Volume 14 Issue 12, December 2022

The direct carbon isotope exchange reaction on α-amino acids is highly desirable, as existing labelling methods require several synthetic steps and harsh conditions. Now, an aldehyde-catalysed carboxylate exchange with isotopically labelled *CO₂ has enabled the direct formation of ¹¹C, ¹³C and ¹⁴C-labelled α-amino acids.

The light-driven conversion of abundant resources such as CO₂ and H₂O into chemical fuels for energy storage is crucial to end our dependence on fossil fuels. This Review highlights how molecular catalysts and photosensitizers can be grafted onto metal–organic frameworks to combine the advantages of both classes of compounds. Different synthetic strategies are discussed, along with their advantages and limitations.

The study of rare isotopes is hampered by their scarcity, cost and sometimes toxicity. Now polyoxometalate ligands have been shown to facilitate the capture of f-block elements and their characterization. Single-crystal X-ray diffraction structures have been obtained for several molecular complexes, including three of the rare curium-248, from minute amounts (micrograms) of material.

Carbon-labelled α-amino acids are valuable compounds in drug development and nuclear medicine, but are difficult and time consuming to prepare. Now, an aldehyde-catalysed method has been developed for the direct C1-labelling of α-amino acids using *CO₂ (* = 14, 13, 11), providing access to many proteinogenic and non-natural labelled α-amino acids.

Native mass spectrometry has been used to interrogate both biased signalling and allosteric modulation of the β₁-adrenergic receptor. Simultaneously capturing the effects of ligand binding and receptor coupling to different G proteins has enabled the relative importance of specific interactions to be investigated.

The properties of chiral conjugated molecules, such as the absorption and/or emission of circularly polarized light or electron transport, are highly anisotropic. Now it has been shown that templating layers can control the orientation and anisotropic properties of small chiral molecules in bulk thin films useful for a range of emerging technologies.

Enteropeptins are peptide natural products produced by the gut microbe Enterococcus cecorum. Now, the structure, biosynthesis and function of enteropeptins have been determined. After ribosomal biosynthesis, enteropeptins are post-translationally modified in three reactions carried out by a radical S-adenosylmethionine enzyme, an Mn²⁺-dependent arginase, and an Fe–S-containing methyltransferase, respectively, to form the N-methylornithine-containing peptide natural products.

Alkyl and aryl polycyanurate networks have now been prepared through polymerization of diols and substituted triazines via a dynamic S_NAr reaction. When treated with excess mono alcohol or phenol, the polycyanurate networks can be depolymerized into the starting monomers, which can be separated and reused, thus achieving closed-loop recycling.

Intersystem crossing in reaction entrance channels usually arises from ‘heavy-atom’ effects. Now molecular-beam experiments show that even without heavy atoms, the O(³P) + pyridine reaction leads to spin-forbidden pyrrole + CO products. Theoretical calculations reveal efficient intersystem crossing before the entrance barrier for O-atom addition to the N-atom lone pair, which dominates reactivity at low to moderate temperatures.

Despite recent advances in engineering of in vitro translation systems, direct ribosomal incorporation of hydroxyhydrocarbon moieties—which can endow peptides with unique biochemical/folding properties—remains challenging. Now, incorporation of translation-compatible azide/hydroxy acids and their post-translational tandem backbone-acyl shifts have enabled in vitro ribosomal synthesis of peptides containing various hydroxyhydrocarbon units.

Tigilanol tiglate is a therapeutic lead for the treatment of a broad range of cancers. Now, it has been shown that tigilanol tiglate can be synthesized in a time and step economical fashion from phorbol—its naturally abundant biosynthetic precursor. This synthesis provides rapid access to analogues with unprecedented protein kinase C binding activity.

Peptide design remains a challenge owing to the large library of amino acids. Rational design approaches, although successful, result in a peptide design bias. Now it has been shown that AI techniques can be used to overcome such bias and discover unusual peptides as efficiently as humans.

Meso–meso linked porphyrin arrays have been described as rod-like photonic wires. Now it has been shown that they can be bent into rings using template-directed synthesis. These rings of porphyrins mimic the light-harvesting arrays of chlorophyll molecules responsible for photosynthesis.

The total synthesis and complete stereochemical assignment of the cyclic peptide natural product SR-A3—which has potential as a cancer therapeutic—has now been reported. Single-molecule biophysical and cellular experiments reveal a crucial, stereospecific role for a side-chain hydroxyl in SR-A3, which confers enhanced target residence time and efficacy in a mouse tumour model.

On-surface synthesis enables highly reactive structures to be produced under vacuum, but they need to be passivated to be incorporated into practical devices. Here, the facile protection of air-sensitive chiral graphene nanoribbons has been shown, by either hydrogenation or synthesis of an oxidized form. The chemically stable forms can subsequently be deprotected.

Methods to access organofluorine compounds with a trifluoromethyl- and fluoro-substituted carbon stereogenic centre are severely limited. Now, a flexible and stereodivergent approach has been developed for the efficient preparation of homoallylic alcohols containing this moiety. Conversion to polyfluoro furanosides and pyranosides has been demonstrated, which is relevant to antiviral drug development.

Abhik Ghosh explores the structure, chemistry and applications of corroles, a class of sterically constrained macrocyclic tetrapyrroles.