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In order to put the previously proposed concept of directed evolution of hybrid catalysts (proteins that harbor synthetic transition-metal catalysts or organocatalysts) into practice, several prerequisites must be met. The availability of a robust host protein that can be expressed in sufficiently large amounts, and that can be purified in a simple manner is crucial. The thermostable enzyme tHisF from Thermotoga maritima, which constitutes the synthase subunit of a bi-enzyme complex that is instrumental in the biosynthesis of histidine, fulfills these requirements. In the present study, fermentation has been miniaturized and parallelized, as has purification of the protein by simple heat treatment. Several mutants with strategically placed cysteines for subsequent bioconjugation have been produced. One of the tHisF mutants, Cys9Ala/Asp11Cys, was subjected to bioconjugation by the introduction of a variety of ligands for potential metal ligation, of a ligand/metal moiety, and of several organocatalytic entities that comprise a flavin or thiazolium salts. Characterization by mass spectrometry and tryptic digestion was achieved. As a result of this study, a platform for performing future directed evolution of these hybrid catalysts is now available.

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Abstract. Herein, we report a detailed study on the electrophilic alkynylation of cyclic keto-esters and amides with ethynylbenziodoxolone (EBX) reagents. The structure and stability of this class of reagents is first described more in details. DSC experiments showed a strong exothermic decomposition with EBX reagents, leading to guidelines for the safe use of these compounds. The extension of the method to aromatic alkynes and a broad range of benziodoxol(on)e reagents is then reported. Based on our preliminary results using cinchona-based phase-transfer catalysts, the enantioselective alkynylation of cyclic keto-esters could be achieved. Binaphthyl-derived ammonium catalysts developed by Maruoka and co-workers gave the highest asymmetric induction with up to 79% ee for an indanone-derived keto-ester.Throughout this work, asymmetric induction was observed only in the case of benziodoxolone reagents, demonstrating their superiority over conventional alkynyliodonium salts. The deeper understanding gained about the factors leading to higher asymmetric induction will be very useful in the future to develop a truly general and highly enantioselective alkynylation method.

New oligomers or polymers are prepared by polymerization of arsonium ylides in the presence of boron compounds.

Promiscuous reactions get around: It is shown that promiscuous enzyme‐catalyzed reactions (i.e., the catalysis of distinctly different chemical transformations) can also take place at sites other than where the natural reaction occurs.

The polymerization of several allylic triphenylarsonium ylides, which contain a pendant R group at the 2-position, in the presence of triethylborane, is described. Three initial molar ratios of ylide to triethylborane (15, 30, 60) were used, leading to different degrees of polymerization. The ylide was generated from the corresponding arsonium salt, in THF at −78 °C, using either tert-butyllithium (when R = alkyl) or lithium hexamethyldisilazide (when R = tBuMe2SiOCH2CH2−) as the base. After addition of triethylborane at 0 °C, the deep-red solution of ylide was readily discolored. Then oxidation of the resulting polymeric borane led to linear skipped polyenes containing a terminal alcohol function. These polymers can be called poly(2-substituted-1-propenylene)s. Molecular weights have been determined from both 1H NMR analyses and size exclusion chromatography (SEC). In most cases, the molecular weight of the polymers increases linearly with the initial ylide/triethylborane molar ratio, which gives credit to a controlled polymerization process. Block copolymers were also obtained from triethylborane by successive additions of two different 2-substituted allylic arsonium ylides, followed by oxidation (yield:  62−85%).

A systematic investigation of structural modifications of brassinosteroids is presented. We describe in detail their synthetic preparation, which includes significant improvements of previously reported protocols as well as access to new analogs with functional modifications of the steroid skeleton and of the C(17)‐attached side chain. We report the biological potency of the prepared brassinosteroid analogs as plant hormones, which were carefully established in the French bean second internode elongation assay and discuss our observations in light of the recently reported structural data detailing the molecular interactions between brassinolide in the trimeric complex with the protein receptors kinases BRASSINOSTEROID INSENSITIVE 1 (BRI1) and SOMATIC EMBRYOGENESIS RECEPTOR KINASE 1 (SERK1). In a further part of this work we describe the preparation of H2O‐soluble pro‐forms of 24‐epicastasterone and we discuss their physical properties, hydrolytic stabilities and biological activity.