A structure-antifungal activity relationship (SAR) study of 22 related cinnamic acid derivatives was carried out. Attention was focused on the antifungal activities exhibited against Aspergillus flavus, Aspergillus terreus, and Aspergillus niger. (E)-3-(4-methoxy-3-(3-methylbut-2-enyl)phenyl)acrylic acid (16) exhibited antifungal activity against A. niger, comparable to that of miconazole and a significant antifungal effect against A. flavus and A. terreus as well. A structure-activity relationship (SAR) study of related cinnamic acid derivatives has allowed a model to be proposed for the recognition of the minimal structural requirements for the antifungal effect in this series.
As part of our studies on the biochirogenesis of peptides of homochiral sequence during early evolution, the formation of oligopeptides composed of 14-24 residues of the same handedness in the polymerization of dl-leucine (Leu), dl-phenylalanine (Phe), and dl-valine (Val) in aqueous solutions, by activation with N, N'-carbonyldiimidazole and then initiation with a primary amine, in a one-pot reaction, was demonstrated by MALDI-TOF MS using deuterium enantio-labeled alpha-amino acids. The formation of long isotactic peptides is rationalized by the following steps occurring in tandem: (i) creation of a library of short diasteroisomeric oligopeptides containing isotactic peptides in excess in comparison to a binomial kinetics, as a result of an asymmetric induction exerted by the N-terminal residue of a given handedness; (ii) precipitation of the less soluble racemic isotactic penta- and hexapeptides in the form of beta-sheets that are delineated by homochiral rims; (iii) regio-enantiospecific chain elongation occurring heterogeneously at the beta-sheets/solution interface. Polymerization of l-Leu with l-isoleucine (Ile) or l-Phe with l- (1) N-Me-histidine yielded mixtures of copeptides containing both residues. In contrast, in the polymerization of the corresponding mixtures of l- + d-alpha-amino acids, the long oligopeptides were composed mainly from oligo- l-Leu and oligo- d-Ile in the first system and oligo- d-Phe in the second. Furthermore, in the polymerization of mixtures of hydrophobic racemic alpha-amino acids dl-Leu, dl-Val, and dl-Phe and with added racemic dl-alanine and dl-tyrosine, copeptides of homochiral sequences are most dominantly represented. Possible routes for a spontaneous "mirror-symmetry breaking" process of the racemic mixtures of homochiral peptides are presented.
A novel one-pot tandem biohydrogen transfer process to concurrently obtain two enantiopure sec-alcohols is presented; thus, using a suitable single enzyme and a catalytic amount of cofactor, several interesting building blocks could be easily achieved in an enantiocomplementary fashion, minimizing dramatically the quantity of reagents usually employed in the “coupled-substrate” approach.
Simple and quick preparation of α-thiocyanate ketones in hydroalcoholic media. Access to 5-aryl-2-imino-1,3-oxathiolanes A simple preparation on gram-scale of thiocyanate derivatives via nucleophilic substitution of halogenated compounds with SCN salts at high substrate concentrations in a few minutes and excellent yields was successfully accomplished in hydroalcoholic media. The obtained compounds were employed for the efficient synthesis of valuable 5-aryl-2-imino-1,3-oxathiolane derivatives (a one-pot approach is also presented).In the last few years, sustainable processes are highly demanded in the chemical industry.1 The "process efficiency"concept is not only related to a high chemical yield, but also to the minimised use of large amounts of harmful organic solvents and production of chemical waste. have been shown. Finally, the formation of β-hydroxy thiocyanates via oxirane ring-opening with NH 4 SCN has been described. 21 In most cases, several reagents, organic solvents and high temperatures were employed, and therefore purification by chromatography was necessary. This is in contrast with the optimum conditions to synthesise these compounds since the isomerisation thiocyanate-isothiocyanate can occur in solution at temperatures above 50ºC and/or acidic conditions. 10,16,22 For these reasons, the development of new procedures for the easy and rapid synthesis of thiocyanate derivatives in high yields is required. Herein we report our efforts in the preparation of versatile thiocyanate compounds in aqueous mixtures at high substrate concentrations and further conversion into the interesting heterocyclic 2-imino-1,3-oxathiolane system employing mild reaction conditions and cheap reagents.
Abstract:In order to ensure the quasiirreversibility of the oxidation of alcohols coupled with the reduction of ketones in a hydrogen transfer (HT) fashion, stoichiometric amounts of α-halo carbonyl compounds as hydrogen acceptors have been employed. The reason why these substrates lead to quasi-quantitative conversions has been tacitly attributed to both thermodynamic and kinetic effects. In order to provide a clear rationale for this behavior, we study here the redox equilibrium of a selected series of ketones and 2-propanol by undertaking an approach that combines experimental and theoretical elements.
Multi‐step processes catalysed by several catalysts working concurrently have been developed in nature, thus improving reaction efficiency. The quest for novel and improved catalytic systems has led to the development of biocatalytic and later to organocatalytic procedures as very valuable tools in asymmetric synthesis while using mild reaction conditions in the absence of metal catalysts. As a timeless challenge, chemists are facing the need for process designs in which different sorts of catalysts can operate successfully in a one‐pot concurrent fashion. Likewise, such designs bring about the best of each catalyst and, in certain cases, enable us to improve problematic issues, such as reactivity, selectivity, solubility, inhibition, etc. Specifically, to combine these two types of catalysts in one‐pot, achieving high yields and selectivity, is a fascinating aspect of catalysis. This review covers representative advances in this field, in particular those in which biocatalysts and organocatalysts are employed either in sequential reactions or in simultaneous processes.
Abstract. α-Alkyl-β-hydroxyesters were obtained via DKR employing purified or crude E. coli overexpressed alcohol dehydrogenases (ADHs). ADH-A from R. ruber, CPADH from C. parapsilosis and TesADH from T. ethanolicus afforded syn-(2R,3S) derivatives with very high selectivities for sterically not impeded ketones ('small-bulky' substrates), while ADHs from S. yanoikuyae (SyADH) and Ralstonia sp. (RasADH) could also accept bulkier ketoesters ('bulkybulky' substrates). SyADH also provided preferentially syn-(2R,3S) isomers and RasADH showed in some cases good selectivity towards the formation of anti-(2S,3S) derivatives.With anti-Prelog ADHs such as LBADH from L. brevis or LKADH from L. kefir, syn-(2S,3R) alcohols were obtained with high conversions and diastereomeric excess in some cases, especially with LBADH. Furthermore, due to the thermodynamically favoured reduction of these substrates, it was possible to employ just a minimal excess of 2-propanol to obtain the final products with quantitative conversions.
Abstract. Regio-and stereoselective reductions of several diketones to afford enantiopure hydroxy ketones or diols were accomplished using isolated alcohol dehydrogenases (ADHs). Results could be rationalised taking into account different (promiscuous) substrate-binding modes in the active site of the enzyme. Furthermore, interesting natural cyclic diketones were also reduced with high regio-and stereoselectivity.Some of the 1,2-and 1,3-diketones used in this study were reduced employing a low excess of the hydrogen donor (2-propanol) due to the quasi-irreversibility of these ADHcatalysed processes. Thus, using less quantity of cosubstrate, scale-up could be easily achieved.
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