 equiv.) and corresponding amine (2.25 mmol, 1.5 equiv.). The resulting solution was raised to room temperature and stirred for 24 h at the same temperature. The reaction was quenched with water (30 ml) and the aqueous layer was extracted with ethyl acetate (315 ml). The combined organic layers were washed with brine, and dried over anhydrous Na2SO4, filtered. The filtrate was concentrated in vacuum to afford a crude product.

A solution of the above crude product in methanol (15 ml) was heated to 55 °C and stirred for 20 h at the same temperature. After concentrating the reaction solution in vacuum, the residue was purified by chromatography to afford products 10(a–y).

6,11-Di-O-methyl-4″-O-(N-propylcarbamoyl)erythromycin A (10a)

White solid, yield 86.1%, m.p. 216–220 °C; IR (KBr): 3350, 2974, 2931, 1732, 1715, 1539, 1457, 1380, 1265, 1164, 1109, 1091, 1039, 1007 cm−1; 1H NMR (400 MHz, CDCl3): δ 4.97 (d, J=6.7 Hz, 2H), 4.72 (d, J=8.3 Hz, 1H), 4.54–4.49 (m, 2H), 4.30 (m, 1H), 3.75 (d, J=6.4 Hz, 1H), 3.71–3.65 (m, 2H), 3.57 (s, 3H), 3.50 (m, 1H), 3.43 (s, 1H), 3.32 (s, 3H), 3.20 (m, 1H), 3.09 (s, 3H), 3.07–3.04 (m, 2H), 2.98 (m, 1H), 2.62–2.53 (m, 2H), 2.43 (d, J=15.2 Hz, 1H), 2.30 (s, 6H), 2.06–2.03 (m, 2H), 1.95–1.85 (m, 3H), 1.82–1.59 (m, 6H), 1.51–1.46 (m, 1H), 1.38 (s, 3H), 1.33–1.30 (m, 2H), 1.26–1.08 (m, 23H), 0.84–0.80 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.5, 175.6, 155.4, 102.1, 96.5, 79.4, 78.9, 78.6, 77.7, 76.0, 72.9, 71.2, 67.8, 65.0, 63.5, 60.8, 50.6, 49.9, 49.6, 45.6, 44.7, 40.2, 38.0, 37.9, 37.7, 35.3, 33.2, 28.8, 25.4, 24.7, 21.8, 21.5, 20.9, 20.3, 19.4, 18.4, 17.4, 16.0, 12.8, 10.5, 9.3; MS (ESI) m/z calcd. for C43H78N2O14 846.55; found (M+H+) 847.1; Anal. calcd. (%) for C43H78N2O14: C 60.97, H 9.28, N 3.31; found: C 60.95, H 9.25, N 3.34.

6,11-Di-O-methyl-4″-O-(N-butylcarbamoyl)erythromycin A (10b)

White solid, yield 76.3%, m.p. 202–206 °C; IR (KBr): 3470, 2973, 2936, 1729, 1715, 1458, 1376, 1342, 1170, 1092, 1053, 1011 cm−1; 1H NMR (400 MHz, CDCl3): δ 4.98 (d, J=8.2 Hz, 2H), 4.79 (m, 1H), 4.56–4.52 (m, 2H), 4.30 (m, 1H), 3.75 (d, J=6.6 Hz, 1H), 3.72–3.70 (m, 2H), 3.59 (s, 3H), 3.44 (s, 1H), 3.32 (s, 3H), 3.27–3.17 (m, 2H), 3.10 (s, 3H), 3.06–3.03 (m, 2H), 2.99 (m, 1H), 2.63–2.57 (m, 2H), 2.43 (d, J=14.4 Hz, 1H), 2.31 (s, 6H), 2.06 (m, 1H), 1.90–1.64 (m, 12H), 1.52–1.39 (m, 1H), 1.37 (s, 3H), 1.35–1.33 (m, 2H), 1.32–1.09 (m, 20H), 0.93–0.88 (m, 3H), 0.85–0.81 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.5, 175.6, 156.3, 102.1, 96.5, 79.5, 79.0, 78.7, 78.6, 77.7, 76.0, 73.0, 71.2, 67.8, 65.0, 63.5, 60.8, 50.6, 49.5, 45.5, 44.8, 40.8, 38.0, 37.9, 37.7, 35.4, 32.0, 29.7, 28.9, 21.7, 21.5, 20.9, 20.3, 19.8, 19.4, 18.3, 17.4, 16.0, 13.7, 12.8, 10.2, 9.3; MS (ESI) m/z calcd. for C44H80N2O14 860.56; found (M+H+) 861.1; Anal. calcd. (%) for C44H80N2O14: C 61.37, H 9.36, N 3.25; found: C 61.34, H 9.34, N 3.28.

6,11-Di-O-methyl-4″-O-(N-pentylcarbamoyl)erythromycin A (10c)

White solid, yield 74.5%, m.p. 167–170 °C; IR (KBr): 3464, 2966, 2930, 2849, 2367, 1725, 1460, 1170, 1103, 1009 cm−1; 1H NMR (400 MHz, CDCl3): δ 4.98 (d, J=8.3 Hz, 2H), 4.75 (m, 1H), 4.56–4.52 (m, 2H), 4.31 (m, 1H), 3.76 (d, J=6.6 Hz, 1H), 3.72–3.67 (m, 2H), 3.59 (s, 3H), 3.43 (s, 1H), 3.35 (s, 3H), 3.28–3.15 (m, 2H), 3.10 (s, 3H), 3.06–3.04 (m, 2H), 2.97 (m, 1H), 2.63–2.59 (m, 2H), 2.43 (d, J=15.1 Hz, 1H), 2.35 (s, 6H), 2.08–2.05 (m, 2H), 1.95–1.89 (m, 3H), 1.86 (m, 1H), 1.73–1.62 (m, 3H), 1.54–1.44 (m, 5H), 1.39 (s, 3H), 1.36–1.29 (m, 2H), 1.25–1.09 (m, 22H), 0.91–0.88 (m, 3H), 0.85–0.81 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.4, 175.6, 156.3, 101.9, 96.5, 79.5, 78.8, 78.9, 78.6, 77.7, 76.0, 72.9, 71.2, 67.7, 65.1, 63.5, 60.8, 50.6, 49.5, 45.6, 44.8, 41.1, 40.3, 38.0, 37.9, 37.7, 35.4, 31.9, 29.7, 29.6, 28.8, 22.7, 22.3, 21.5, 20.9, 20.3, 19.5, 18.3, 17.4, 16.0, 13.9, 12.8, 10.5, 9.3; MS (ESI) m/z calcd. for C45H82N2O14 874.58; found (M+H+) 875.1; Anal. calcd. (%) for C45H82N2O14: C 61.76, H 9.44, N 3.20; found: C 61.73, H 9.41, N 3.23.

6,11-Di-O-methyl-4″-O-(N-cyclohexylcarbamoyl)erythromycin A (10d)

White solid, yield 70.6%, m.p. 198–203 °C; IR (KBr): 3447, 2974, 2936, 2856, 1724, 1653, 1540, 1457, 1378, 1251, 1172, 1053, 1013 cm−1; 1H NMR (400 MHz, CDCl3): δ 4.97 (d, J=7.7 Hz, 2H), 4.86 (m, 1H), 4.55–4.51 (m, 2H), 4.31 (m, 1H), 3.74 (d, J=6.5 Hz, 1H), 3.71–3.68 (m, 2H), 3.58 (s, 3H), 3.43 (s, 1H), 3.32 (s, 3H), 3.33–3.13 (m, 3H), 3.10 (s, 3H), 3.07–2.98 (m, 2H), 2.96 (m, 1H), 2.62–2.54 (m, 2H), 2.43 (d, J=15.2 Hz, 1H), 2.30 (s, 6H), 2.07–2.03 (m, 2H), 1.92–1.89 (m, 2H), 1.85–1.82 (m, 1H), 1.68–1.63 (m, 4H), 1.55–1.45 (m, 4H), 1.39 (s, 3H), 1.29–0.93 (m, 25H), 0.91–0.87 (m, 3H), 0.84–0.81 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.5, 175.6, 156.3, 102.1, 96.5, 79.5, 78.9, 78.7, 78.6, 77.7, 77.3, 76.0, 73.0, 71.2, 67.8, 65.0, 63.5, 60.8, 50.6, 49.5, 45.6, 44.8, 42.8, 40.2, 38.0, 37.9, 37.7, 35.3, 29.7, 28.9, 23.2, 21.7, 21.5, 20.9, 20.3, 19.4, 18.3, 17.4, 16.0, 12.8, 11.1, 10.5; MS (ESI) m/z calcd. for C46H82N2O14 886.58; found (M+H+) 887.1; Anal. calcd. (%) for C46H82N2O14: C 62.28, H 9.32, N 3.16; found: C 62.25, H 9.30, N 3.19.

611-Di-O-methyl-4″-O-(N-(3-methoxypropyl)carbamoyl)erythromycin A (10e)

White solid, yield 74.6%, m.p. 224–227 °C; IR (KBr): 3445, 2973, 2935, 1725, 1461, 1377, 1345, 1170, 1112, 1059, 1008 cm−1; 1H NMR (400 MHz, CDCl3): δ 5.17 (m, 1H), 4.99–4.97 (m, 2H), 4.58 (d, J=7.2 Hz, 1H), 4.53 (d, J=9.8 Hz, 1H), 4.32 (m, 1H), 3.76 (d, J=6.6 Hz, 1H), 3.73–3.69 (m, 2H), 3.58 (s, 3H), 3.51–3.43 (m, 3H), 3.33 (s, 3H), 3.32 (s, 3H), 3.20 (m, 1H), 3.10 (s, 3H), 3.08–3.02 (m, 2H), 2.98 (m, 1H), 2.63–2.55 (m, 2H), 2.43 (d, J=15.1 Hz, 1H), 2.32 (s, 6H), 2.08–2.03 (m, 2H), 1.95–1.85 (m, 2H), 1.83–1.76 (m, 3H), 1.68–1.63 (m, 4H), 1.52–1.43 (m, 2H), 1.39 (s, 3H), 1.34 (m, 1H), 1.25–1.08 (m, 21H), 0.85–0.81 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.5, 175.6, 156.3, 101.9, 96.4, 79.4, 78.9, 78.8, 78.4, 77.7, 76.0, 72.9, 71.5, 71.2, 67.7, 65.1, 63.4, 60.8, 58.8, 50.6, 49.4, 45.6, 44.7, 40.2, 39.6, 37.9, 37.8, 37.6, 35.4, 29.7, 29.6, 28.9, 21.7, 21.5, 20.9, 20.2, 19.4, 18.4, 17.4, 16.0, 12.8, 10.5, 9.3; MS (ESI) m/z calcd. for C44H80N2O15 876.56; found (M+H+) 877.2; Anal. calcd. (%) for C44H80N2O15: C 60.25, H 9.19, N 3.19; found: C 60.22, H 9.20, N 3.18.

6,11-Di-O-methyl-4″-O-(N-(3-ethoxypropyl)carbamoyl)erythromycin A (10f)

White solid, yield 76.8%, m.p. 198–202 °C; IR (KBr): 3444, 2975, 2935, 2875, 1727, 1504, 1459, 1378, 1266, 1166, 1111, 1051, 1013 cm−1; 1H NMR (400 MHz, CDCl3): δ 5.10 (m, 1H), 4.99–4.96 (m, 2H), 4.57 (d, J=7.3 Hz, 1H), 4.53 (d, J=9.7 Hz, 1H), 4.31 (m, 1H), 3.76 (d, J=6.5 Hz, 1H), 3.75–3.66 (m, 2H), 3.59 (s, 3H), 3.50–3.43 (m, 5H), 3.32 (s, 3H), 3.19 (m, 1H), 3.10 (s, 3H), 2.99–2.97 (m, 2H), 2.93 (m, 1H), 2.63–2.55 (m, 2H), 2.43 (d, J=14.4 Hz, 1H), 2.32 (s, 6H), 2.08–2.05 (m, 3H), 1.99–1.89 (m, 3H), 1.86 (m, 1H), 1.80–1.77 (m, 2H), 1.69–1.63 (m, 3H), 1.49 (m, 1H), 1.39 (s, 3H), 1.34 (m, 1H), 1.27–1.12 (m, 21H), 1.11–1.09 (m, 3H), 0.85–0.81 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.5, 175.6, 156.3, 101.9, 96.4, 79.4, 78.9, 78.5, 77.7, 76.0, 72.9, 71.2, 68.6, 67.7, 66.3, 65.1, 63.5, 60.8, 50.6, 49.4, 45.6, 44.7, 40.2, 39.3, 37.9, 37.8, 37.6, 35.4, 29.8, 29.7, 28.9, 21.7, 21.5, 20.8, 20.3, 19.4, 18.4, 17.4, 16.0, 15.1, 12.8, 10.5, 9.3; MS (ESI) m/z calcd. for C45H82N2O15 890.57; found (M+H+) 891.2; Anal. calcd. (%) for C45H82N2O15: C 60.65, H 9.27, N 3.14; found: C 60.62, H 9.24, N 3.17.

6,11-Di-O-methyl-4″-O-(N-(3-isopropoxypropyl)carbamoyl)erythromycin A (10g)

White solid, yield 70.8%, m.p. 173–176 °C; IR (KBr): 3438, 2972, 2932, 1728, 1716, 1506, 1378, 1265, 1168, 1129, 1051, 1011 cm−1; 1H NMR (400 MHz, CDCl3): δ 5.03 (m, 1H), 4.92–4.90 (m, 2H), 4.50 (d, J=7.2 Hz, 1H), 4.46 (d, J=9.8 Hz, 1H), 4.24 (m, 1H), 3.69 (d, J=6.4 Hz, 1H), 3.62–3.60 (m, 2H), 3.51 (s, 3H), 3.45–3.39 (m, 5H), 3.24 (s, 3H), 3.16–3.12 (m, 2H), 3.03 (s, 3H), 3.00–2.97 (m, 2H), 2.92 (m, 1H), 2.56–2.47 (m, 2H), 2.36 (d, J=15.1 Hz, 1H), 2.26 (s, 6H), 2.01–1.92 (m, 3H), 1.87–1.76 (m, 3H), 1.72–1.68 (m, 2H), 1.61–1.56 (m, 4H), 1.43 (m, 1H), 1.32 (s, 3H), 1.27 (m, 1H), 1.20–1.07 (m, 18H), 1.05–1.02 (m, 6H), 0.85–0.74 (m, 6H); 13C NMR (400 MHz, CDCl3): δ 216.4, 174.5, 155.3, 100.9, 95.4, 78.3, 77.9, 77.8, 77.4, 76.7, 76.3, 75.0, 71.9, 70.6, 70.1, 66.7, 64.1, 62.5, 59.8, 49.6, 48.4, 44.6, 43.7, 39.2, 38.4, 36.9, 36.8, 36.6, 34.4, 29.0, 28.6, 27.9, 21.1, 21.0, 20.7, 20.5, 19.8, 19.2, 18.4, 17.3, 16.4, 15.0, 11.8, 9.5, 8.3; MS (ESI) m/z calcd. for C46H84N2O15 904.59; found (M+H+) 905.2; Anal. calcd. (%) for C46H84N2O15: C 61.04, H 9.35, N 3.09; found: C 61.01, H 9.32, N 3.08.

6,11-Di-O -methyl-4″-O-(N-(3-butoxypropyl)carbamoyl)erythromycin A (10h)

White solid, yield 75.1%, m.p. 148–152 °C; IR (KBr): 3459, 2962, 2929, 2863, 1725, 1461, 1382, 1348, 1268, 1171, 1105 cm−1; 1H NMR (400 MHz, CDCl3): δ 5.03 (m, 1H), 4.92–4.90 (m, 2H), 4.51 (d, J=7.1 Hz, 1H), 4.46 (d, J=9.7 Hz, 1H), 4.15 (m, 1H), 3.69 (d, J=6.2 Hz, 1H), 3.64–3.60 (m, 2H), 3.51 (s, 3H), 3.40–3.32 (m, 5H), 3.24 (s, 3H), 3.18 (m, 1H), 3.03 (s, 3H), 3.01–2.96 (m, 2H), 2.92 (m, 1H), 2.56–2.51 (m, 2H), 2.36 (d, J=15.3 Hz, 1H), 2.27 (s, 6H), 2.01–1.97 (m, 2H), 1.90–1.76 (m, 2H), 1.73–1.69 (m, 2H), 1.67–1.55 (m, 5H), 1.51–1.44 (m, 2H), 1.40–1.34 (m, 4H), 1.32 (s, 3H), 1.28 (m, 1H), 1.20–1.07 (m, 18H), 0.93–0.81 (m, 6H), 0.78–0.74 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.4, 175.5, 156.3, 101.9, 96.4, 79.3, 78.9, 78.8, 78.5, 77.7, 76.0, 72.9, 71.2, 70.9, 68.8, 67.7, 65.1, 63.5, 60.8, 50.6, 49.5, 45.6, 44.7, 40.2, 38.7, 37.9, 37.6, 35.4, 31.7, 30.5, 29.7, 28.9, 23.7, 23.0, 21.7, 20.8, 20.3, 19.2, 18.4, 17.4, 16.0, 13.9, 12.8, 10.5, 9.3; MS (ESI) m/z calcd. for C47H86N2O15 918.60; found (M+H+) 919.2; Anal. calcd. (%) for C47H86N2O15: C 61.41, H 9.43, N 3.05; found: C 61.38, H 9.41, N 3.07.

6,11-Di-O-methyl-4″-O-(N-(3-hydroxypropyl)carbamoyl)erythromycin A (10i)

White solid, yield 66.3%, m.p. 67–72 °C; IR (KBr): 3473, 2962, 2925, 2855, 1722, 1461, 1374, 1257, 1169, 1090, 1052, 938 cm−1; 1H NMR (400 MHz, CDCl3): δ 4.99–4.97 (m, 2H), 4.78 (m, 1H), 4.64 (d, J=11.2 Hz, 1H), 4.03 (m, 1H), 3.73 (d, J=6.0 Hz, 1H), 3.65–3.57 (m, 2H), 3.59 (s, 3H), 3.58–3.48 (m, 3H), 3.43 (s, 1H), 3.39 (s, 3H), 3.10 (m, 1H), 3.09 (s, 3H), 3.07–3.03 (m, 2H), 2.99 (m, 1H), 2.69–2.58 (m, 2H), 2.38 (d, J=15.0 Hz, 1H), 2.27 (s, 6H), 2.23 (m, 1H), 2.10–1.99 (m, 4H), 1.97–1.92 (m, 2H), 1.76–1.72 (m, 3H), 1.69–1.62 (m, 2H), 1.55–1.42 (m, 2H), 1.39 (s, 3H), 1.32–1.24 (m, 11H), 1.16–1.11 (m, 6H), 0.89–0.82 (m, 6H); 13C NMR (400 MHz, CDCl3): δ 217.4, 175.4, 170.0, 100.2, 96.1, 81.2, 79.5, 78.9, 78.3, 77.8, 77.5, 76.0, 72.8, 71.8, 68.1, 66.0, 63.5, 60.8, 50.4, 49.3, 45.8, 45.6, 44.9, 40.7, 37.9, 37.8, 37.2, 35.0, 31.9, 29.7, 29.4, 22.7, 21.6, 21.5, 21.3, 20.4, 18.7, 17.6, 16.1, 12.8, 10.4, 9.1; MS (ESI) m/z calcd. for C43H78N2O15 862.54; found (M+H+) 862.9; Anal. calcd. (%) for C43H78N2O15: C 59.84, H 9.11, N 3.25; found: C 59.82, H 9.09, N 3.27.

611-Di-O-methyl-4″-O-(N-furfurylcarbamoyl)erythromycin A (10j)

White solid, yield 63.7%, m.p. 240–243 °C; IR (KBr): 3481, 3333, 2976, 2942, 2360, 1733, 1684, 1507, 1457, 1381, 1246, 1126, 1107, 1052, 1010 cm−1; 1H NMR (400 MHz, CDCl3): δ 7.37 (d, J=3.1 Hz, 2H), 6.34 (m, 1H), 6.25 (d, J=3.2 Hz, 1H), 5.13 (m, 1H), 5.01–4.98 (m, 2H), 4.58–4.56 (m, 2H), 4.41–4.40 (m, 2H), 4.34 (m, 1H), 3.76 (d, J=6.8 Hz, 1H), 3.73–3.71 (m, 2H), 3.51 (s, 3H), 3.45 (m, 1H), 3.36 (s, 3H), 3.21 (m, 1H), 3.12 (s, 3H), 3.08–3.06 (m, 2H), 3.01 (m, 1H), 2.62–2.55 (m, 2H), 2.45 (d, J=14.8 Hz, 2H), 2.32 (s, 6H), 2.24 (m, 1H), 2.07 (m, 1H), 1.91 (m, 1H), 1.84 (m, 1H), 1.82–1.58 (m, 6H), 1.37 (s, 3H), 1.33 (m, 1H), 1.32–1.26 (m, 18H), 0.87–0.83 (m, H); 13C NMR (400 MHz, CDCl3): δ 217.5, 175.5, 156.1, 142.2, 110.4, 107.1, 102.0, 96.4, 79.4, 79.2, 78.9, 78.6, 77.7, 76.0, 72.9, 71.2, 67.8, 65.0, 63.4, 60.8, 50.5, 49.5, 45.6, 44.7, 40.2, 38.0, 37.9, 37.6, 35.3, 29.7, 28.8, 21.6, 21.5, 20.8, 20.2, 19.4, 18.3, 17.4, 16.0, 12.8, 10.5, 9.3; MS (ESI) m/z calcd. for C45H80N2O15 888.56; found (M+H+) 889.1; Anal. calcd. (%) for C47H86N2O15:C 60.79, H 9.07, N 3.15; found: C 60.78, H 9.04, N 3.13.

6,11-Di-O-methyl-4″-O-(N-benzylcarbamoyl)erythromycin A (10k)

White solid, yield 73.6%, m.p. 234–238 °C; IR (KBr): 3357, 2976, 2939, 1723, 1460, 1383, 1346, 1257, 1168, 1103, 1071, 1011 cm−1; 1H NMR (400 MHz, CDCl3): δ 7.34–7.32 (m, 2H), 7.30–7.27 (m, 3H), 5.22 (m, 1H), 4.99–4.97 (m, 2H), 4.59–4.53 (m, 2H), 4.42–4.41 (m, 2H), 4.33 (m, 1H), 3.75 (d, J=6.4 Hz, 1H), 3.71 (d, J=10.0 Hz, 1H), 3.65 (m, 1H), 3.59 (s, 3H), 3.46–3.34 (m, 2H), 3.32 (s, 3H), 3.19 (m, 1H), 3.11 (s, 3H), 3.08–3.00 (m, 3H), 2.61 (m, 1H), 2.52 (m, 1H), 2.44 (d, J=15.1 Hz, 1H), 2.27 (s, 6H), 2.16–1.95 (m, 3H), 1.93–1.86 (m, 3H), 1.70–1.59 (m, 3H), 1.49 (m, 1H), 1.40 (s, 3H), 1.30 (m, 1H), 1.26–1.09 (m, 21H), 0.85–0.81 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.2, 175.6, 156.4, 138.4, 128.7, 127.6, 127.3, 102.1, 96.4, 79.5, 79.1, 78.9, 78.6, 77.7, 76.1, 72.9, 71.2, 67.8, 65.0, 63.4, 60.8, 50.6, 49.5, 45.6, 45.2, 44.8, 40.2, 38.0, 37.9, 37.7, 35.4, 29.7, 28.8, 21.7, 21.5, 20.9, 20.3, 19.4, 18.4, 17.4, 16.0, 12.8, 10.5, 9.3; MS (ESI) m/z calcd. for C47H78N2O14 894.55; found (M+H+) 895.1; Anal. calcd. (%) for C47H78N2O14: C 63.06, H 8.78, N 3.13; found: C 63.03, H 8.76, N 3.16.

6,11-Di-O-methyl-4″-O -(N-(4-methoxybenzyl)carbamoyl)erythromycin A (10l)

White solid, yield 69.2%, m.p. 193–196 °C; IR (KBr): 3402, 2972, 2935, 2360, 1722, 1620, 1461, 1379, 1242, 1172, 1103, 1078, 1021 cm−1; 1H NMR (400 MHz, CDCl3): δ 7.18 (d, J=8.3 Hz, 2H), 6.85 (d, J=8.4 Hz, 2H), 5.11 (m, 1H), 4.96 (m, 2H), 4.57–4.52 (m, 2H), 4.33–4.32 (m, 3H), 3.78 (s, 3H), 3.74 (d, J=6.5 Hz, 1H), 3.69 (d, J=6.1 Hz, 1H), 3.57 (m, 1H), 3.42 (s, 3H), 3.39–3.34 (m, 2H), 3.29 (s, 3H), 3.22 (m, 1H), 3.09 (s, 3H), 3.07–2.99 (m, 3H), 2.71–2.60 (m, 2H), 2.42 (d, J=15.2 Hz, 1H), 2.26 (s, 6H), 2.16–1.95 (m, 3H), 1.90–1.84 (m, 2H), 1.68–1.62 (m, 4H), 1.58–1.42 (m, 2H), 1.38 (s, 3H), 1.31 (m, 1H), 1.27–0.94 (m, 18H), 0.90–0.86 (m, 3H), 0.84–0.80 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.5, 175.5, 159.0, 156.3, 130.5, 128.6, 114.0, 102.0, 96.4, 79.3, 79.0, 78.9, 78.5, 77.7, 77.5, 76.0, 72.8, 71.1, 67.7, 64.9, 63.4, 60.7, 59.0, 55.2, 50.6, 49.4, 45.8, 44.7, 44.6, 40.2, 37.9, 37.8, 37.6, 35.3, 29.6, 28.7, 21.6, 21.5, 20.8, 20.2, 19.4, 18.4, 17.4, 16.0, 12.8, 10.4, 9.2; MS (ESI) m/z calcd. for C48H80N2O15 924.56; found (M+H+) 925.1; Anal. calcd. (%) for C48H80N2O15: C 62.32, H 8.72, N 2.88; found: C 62.30, H 8.69, N 2.90.

611-Di-O-methyl-4″-O-(N-(4-fluorobenzyl)carbamoyl)erythromycin A (10m)

White solid, yield 68.5%, m.p. 129–133 °C; IR (KBr): 3399, 2968, 2937, 1723, 1616, 1517, 1462, 1379, 1344, 1256, 1172, 1102, 1023 cm−1; 1H NMR (400 MHz, CDCl3): δ 7.22–7.19 (m, 2H), 6.88–6.86 (m, 2H), 5.11 (m, 1H), 5.00 (m, 2H), 4.59–4.54 (m, 2H), 4.35–4.34 (m, 3H), 3.75 (d, J=6.3 Hz, 1H), 3.71 (d, J=10.0 Hz, 1H), 3.66 (m, 1H), 3.59 (s, 3H), 3.44 (s, 1H), 3.31 (s, 3H), 3.20 (m, 2H), 3.11 (s, 3H), 3.08–3.03 (m, 2H), 3.01 (m, 1H), 2.61–2.53 (m, 2H), 2.44 (d, J=15.4 Hz, 1H), 2.30 (s, 6H), 2.17 (s, 1H), 2.08–2.05 (m, 2H), 1.95–1.89 (m, 2H), 1.83 (m, 1H), 1.70–1.63 (m, 3H), 1.50 (m, 1H), 1.40 (s, 3H), 1.32 (m, 1H), 1.26–1.09 (m, 21H), 0.86–0.82 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.5, 175.5, 159.0, 156.3, 130.5, 128.7, 114.0, 101.9, 96.4, 79.4, 79.0, 78.9, 78.5, 76.0, 72.9, 71.1, 67.7, 65.0, 63.4, 60.8, 55.2, 50.6, 49.4, 45.5, 44.7, 44.6, 40.2, 37.9, 37.8, 37.6, 35.3, 29.6, 28.9, 21.6, 21.5, 20.8, 20.2, 19.4, 18.4, 17.4, 16.0, 12.8, 10.4, 9.3; MS (ESI) m/z calcd. for C47H77FN2O14 912.54; found (M+H+) 913.1; Anal. calcd. (%) for C47H77FN2O14: C 61.82, H 8.50, F 2.08, N 3.07; found: C 61.78, H 8.48, F 2.07, N 3.09.

611-Di-O-methyl-4″-O-(N-(4-chlorobenzyl)carbamoyl)erythromycin A (10n)

White solid, yield 73.3%, m.p. 123–127 °C; IR (KBr): 3454, 2958, 2925, 2856, 1723, 1638, 1460, 1342, 1260, 1174, 1103, 1016 cm−1; 1H NMR (400 MHz, CDCl3): δ 7.25 (d, J=8.7 Hz, 2H), 6.92 (d, J=9.1 Hz, 2H), 5.28 (m, 1H), 4.91–4.87 (m, 2H), 4.44 (d, J=7.2 Hz, 1H), 4.19–4.15 (m, 2H), 3.98 (m, 1H), 3.70 (d, J=6.7 Hz, 1H), 3.64–3.60 (m, 2H), 3.52 (s, 3H), 3.49–3.42 (m, 2H), 3.37 (s, 1H), 3.27 (s, 3H), 3.17 (m, 1H), 3.03 (s, 3H), 2.99–2.96 (m, 2H), 2.93 (m, 1H), 2.55–2.53 (m, 3H), 2.32 (s, 6H), 2.28–2.11 (m, 2H), 2.00–1.90 (m, 3H), 1.88–1.67 (m, 2H), 1.61–1.50 (m, 2H), 1.38 (m, 1H), 1.34 (s, 3H), 1.31 (m, 1H), 1.29–1.10 (m, 12H), 1.09–0.95 (m, 6H), 0.85–0.75 (m, 6H); 13C NMR (400 MHz, CDCl3): δ 217.4, 175.6, 157.0, 139.9, 131.9, 130.0, 128.8, 102.4, 96.4, 79.9, 78.9, 78.7, 77.8, 77.5, 76.0, 72.1, 71.0, 68.4, 66.0, 65.6, 60.8, 50.5, 49.4, 45.4, 44.9, 41.2, 40.3, 38.2, 38.0, 37.7, 35.3, 29.7, 29.4, 22.7, 21.4, 20.4, 19.4, 18.7, 17.4, 16.0, 14.1, 12.8, 10.5, 9.3; MS (ESI) m/z calcd. for C47H77ClN2O14 928.51; found (M+H+) 929.2; Anal. calcd. (%) for C47H77ClN2O14: C 60.73, H 8.35, Cl 3.81, N 3.01; found: C 60.70, H 8.32, Cl 3.79, N 3.03.

6,11-Di-O-methyl-4″-O-(N-(4-bromobenzyl)carbamoyl)erythromycin (10o)

White solid, yield 74.6%, m.p. 113–117 °C; IR (KBr): 3446, 3280, 2956, 2924, 2852, 1729, 1646, 1557, 1458, 1382, 1260, 1176, 1091, 1013 cm−1; 1H NMR (400 MHz, CDCl3): δ 7.46 (d, J=8.4 Hz, 2H), 7.16(d, J=8.3 Hz, 2H), 4.98 (m, 1H), 4.95–4.94 (m, 2H), 4.50 (d, J=7.2 Hz, 1H), 4.39–4.38 (m, 2H), 4.05 (m, 1H), 3.77 (d, J=6.7 Hz, 1H), 3.71 (m, 1H), 3.59 (s, 3H), 3.55 (m, 2H), 3.49 (s, 1H), 3.44 (s, 1H), 3.34 (s, 3H), 3.26 (m, 1H), 3.10 (s, 3H), 3.07–3.02 (m, 2H), 3.00 (m, 1H), 2.62 (m, 1H), 2.53 (m, 1H), 2.39 (m, 1H), 2.36 (s, 6H), 2.23 (m, 1H), 1.97–1.84 (m, 2H), 1.82–1.72 (m, 3H), 1.66–1.62 (m, 2H), 1.60–1.59 (m, 1H), 1.46 (m, 1H), 1.41 (s, 3H), 1.38 (m, 1H), 1.31–1.21 (m, 12H), 1.15–1.09 (m, 9H), 0.85–0.81 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.5, 175.6, 155.1, 137.4, 131.7, 129.5, 121.3, 102.4, 96.3, 79.8, 79.0, 77.4, 77.1, 76.0, 72.8, 71.0, 68.2, 66.0, 65.6, 60.8, 50.6, 49.5, 45.5, 44.9, 43.0, 40.3, 38.2, 38.0, 37.6, 35.0, 29.7, 23.2, 22.7, 21.7, 21.5, 20.4, 19.4, 18.7, 16.1, 14.1, 12.8, 10.5, 9.3; MS (ESI) m/z calcd. for C47H77BrN2O14 972.46; found (M+H+) 973.1; Anal. calcd. (%) for C47H77BrN2O14: C 57.96, H 7.97, Br 8.20, N 2.88; found: C 57.93, H 7.94, Br 8.18, N 2.89.

6,11-Di-O-methyl-4″-O-(N-(4-hydroxybenzyl)carbamoyl)erythromycin A (10p)

White solid, yield 65.8%, m.p. 135–139 °C; IR (KBr): 3446, 2975, 2935, 2359, 1732, 1558, 1457, 1383, 1260, 1171, 1108, 1073, 1012 cm−1; 1H NMR (400 MHz, CDCl3): δ 7.06 (d, J=8.3 Hz, 2H), 6.78 (d, J=8.2 Hz, 2H), 5.30 (m, 1H), 5.21 (m, 1H), 4.99–4.97 (m, 2H), 4.63–4.50 (m, 2H), 4.35–4.21 (m, 3H), 3.74 (d, J=6.6 Hz, 1H), 3.70 (d, J=9.9 Hz, 1H), 3.66 (m, 1H), 3.59 (s, 3H), 3.44 (m, 1H), 3.11 (s, 3H), 3.25–3.16 (m, 2H), 3.10 (s, 3H), 3.06–3.00 (m, 3H), 2.72–2.53 (m, 2H), 2.43 (d, J=14.8 Hz, 1H), 2.31 (s, 6H), 2.18–1.97 (m, 3H), 1.91–1.82 (m, 2H), 1.67–1.59 (m, 4H), 1.49 (m, 1H), 1.39 (s, 3H), 1.34–1.30 (m, 2H), 1.29–1.04 (m, 18H), 0.91–0.82 (m, 6H); 13C NMR (400 MHz, CDCl3): δ 217.8, 175.6, 156.7, 156.3, 129.0, 128.8, 115.7, 102.0, 96.4, 79.5, 78.9, 78.6, 77.7, 76.1, 73.0, 71.2, 67.7, 64.8, 63.5, 60.8, 53.5, 50.6, 49.5, 44.8, 44.7, 40.2, 38.0, 37.9, 37.7, 35.3, 29.7, 28.5, 21.6, 21.5, 20.9, 20.3, 19.4, 18.4, 17.4, 16.1, 12.8, 10.5, 9.4; MS (ESI) m/z calcd. for C47H78N2O15 910.54; found (M+H+) 910.0; Anal. calcd. (%) for C47H78N2O15: C 61.96, H 8.63, N 3.07; found: C 61.94, H 8.60, N 3.09.

6,11-Di-O-methyl-4″-O -(N-(phenylethyl)carbamoyl)erythromycin A (10q)

White solid, yield 78.6%, m.p. 204–207 °C; IR (KBr): 3528, 3460, 3282, 2975, 2936, 1719, 1459, 1398, 1344, 1255, 1173, 1056, 1009 cm−1; 1H NMR (400 MHz, CDCl3): δ 7.33–7.30 (m, 2H), 7.26–7.19 (m, 3H), 4.99–4.98 (m, 2H), 4.80 (m, 1H), 4.53 (d, J=8.8 Hz, 1H), 3.74 (d, J=6.3 Hz, 1H), 3.71 (d, J=10.4 Hz, 1H), 3.59 (s, 3H), 3.56–3.54 (m, 2H), 3.49–3.44 (m, 2H), 3.30 (s, 3H), 3.19 (m, 1H), 3.11 (s, 3H), 3.06 (m, 1H), 2.99 (m, 1H), 2.89–2.85 (m, 2H), 2.60 (m, 1H), 2.54 (m, 1H), 2.43 (d, J=15.2 Hz, 1H), 2.31 (s, 6H), 2.17 (m, 1H), 2.07 (m, 1H), 1.94 (m, 1H), 1.85 (m, 1H), 1.67–1.63 (m, 2H), 1.58 (m, 1H), 1.48 (m, 1H), 1.39 (s, 3H), 1.34 (m, 1H), 1.26 (s, 3H), 1.23–1.04 (m, 21H), 0.86–0.82 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.5, 175.6, 156.2, 138.6, 128.8, 128.6, 126.6, 102.0, 96.4, 79.4, 78.9, 77.7, 77.4, 77.3, 77.1, 76.7, 76.0, 72.9, 71.2, 67.7, 65.0, 63.4, 60.8, 50.6, 49.5, 45.6, 44.8, 42.1, 40.2, 38.0, 37.9, 37.7, 35.9, 35.4, 29.7, 28.8, 21.6, 21.5, 20.9, 20.3, 19.5, 18.3, 17.4, 16.1, 12.8, 10.5, 9.3; MS (ESI) m/z calcd. for C48H80N2O14 908.56; found (M+H+) 909.2; Anal. calcd. (%) for C47H78N2O15: C 63.41, H 8.87, N 3.08; found: C 63.38, H 8.85, N 3.06.

6,11-Di-O-methyl-4″-O-(N-(4-methoxyphenylethyl)carbamoyl)erythromycin A (10r)

White solid, yield 64.8%, m.p.146–149 °C; IR (KBr): 3453, 2960, 2925, 2857, 1730, 1460, 1377, 1262, 1171, 1080, 1040 cm−1; 1H NMR (400 MHz, CDCl3): δ 7.67–7.63 (m, 2H), 7.47–7.45 (m, 2H), 4.91–4.87 (m, 2H), 4.42 (d, J=7.2 Hz, 1H), 4.19–4.10 (m, 2H), 3.96 (m, 1H), 3.74 (m, 1H), 3.69 (d, J=6.7 Hz, 1H), 3.63 (d, J=9.7 Hz, 1H), 3.52 (s, 3H), 3.47–3.37 (m, 3H), 3.26 (s, 3H), 3.14 (m, 1H), 3.03 (s, 3H), 2.99–2.89 (m, 2H), 2.86 (m, 1H), 2.71 (m, 1H), 2.54 (m, 1H), 2.40 (m, 1H), 2.30 (d, J=15.3 Hz, 1H), 2.25 (s, 6H), 2.13 (m, 1H), 1.98 (m, 1H), 1.87–1.76 (m, 2H), 1.68–1.51 (m, 3H), 1.44–1.38 (m, 2H), 1.34 (s, 3H), 1.30 (m, 1H), 1.32–1.02 (m, 12H), 0.98–0.80 (m, 6H), 0.78–0.74 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 216.3, 174.5, 166.7, 160.1, 131.4, 129.9, 127.8, 101.4, 95.3, 80.5, 78.9, 78.0, 76.9, 75.0, 71.7, 70.0, 67.5, 67.1, 64.9, 64.5, 59.8, 54.3, 49.5, 48.5, 44.5, 43.9, 41.8, 39.2, 38.3, 37.7, 37.2, 36.9, 36.7, 29.3, 27.9, 22.7, 22.0, 21.7, 20.4, 19.3, 18.4, 18.2, 17.7, 13.0, 9.9, 9.5; MS (ESI) m/z calcd. for C49H82N2O15 938.57; found (M+H+) 939.2; Anal. calcd. (%) for C49H82N2O15: C 62.66, H 8.80, N 2.98; found: C 62.63, H 8.78, N 2.96.

6,11-Di-O-methyl-4″-O-(N-(3,4-dimethoxyphenylethyl)carbamoyl)erythromycin A (10s)

White solid, yield 74.9%, m.p. 217–220 °C; IR (KBr): 3446, 2974, 2937, 1730, 1652, 1558, 1516, 1457, 1378, 1237, 1171, 1109, 1074, 1012 cm−1; 1H NMR (400 MHz, CDCl3): δ 6.78 (m, 1H), 6.72 (m, 2H), 4.97 (d, J=7.2 Hz, 2H), 4.85 (m, 1H), 4.52 (d, J=9.0 Hz, 2H), 4.28 (m, 1H), 3.87 (s, 3H), 3.86 (s, 3H), 3.73 (d, J=6.4 Hz, 1H), 3.69 (d, J=10.2 Hz, 1H), 3.58 (s, 3H), 3.53–3.36 (m, 3H), 3.32 (m, 1H), 3.30 (s, 3H), 3.19 (m, 1H), 3.10 (s, 3H), 3.07–3.04 (m, 2H), 2.99 (m, 1H), 2.79 (m, 2H), 2.64–2.54 (m, 2H), 2.42 (d, J=15.1 Hz, 1H), 2.31 (s, 6H), 2.16 (m, 1H), 2.06 (m, 1H), 1.97–1.82 (m, 2H), 1.65–1.57 (m, 3H), 1.49–1.43 (m, 2H), 1.38 (s, 3H), 1.32 (m, 1H), 1.31–1.04 (m, 21H), 0.85–0.81 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.5, 175.5, 156.2, 149.0, 147.7, 130.9, 120.7, 111.8, 111.2, 101.9, 96.4, 79.4, 78.9, 78.5, 77.7, 76.0, 72.9, 71.1, 67.7, 64.9, 63.4, 60.8, 58.8, 55.9, 55.8, 50.6, 49.4, 45.5, 44.7, 42.2, 40.2, 37.9, 37.8, 37.6, 35.5, 35.3, 29.7, 28.8, 21.6, 21.5, 20.8, 20.3, 19.4, 18.3, 17.4, 16.0, 12.8, 10.5, 9.3, 8.3; MS (ESI) m/z calcd. for C50H84N2O16 968.58; found (M+H+) 969.3; Anal. calcd. (%) for C50H84N2O16: C 61.96, H 8.74, N 2.89; found: C 61.94, H 8.71, N 2.86.

6,11-Di-O-methyl-4″-O-(N-(4-hydroxyphenylethyl)carbamoyl)erythromycin A (10t)

White solid, yield 74.3%, m.p. 78–81 °C; IR (KBr): 3371, 2976, 2937, 1721, 1657, 1554, 1461, 1379, 1257, 1171, 1078, 939 cm−1; 1H NMR (400 MHz, CDCl3): δ 6.87 (d, J=7.9 Hz, 2H), 6.73 (d, J=8.3 Hz, 2H), 5.30–5.21 (m, 3H), 4.87–4.85 (m, 2H), 4.46 (m, 1H), 3.58 (d, J=7.1 Hz,1H), 3.56–3.54 (m, 2H), 3.46 (s, 3H), 3.45–3.41 (m, 3H), 3.26 (s, 3H), 3.23 (m, 1H), 3.13 (s, 3H), 3.10–3.08 (m, 2H), 2.98 (m, 1H), 2.95–2.88 (m, 2H), 2.61–2.49 (m, 5H), 2.32 (s,6H), 2.16 (m, 1H), 2.02–1.97 (m, 2H), 1.80 (m, 1H), 1.69–1.62 (m, 3H), 1.55–1.52 (m, 2H), 1.31 (s, 3H), 1.26 (m, 1H), 1.22–0.98 (m, 21H), 0.73–0.70 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.7, 175.4, 156.2, 156.0, 132.2, 130.9, 129.6, 115.7, 115.6, 101.6, 96.3, 79.4, 78.8, 78.5, 78.3, 77.7, 76.0, 72.9, 71.0, 67.2, 64.9, 63.4, 60.2, 50.5, 49.4, 44.7, 42.3, 40.1, 39.6, 38.1, 37.5, 34.8, 34.4, 30.5, 29.6, 23.1, 21.5, 21.3, 20.8, 20.3, 19.3, 18.3, 17.4, 16.0, 12.8, 10.4, 9.4; MS (ESI) m/z calcd. for C48H80N2O15 924.56; found (M+H+) 925.2; Anal. calcd. (%) for C48H80N2O15: C 62.32, H 8.72, N 3.03; found: C 62.29, H 8.70, N 3.05.

6,11-Di-O-methyl-4″-O-(N-(4-fluorophenylethyl)carbamoyl)erythromycin A (10u)

White solid, yield 69.5%, m.p. 71–75 °C; IR (KBr): 3435, 2962, 2929, 1722, 1658, 1514, 1460, 1249, 1169, 1111, 1054 cm−1; 1H NMR (400 MHz, CDCl3): δ 7.15–7.13 (m, 2H), 7.00–6.96 (m, 2H), 4.96–4.93 (m, 3H), 4.54 (d, J=7.2 Hz, 1H), 4.51 (d, J=9.8 Hz, 1H), 4.26 (m, 1H), 3.73 (d, J=6.5 Hz, 1H), 3.70 (d, J=10.0 Hz, 1H), 3.60 (m, 1H), 3.58 (s, 3H), 3.51–3.39 (m, 3H), 3.30 (s, 3H), 3.22 (m, 1H), 3.10 (s, 3H), 3.07–3.02 (m, 2H), 2.98 (m, 1H), 2.83–2.80 (m, 2H), 2.71–2.53 (m, 5H), 2.40 (s, 6H), 2.20 (m, 1H), 2.08–2.00 (m, 2H), 1.91 (m, 1H), 1.69–1.60 (m, 3H), 1.57–1.43 (m, 2H), 1.42 (s, 3H), 1.34 (m, 1H), 1.25–1.05 (m, 18H), 0.93–0.88 (m, 3H), 0.84–0.81 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.3, 175.8, 163.0, 156.4, 134.3, 130.2, 130.1, 115.4, 115.2, 101.8, 96.4, 79.5, 78.9, 78.7, 78.5, 77.7, 76.0, 72.9, 71.1, 67.5, 64.8, 63.4, 60.8, 50.5, 49.4, 45.4, 44.7, 42.1, 40.1, 38.0, 37.6, 35.3, 35.1, 34.4, 31.9, 29.6, 22.6, 21.4, 20.8, 20.3, 19.4, 18.3, 17.4, 16.0, 12.8, 10.4, 9.3; MS (ESI) m/z calcd. for C48H79FN2O14 926.55; found (M+H+) 927.2; Anal. calcd. (%) for C48H79FN2O14: C 62.18, H 8.59, F 2.05, N 3.02; found: C 62.16, H 8.57, F 2.02, N 3.04.

6,11-Di-O-methyl-4″-O-(N-(2-fluorophenylethyl)carbamoyl)erythromycin A (10v)

White solid, yield 77.0%, m.p. 134–138 °C; IR (KBr): 3534, 2964, 2934, 2360, 1722, 1652, 1495, 1383, 1231, 1172, 1107, 1053, 1013 cm−1; 1H NMR (400 MHz, CDCl3): δ 7.17–7.10 (m, 2H), 7.02–6.93 (m, 2H), 4.91–4.89 (m, 2H), 4.74 (m, 1H), 4.47–4.42 (m, 2H), 4.14 (m, 1H), 3.67 (d, J=6.7 Hz, 1H), 3.63 (d, J=9.95 Hz, 1H), 3.51 (s, 3H), 3.48–3.36 (m, 3H), 3.22 (s, 3H), 3.14 (m, 1H), 3.03 (s, 3H), 3.01–2.97 (m, 2H), 2.92 (m, 1H), 2.83–2.80 (m, 2H), 2.53 (m, 1H), 2.45 (m, 1H), 2.35 (d, J=15.1 Hz, 1H), 2.23 (s, 6H), 2.13 (m, 1H), 1.98 (m, 1H), 1.90–1.76 (m, 2H), 1.67–1.53 (m, 3H), 1.44–1.34 (m, 2H), 1.32 (s, 3H), 1.25 (m, 1H), 1.18–0.87 (m, 18H), 0.84–0.74 (m, 6H); 13C NMR (400 MHz, CDCl3): δ 217.5, 175.6, 168.0, 156.2, 132.6, 130.9, 128.8, 124.2, 115.4, 101.9, 96.3, 79.4, 78.9, 78.6, 77.7, 76.0, 72.9, 71.2, 67.8, 65.6, 65.0, 63.4, 60.8, 50.6, 49.5, 45.7, 44.8, 41.1, 40.2, 37.9, 37.7, 35.4, 30.7, 29.7, 28.9, 21.7, 20.8, 20.3, 19.3, 18.3, 17.4, 16.1, 12.8, 10.5, 9.3; MS (ESI) m/z calcd. for C48H79FN2O14 926.55; found (M+H+) 927.2; Anal. calcd. (%) for C48H79FN2O14: C 62.18, H 8.59, F 2.05, N 3.02; found: C 62.15, H 8.57, F 2.02, N 3.05.

6,11-Di-O-methyl-4″-O-(N-(2-chlorophenylethyl)carbamoyl)erythromycin A (10w)

White solid, yield 75.4%, m.p. 180–184 °C; IR (KBr): 3371, 2976, 2937, 1721, 1657, 1554, 1461, 1379, 1257, 1171, 1078, 999 cm−1; 1H NMR (400 MHz, CDCl3): δ 7.36 (m, 1H), 7.29–7.19 (m, 3H), 4.98–4.96 (m, 2H), 4.83 (m, 1H), 4.53–4.52 (m, 2H), 4.29 (m, 1H), 3.74 (d, J=6.2 Hz, 1H), 3.69 (d, J=9.5 Hz, 1H), 3.58 (s, 3H), 3.53–3.43 (m, 3H), 3.29 (s, 3H), 3.20 (m, 1H), 3.10 (s, 3H), 3.07–2.99 (m, 5H), 2.79 (m, 2H), 2.60–2.51 (m, 2H), 2.42 (d, J=15.1 Hz, 1H), 2.29 (s, 6H), 2.17 (m, 1H), 2.05 (m, 1H), 2.04–1.86 (m, 2H), 1.67–1.60 (m, 3H), 1.49–1.47 (m, 2H), 1.39 (s, 3H), 1.34 (m, 1H), 1.32–1.09 (m, 21H), 0.85–0.82 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.5, 175.6, 156.2, 136.2, 134.2, 131.0, 129.6, 128.1, 126.9, 102.0, 96.4, 79.4, 78.9, 78.6, 77.7, 76.0, 72.9, 71.2, 67.8, 65.0, 63.4, 60.8, 50.6, 49.5, 45.6, 44.7, 40.6, 40.2, 38.0, 37.9, 37.7, 35.4, 33.7, 29.7, 28.7, 21.7, 21.5, 20.9, 20.3, 19.5, 18.3, 17.4, 16.1, 12.8, 10.5, 9.3; MS (ESI) m/z calcd. for C48H79ClN2O14 942.52; found (M+H+) 943.1; Anal. calcd. (%) for C48H79ClN2O14: C 61.10, H 8.44, Cl 3.76, N 2.97; found: C 61.07, H 8.41, Cl 3.73, N 3.00.

6,11-Di-O-methyl-4″-O-(N-(2-bromophenylethyl)carbamoyl)erythromycin A (10x)

White solid, yield 71.5%, m.p. 157–160 °C; IR (KBr): 3461, 2970, 2928, 2360, 2341, 1712, 1461, 1378, 1344, 1246, 1172, 1108, 1013 cm−1; 1H NMR (400 MHz, CDCl3): δ 7.56 (m, 1H), 7.26–7.23 (m, 2H), 7.12 (m, 1H), 5.01–4.99 (m, 2H), 4.85 (m, 1H), 4.57–4.53 (m, 2H), 4.32 (m, 1H), 3.76 (d, J=7.0 Hz, 1H), 3.72 (d, J=9.7 Hz, 1H), 3.61 (s, 3H), 3.57–3.48 (m, 2H), 3.45 (s, 1H), 3.31 (s, 3H), 3.22 (m, 1H), 3.12 (s, 3H), 3.10–3.05 (m, 2H), 3.04–2.98 (m, 3H), 2.65–2.60 (m, 2H), 2.44 (d, J=15.2 Hz, 1H), 2.33 (s, 6H), 2.21 (m, 1H), 2.09–2.03 (m, 2H), 1.90 (m, 1H), 1.87 (m, 1H), 1.83–1.64 (m, 3H), 1.57–1.45 (m, 2H), 1.41 (s, 3H), 1.35–1.11 (m, 18H), 0.90–0.83 (m, 6H); 13C NMR (400 MHz, CDCl3): δ 217.5, 175.6, 156.3, 138.0, 133.0, 131.0, 128.4, 127.6, 124.6, 102.0, 96.5, 81.2, 79.5, 78.6, 77.7, 76.1, 73.0, 71.2, 67.8, 65.0, 63.4, 60.8, 50.7, 49.5, 45.6, 44.8, 40.7, 40.3, 38.0, 37.9, 37.7, 36.1, 35.4, 29.7, 28.9, 21.7, 21.5, 20.9, 20.3, 19.5, 18.4, 17.4, 16.1, 12.8, 10.5, 9.3; MS (ESI) m/z calcd. for C48H79BrN2O14 986.47; found (M+H+) 987.1; Anal. calcd. (%) for C48H79BrN2O14: C 58.35, H 8.06, Br 8.09, N 2.84; found: C 58.32, H 8.04, Br 8.07, N 2.86.

6,11-Di-O-methyl-4″-O-(N-(3,4-methylenedioxyphenethyl)carbamoyl)erythromycin A (10y)

White solid, yield 62.8%, m.p. 123–126 °C; IR (KBr): 3514, 2974, 2933, 1722, 1504, 1461, 1378, 1249, 1171, 1109, 1071, 1036, 1012 cm−1; 1H NMR (400 MHz, CDCl3): δ 6.64 (d, J=8.3 Hz, 1H), 6.60 (s, 1H), 6.56 (d, J=7.8 Hz, 1H), 5.86 (m, 2H), 4.96–4.89 (m, 2H), 4.78 (m, 1H), 4.47–4.43 (m, 2H), 4.20 (m, 1H), 3.67 (d, J=6.6 Hz, 1H), 3.63 (d, J=9.9 Hz, 1H), 3.51 (s, 3H), 3.43–3.25 (m, 3H), 3.23 (s, 3H), 3.13 (m, 1H), 3.03 (s, 3H), 3.00–2.97 (m, 2H), 2.92 (m, 1H), 2.70–2.66 (m, 2H), 2.56–2.46 (m, 2H), 2.35 (d, J=15.1 Hz, 1H), 2.25 (s, 6H), 2.09 (m, 1H), 2.01–1.90 (m, 2H), 1.87–1.75 (m, 2H), 1.61–1.53 (m, 3H), 1.42 (m, 1H), 1.31 (s, 3H), 1.25 (m, 1H), 1.10–0.99 (m, 21H), 0.77–0.74 (m, 3H); 13C NMR (400 MHz, CDCl3): δ 217.6, 175.8, 156.2, 147.9, 146.1, 132.3, 121.6, 109.0, 108.3, 101.9, 100.9, 96.4, 79.4, 78.9, 78.8, 78.6, 76.0, 72.9, 71.1, 67.7, 64.9, 63.4, 60.8, 50.6, 49.4, 45.6, 44.7, 42.3, 40.2, 37.9, 37.6, 35.6, 35.3, 29.6, 29.4, 29.1, 21.5, 20.8, 20.3, 19.4, 18.3, 17.4, 16.0, 14.1, 12.8, 10.4, 9.3; MS (ESI) m/z calcd. for C49H80N2O15 952.55; found (M+H+) 952.9; Anal. calcd. (%) for C49H80N2O15: C 61.74, H 8.46, N 2.94; found: C 61.71, H 8.44, N 2.96.