α-Pyrone derivatives with cyto-protective activity from two Takla Makan desert soil derived actinomycete Nocardiopsis strains recovered in seawater based medium

In this paper, we described the discovery of two Nocardiopsis strains HDN154-146 and HDN154-168 from Takla Makan desert soil samples using seawater based medium. Chemical investigation of these two strains led to the discovery of eight new α-pyrone derivatives named nocahypyrones A-H (1–8), together with one known analogue germicidin G (9). The structures of these compounds, including absolute configurations, were elucidated by extensive NMR, MS, and CD analyses. Compounds 1–9 were tested for their cyto-protective activities and for the first time we found α-pyrones 5 and 8 exhibited capabilities to induce expression of phase II detoxifying enzymes.     

α-glucosidase inhibitors isolated from Mimosa pudica L.

The aim of the study was to isolate digestive enzymes inhibitors from Mimosa pudica through a bioassay-guided fractionation approach. Repeated silica gel and sephadex LH 20 column chromatographies of bioactive fractions afforded stigmasterol, quercetin and avicularin as digestive enzymes inhibitors whose IC₅₀ values as compared to acarbose (351.02 ± 1.46 μg mL^?1) were found to be as 91.08 ± 1.54, 75.16 ± 0.92 and 481.7 ± 0.703 μg mL^?1, respectively. In conclusion, M. pudica could be a good and safe source of digestive enzymes inhibitors for the management of diabetes in future.     

Hydroxyapatite For Poly(α-Hydroxy Esters) Biocomposites Applications

This article focuses on providing a systematic review on various fundamental properties of composite based on poly(α-hydroxy esters) and hydroxyapatite (HAp) for application in bone tissue engineering. Poly(α-hydroxy esters), a well-known synthetic biopolymer has attracted considerable interest to be employed for synthesis of bone graft substitute material with HAp mainly due to its bioresorbability, variable biodegradation rate and melt-processibility. Such features are simultaneously attractive for both biomedical application and industrial-scale productions. Besides the main function of hydroxyapatite as bioactive ceramic filler in composite to induce new bone formation upon polymer bioresorption, HAp can also serve as reinforcement for matrix polymer by providing sufficient mechanical support for cell attachment. Moreover, HAp plays a significant role in determining other composite properties, such as resistance to ingress of body fluid, body temperature ageing, relaxation movement of polymer segment, and in vivo biodegradation. These properties constitute as the fundamental requirements in field of bone tissue regeneration which is desirable to be achieved by unique composite system based on poly(α-hydroxyesters) and HAp particles.     

The asymmetric synthesis of (S,S)-methylphenidate hydrochloride via ring-opening of an enantiopure aziridinium intermediate with phenylmagnesium bromide

The key step in our synthetic strategy towards (S,S)-methylphenidate hydrochloride employs the ring-opening of an in situ formed aziridinium intermediate. Treatment of an α-hydroxy-β-amino ester with methanesulfonic anhydride promoted aziridinium formation and the subsequent addition of phenylmagnesium bromide resulted in stereospecific and regioselective ring-opening to give the corresponding α-phenyl-β-amino ester with overall retention of configuration. Subsequent functional group manipulation followed by N-deprotection and cyclisation generated the piperidine ring within the target compound, and transesterification gave (S,S)-methylphenidate hydrochloride, in only 8 steps from 1,5-pentanediol, in 15% overall yield. These results demonstrate the synthetic utility of enantiopure aziridinium intermediates as substrates for the generation of stereodefined C–C bonds, and crucially this methodology provides access to α-substituted-β-amino ester substrates that are not accessible via enolate alkylation chemistry. The strategy reported herein is potentially applicable to all possible stereoisomers of methylphenidate as well as differentially substituted analogues.     

Copper-catalyzed synthesis of gem-difluoroallylboronates from α-trifluoromethyl alkenes and B2pin2

A novel and efficient method for the synthesis of gem-difluoroallylboronates via copper-catalyzed defluorinative borylation of α-trifluoromethyl alkenes with B₂pin₂ using Xantphos as ligand and NaOtBu as base was developed.     

Heterogeneous gold-catalyzed oxidative cross-coupling of propargylic acetates with arylboronic acids leading to (E)-α-arylenones

An efficient heterogeneous gold-catalyzed oxidative cross-coupling of propargylic acetates with arylboronic acids has been developed that proceeds smoothly in the presence of Selectfluor and provides a general and powerful tool for the preparation of various valuable α-arylenones with moderate to good yields, excellent E-selectivity, and recyclability of the gold catalyst. The reaction is the first example of heterogeneous gold-catalyzed arylative rearrangement of propargylic acetates for construction of complex enones.     

Palladium-catalyzed carbonylative/decarboxylative cross-coupling of α-bromo-ketones with allylic alcohols to γ,δ-unsaturated ketones

In this communication, a palladium-catalyzed carbonylative/decarboxylative cross-coupling of α-bromo-ketones with allylic alcohols has been developed. With Mo(CO)₆ as the CO source, γ,δ-unsaturated ketones were isolated in good yields. The release of CO₂ was confirmed as well.     

Three-step synthesis of oxylipins from D. loretense

A three-step convergent synthesis of an immunostimulatory oxylipin was developed using an olefin cross metathesis approach. The alkene fragments were prepared in two steps from commercially available starting materials with high stereoselectivity. In particular, an organocatalytic aldehyde α-oxygenation gave high enantioselectivity and yield using as little as 2 mol% catalyst. This synthesis represents the shortest synthesis of any natural product containing the 3-ene-1,2,5-triol moiety and delivers an immunostimulatory oxylipin in 33% overall yield.     

Highly adequate oxidative esterification of α-carbonyl aldehydes with alkyl halides in TBAI/TBHP mediated system

An efficient and viable synthesis of α-ketoesters from alkyl halides and α-carbonyl aldehydes has been reported under metal-free conditions. The present method involves oxidative esterification of α-carbonyl aldehydes with alkyl halide using TBAI as a promoter and TBHP as an oxidant to form α-ketoesters in good to excellent yields with versatile structural diversity. Use of commercially accessible and inexpensive substrates, broad substrate scope and good functional group tolerance are the key features of this protocol.     

Asymmetric organocatalytic cascade Michael/acyl transfer reaction of 2-hydroxychalcones with α-nitroketones

A highly enantioselective (84–97% ee) cascade Michael/acyl transfer reaction of α-nitroketones to a wide range of 2-hydroxychalcones was established in the presence of a bifunctional squaramide. Although aliphatic α-nitroketones were revealed to be a class of challenging substrates with unsatisfactory reactivity or enantioselectivity by previous reports, good isolated yields and excellent enantiopurities have been achieved via our catalytic protocol. γ-Nitroketones created by this new methodology were versatile building blocks possessing profound further synthetic utility.