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The surface chemistry of Metal-Organic Polyhedra (MOPs) is crucial to their physicochemical properties because it governs how they interact with external substances such as solvents, synthetic organic molecules, metal ions, and even biomolecules. Consequently, the advancement of synthetic methods that facilitate the incorporation of diverse functional groups onto MOP surfaces will significantly broaden the range of properties and potential applications for MOPs. This study describes the use of copper(I)-catalysed, azide-alkyne cycloaddition (CuAAC) click reactions to post-synthetically modify the surface of alkyne-functionalised cuboctahedral MOPs. To this end, a novel Rh(II)-based MOP with 24 available surface alkyne groups was synthesised. Each of the 24 alkyne groups on the surface of the "clickable" Rh-MOP can react with azide-containing molecules at room temperature, without compromising the integrity of the MOP. The wide substrate catalogue and orthogonal nature of CuAAC click chemistry was exploited to densely functionalise MOPs with diverse functional groups, including polymers, carboxylic and phosphonic acids, and even biotin moieties, which retained their recognition capabilities once anchored onto the surface of the MOP.

Homochiral 2-hydroxy-4-butyrolactone derivatives are important structural motifs frequently found in naturally occurring biologically active products, synthetic drugs, biodegradable polymers as well as building blocks and chiral auxiliaries in asymmetric organic synthesis (1). Among the methods described in the literature, the stereoselective reduction of 4-hydroxy-2-oxoacid derivatives to produce 2-hydroxy-4-butyrolactone derivatives remains unexplored. In this communication we report a tandem biocatalytic stereodivergent route for the preparation of these compounds using two stereocomplementary aldolases and oxidoreductases, using simple and achiral starting materials. The strategy comprises (Scheme 1) (i) aldol addition reaction of 2-oxoacids to formaldehyde using both 3-methyl-2-oxobutanoate hydroxymethyltransferase and 2-keto-3-deoxy-L-rhamnonate aldolase and variants thereof, and (ii) subsequent 2-oxogroup reduction of the aldol adduct by both ketopantoate reductase and a delta-1-piperidine-2-carboxylate/delta-1-pyrroline-2-carboxylate reductase with uncovered promiscuous ketoreductase activity. Finally, the formation of the corresponding lactone takes place during the work up and purification steps. Yields, enantiomeric excesses and diasteromeric ratios for a total of 23 structurally diverse 2-hydroxy-3-substituted-4-butyrolactones will be discussed. Moreover, one-pot one-step cascade reactions with the aldolases and reductases operating in tandem will be presented.

NAD(P)H-dependent ¿1-piperideine-2-carboxylate/¿1-pyrroline-2-carboxylate reductase from Pseudomonas syringae pv. tomato (DpkAPsyrin, EC 1.5.1.21) catalyzes the stereoselective reduction of ¿1-piperideine-2-carboxylate and ¿1-pyrroline-2-carboxylate to L-pipecolic acid and L-proline respectively. Furthermore, DpkAPsyrin is also able to catalyze the enantioselective synthesis of N-methyl-L-amino acids from methylamine and various 2-oxo acids [1]. In our research group, we observed that in addition to the imine reductase activity, DpkAPsyrin have a promiscuous ketoreductase activity and, consequently, we consider interesting to exploit its underdeveloped synthetic capabilities for the synthesis of 2-hydroxy-4-arylbut-3-enoic acid (4). These 2-hydroxyacids are intermediates in the synthesis of 2-hydroxy-4-arylbutanoic acid, important building blocks for the production of a variety of angiotensin converting enzyme (ACE) inhibitors (e.g. enalapril, lisinopril, cilapril, and benazepril) [2]. In this communication we reported the preparation of structurally diverse (S)-2-hydroxy-4-arylbut-3-enoic acid (4) (isolated yield: 57%-78% and ee: 87%->99%) from aromatic aldehydes (1) and pyruvate (2) by enzymatic cascade reaction using trans-o-hydroxybenzylidene pyruvate hydratase-aldolase from Pseudomonas putida HBPAPputida) [3] and DpkAPsyrin (Scheme 1). The cascade process was possible because it was found that the ketoreductase preferentially reduced the aldol condensation adducts (3) rather than the pyruvate (2). This allows for high levels of 2-hydroxy-4-arylbut-3-enoic acids (4) conversions ( >95% after 24 h).

Water pollution threatens human and environmental health worldwide. Thus, there is a pressing need for new approaches to water purification. Herein, we report a novel supramolecular strategy based on the use of a metal-organic polyhedron (MOP) as a capture agent to remove nitrogenous organic micropollutants from water, even at very low concentrations (ppm), based exclusively on coordination chemistry at the external surface of the MOP. Specifically, we exploit the exohedral coordination positions of RhII-MOP to coordinatively sequester pollutants bearing N-donor atoms in aqueous solution, and then harness their exposed surface carboxyl groups to control their aqueous solubility through acid/base reactions. We validated this approach for removal of benzotriazole, benzothiazole, isoquinoline, and 1-napthylamine from water.