Synthesis of rare sugar isomers through site-selective epimerization


Glycans have diverse physiological functions, ranging from energy storage and structural integrity to cell signalling and the regulation of intracellular processes1. Although biomass-derived carbohydrates (such as d-glucose, d-xylose and d-galactose) are extracted on commercial scales, and serve as renewable chemical feedstocks and building blocks2,3, there are hundreds of distinct monosaccharides that typically cannot be isolated from their natural sources and must instead be prepared through multistep chemical or enzymatic syntheses4,5. These ‘rare’ sugars feature prominently in bioactive natural products and pharmaceuticals, including antiviral, antibacterial, anticancer and cardiac drugs6,7. Here we report the preparation of rare sugar isomers directly from biomass carbohydrates through site-selective epimerization reactions. Mechanistic studies establish that these reactions proceed under kinetic control, through sequential steps of hydrogen-atom abstraction and hydrogen-atom donation mediated by two distinct catalysts. This synthetic strategy provides concise and potentially extensive access to this valuable class of natural compounds.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Approaches to the epimerization of sugars.
Fig. 2: Epimerization of α-methylglucose to α-methylallose.
Fig. 3: Site-selective epimerization of saccharides and glycans.
Fig. 4: Mechanistic studies and proposed mechanism.

Data availability

All data supporting the findings of this paper are available within the Article and its supplementary information files.


  1. 1.

    Varki, A. et al. (eds) Essentials of Glycobiology 3rd edn (Cold Spring Harbor Laboratory Press, 2017).

  2. 2.

    de Leder Kremer, R. M. & Gallo-Rodriquez, C. Naturally occurring monosaccharides: properties and synthesis. Adv. Carbohydr. Chem. Biochem. 59, 9–67 (2004).

  3. 3.

    Chheda, J. N., Huber, G. W. & Dumesic, J. A. Liquid-phase catalytic processing of biomass-derived oxygenated hydrocarbons to fuels and chemicals. Angew. Chem. Int. Ed. 46, 7164–7183 (2007).

  4. 4.

    Imperiali, B. Bacterial carbohydrate diversity—a brave new world. Curr. Opin. Chem. Biol. 53, 1–8 (2019).

  5. 5.

    Herget, S. et al. Statistical analysis of the Bacterial Carbohydrate Structure Data Base (BCSDB): characteristics and diversity of bacterial carbohydrates in comparison with mammalian glycans. BMC Struct. Biol. 8, 35 (2008).

  6. 6.

    Frihed, T. G., Bols, M. & Pedersen, C. M. Synthesis of l-hexoses. Chem. Rev. 115, 3615–3676 (2015).

  7. 7.

    Elshahawi, S. I., Shaaban, K. A., Kharel, M. K. & Thorson, J. S. A comprehensive review of glycosylated bacterial natural products. Chem. Soc. Rev. 44, 7591–7697 (2015).

  8. 8.

    Angyal, S. The Lobry de Bruyn–Albereda van Ekenstein transformation and related reactions. In Glycoscience: Epimerisation, Isomerisation and Rearrangement Reactions of Carbohydrates (ed. Stütz, A. E.) 1–14 (Springer, 2001).

  9. 9.

    Buchholz, K. & Seibel, J. Industrial carbohydrate biotransformations. Carb. Res. 343, 1966–1979 (2008).

  10. 10.

    Bhosale, S. H., Rao, M. B. & Deshpande, V. V. Molecular and industrial aspects of glucose isomerase. Microbiol. Rev. 60, 280–300 (1996).

  11. 11.

    Wulf, P. & Vandamme, E. Production of d-ribose by fermentation. Appl. Microbiol. Biotechnol. 48, 141–148 (1997).

  12. 12.

    Granström, T. B., Takata, G., Tokuda, M. & Izumori, K. Izumoring: a novel and complete strategy for the bioproduction of rare sugars. J. Biosci. Bioeng. 97, 89–94 (2004).

  13. 13.

    Zhang, W., Zhang, T., Jiang, B. & Mu, W. Enzymatic approaches to rare sugar production. Biotechnol. Adv. 35, 267–274 (2017).

  14. 14.

    Hossain, M. A. et al. Effect of the immunosuppressants FK506 and d-allose on allogenic orthotopic liver transplantation in rats. Transplant. Proc. 32, 2021–2023 (2000).

  15. 15.

    Menavuvu, B. T. et al. Efficient biosynthesis of d-allose from d-psicose by cross-linked recombinant l-rhamnose isomerase: separation of product by ethanol crystallization. J. Biosci. Bioeng. 101, 340–345 (2006).

  16. 16.

    Kudo, F., Hoshi, S., Kawashima, T., Kamach, T. & Eguchi, T. Characterization of a radical S-adenosyl-l-methionine epimerase, NeoN, in the last step of neomycin B biosynthesis. J. Am. Chem. Soc. 136, 13909–13915 (2014).

  17. 17.

    Benjdia, A., Guillot, A., Ruffie, P., Leprince, J. & Berteau, O. Post-translational modification of ribosomally synthesized peptides by a radical SAM epimerase in Bacillus subtilis. Nat. Chem. 9, 698–707 (2017).

  18. 18.

    Wang, Y. et al. Epimerization of tertiary carbon centers via reversible radical cleavage of unactivated C(sp 3)–H bonds. J. Am. Chem. Soc. 140, 9678–9684 (2018).

  19. 19.

    Shin, N. Y., Ryss, J. M., Zhang, X., Miller, S. J. & Knowles, R. R. Light-driven deracemization enabled by excited-state electron transfer. Science 366, 364–369 (2019).

  20. 20.

    Dimakos, V. & Taylor, M. S. Site-selective functionalization of hydroxyl groups in carbohydrate derivatives. Chem. Rev. 118, 11457–11517 (2018).

  21. 21.

    Frihed, T. G., Bols, M. & Pedersen, C. M. C–H functionalization on carbohydrates. Eur. J. Org. Chem. 2740–2756 (2016).

  22. 22.

    Jäger, M., Hartmann, M., de Vries, J. G. & Minnaard, A. J. Catalytic regioselective oxidation of glycosides. Angew. Chem. Int. Ed. 52, 7809–7812 (2013).

  23. 23.

    Chung, K. & Waymouth, R. M. Selective catalytic oxidation of unprotected carbohydrates. ACS Catal. 6, 4653–4659 (2016).

  24. 24.

    Muramatsu, W. Catalytic and regioselective oxidation of carbohydrates to synthesize keto-sugars under mild conditions. Org. Lett. 16, 4846–4849 (2014).

  25. 25.

    Wan, I. C., Witte, M. D. & Minnaard, A. J. Site-selective carbon–carbon bond formation in unprotected monosaccharides using photoredox catalysis. Chem. Commun. 53, 4926–4929 (2017).

  26. 26.

    Dimakos, V., Su, H. Y., Garrett, G. E. & Taylor, M. S. Site-selective and stereoselective C–H alkylations of carbohydrates via combined diarylborinic acid and photoredox catalysis. J. Am. Chem. Soc. 141, 5149–5153 (2019).

  27. 27.

    Maiti, N. C., Zhu, Y., Carmichael, I., Serianni, A. S. & Anderson, A. E. 1JCH correlates with alcohol hydrogen bond strength. J. Org. Chem. 71, 2878–2880 (2006).

  28. 28.

    Goldberg, R. N. & Tewari, Y. B. Thermodynamic and transport properties of carbohydrates and their monophosphates: the pentoses and hexoses. J. Phys. Chem. Ref. Data 18, 809–880 (1989).

  29. 29.

    Jeffrey, J. L., Terrett, J. A. & Macmillan, D. W. C. O–H hydrogen bonding promotes H atom transfer from α C–H bonds for C–alkylation of alcohols. Science 349, 1532–1536 (2015).

Download references


We thank A. Seim for checking the reaction procedure and X. Gu for help with substrate synthesis. A.E.W. also thanks E. Kwan, A. Radosevich, D. Suess and Z. Wickens for discussions. Financial support for this work was provided by the Massachusetts Institute of Technology and the National Science Foundation (NSF) for funding through the National Science Foundation Graduate Research Fellowships Program (NSF-GRFP) to H.M.C.

Author information

A.E.W. and Y.W. conceived the work. A.E.W., Y.W. and H.M.C. designed the experiments. Y.W. and H.M.C. conducted the experiments. A.E.W. directed the research and wrote the manuscript with input from all authors.

Correspondence to Alison E. Wendlandt.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature thanks Christian Marcus Pedersen and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data figures and tables

Extended Data Fig. 1 Chemical and enzymatic isomerizations proceed through polar aldose-ketose mechanisms.

a, Chemical isomerization reactions of glucose lead to unselective and complex thermodynamic distribution of products. b, ‘Izumoring’ enzymatic synthesis of d-allose proceeds through reversible polar enolization mechanisms under equilibrium control; see ref. 12. d-XI is d-xylose isomerase; d-TE is d-tagatose 3-epimerase; and l-RhI is l-rhamnose isomerase.

Supplementary information

Supplementary Information

This file contains the following sections: 1. General Experimental Methods; 2. Materials and Reagents; 3. Instrumentation; 4. Synthesis of Catalysts (4CzIPN and 4-ClOBzBu4N) and Substrates; 5. General Reaction Procedure for Sugar Epimerization; 6. General Procedure for Purification of Epimeric Sugars; 7. Product Characterization; 8. Condition Optimization for Sugar Epimerization of 1a; 9. Mechanistic Studies; 10. References; and 11. NMR Spectra.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Wang, Y., Carder, H.M. & Wendlandt, A.E. Synthesis of rare sugar isomers through site-selective epimerization. Nature 578, 403–408 (2020).

Download citation

Further reading

  • Notizen aus der Chemie

    • Johanna Heine
    • , Alexander Hinz
    • , Constantin Hoch
    • , Ullrich Jahn
    • , Stefan Knecht
    • , Hajo Kries
    • , Björn Meermann
    • , Hatice Mutlu
    • , Andreas Schnepf
    •  & Erik Strub

    Nachrichten aus der Chemie (2020)


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.