Current Organic Chemistry - Volume 20, Issue 24, 2016

The asymmetric hydrogenation of C=C, C=N and C=O bonds catalyzed by chiralligand modified transition metal complexes is a very important process for the organic synthesis and fine chemical production. & A large number of hydrogenation chiral catalysts mainly based on transition metals such as rhodium, ruthenium and iridium have been successfully developed. & Even though outstanding results have been achieved in this area, so far relatively few catalysts for asymmetric hydrogenation have been applied to fine chemical industry [5-6]. Thus, many efforts are being made to rationally design highly active catalysts with a broad substrate scope. & In the last few years, less expensive catalysts based on transition metals such as cobalt, copper, iron and palladium have afforded promising results. & This review reports on the most relevant chiral catalysts for asymmetric hydrogenation of C=C, C=N and C=O bonds that were published from 2005 up today.

Currently, dendrimers are molecules widely investigated due to their strong potential for biomedical (including diagnostic, drug discovery, and drug delivery platforms) and others applications. The requirements demanded by Food and Drug Administration (FDA) of a new drug application involve several analytical techniques for characterization, which allow understanding the properties of the novel platforms, and to predict their interactions with the biological environment. This work proposes a full description to perform the analytical characterization of dendrimers, including techniques for evaluating the morphology, shape, molecular weight, polydispersity, and purity; as well as methods for the synthesize and conjugation with molecules for targeting.

The cyclofunctionalization reactions promoted by electrophilic selenium species are undoubtedly very powerful methodologies in organic chemistry for the construction of different oxygen- and nitrogen-containing heterocycles. If alkene is bearing suitably oriented internal nucleophile, such as OH, COOH, NHR, a variety of heterocyclic compounds, such as ethers, lactones, pyrolidines, piperidines can be synthesized by the usage of this extremely useful synthetic protocol. In the last decade great progress had been done in the field of selenium promoted ring closure reactions by the means of selectivity, efficiency in asymmetric synthesis and simplicity of the procedure. Vast variety of heterocyclic products that can be prepared by this method, combined with its other advantages, has inspired its utilization in some total synthesis of naturally occurring compounds which have nitrogen or oxygen heterocycles as scaffolds in their structures. Our review is focused on broad possibilities of electrophilic selenocyclofunctionalization protocol as decisive and important stage in the total synthesis of biologically important molecules.

Mushrooms have an acclaimed history of therapeutic use in traditional medicine. The prevalent occurrence of infectious diseases is becoming a worldwide problem, due to bacterial resistance against antimicrobial drugs which have been long used for therapeutic and prophylactic purposes. For this reason, the search has intensified for natural sources with antimicrobial activity. The literature contains scientific data about the high antimicrobial activity of mushrooms against Gram-positive and Gram-negative bacterial species. In this review we have focused on compounds obtained from mushrooms which exhibit antimicrobial activity, commonly used methods for evaluation of antimicrobial activity and last but not least on syntheses of some selected compounds originally isolated from mushrooms.

A cinchona-catalysed, enantioselective oxa-Michael reaction of α,β-unsaturated aldehydes with either tert-butyl hydroperoxide or cumene hydroperoxide was developed. The reaction was optimised by screening of solvents, modification of the catalyst framework and variation of the acid co-catalysts. A strong relationship was noted between the pKa of the acid co-catalyst and the degree of selectivity. Enantioselective peroxidation of α,β- unsaturated aldehydes with tert-butyl hydroperoxide afforded β-peroxyaldehydes with good enantioselectivities. In situ oxidation of the latter compounds furnished β-peroxycarboxylic acids in high yields. Enantiomeric excesses were determined by derivitisation to their mandelate esters and subsequent separation by chiral high performance liquid chromatography. Peroxidation with cumene hydroperoxide was similarly successful with the products being isolated as stable β-peroxyalcohols. These latter β-peroxyalcohols offer a direct route to 5-membered, chiral cycloperoxides via a silver-mediated cyclisation. This reaction proceeds by trapping of the oxygen lone pair by the incipient carbocation followed by loss of the cumyl or tert-butyl group and formation of the cycloperoxide product.

Halogenation reactions of vindoline and 14,15-dihydrovindoline and its hydrochloric salt were investigated and the anomalous reductions were discussed. Performing the hydrogenation in the presence of chlorine-containing solvent, e.g. dichloromethane, hydrogenolysation reaction of chlorine also took place. In this case unexpected chlorinated product could be observed. Performing the hydrogenation reaction only in the presence of methanol, the expected reduced derivative was obtained. Upon bromination of vindoline with excess NBS, oxidation products with ring contraction and developing an oxygen bridge were isolated. The fluorination reactions of vinblastine using Selectfluor® and xenon difluoride as the fluorination reagents were unsuccessful because of the decomposition of the starting material. Reactions of vindoline with Selectfluor® a mixture of products were obtained. Using xenon difluoride as fluorination agent resulted in a pure quinoidal product containing the fluorine atom in the bridgehead carbon atom of the indole ring. The fluorination of catharanthine gave an anomalous indolenine type product.