Synthesis of a spiroacetal moiety of antitumor antibiotic ossamycin by anodic oxidation

Synthesis of the spiroacetal moiety (C20-C33) of the antitumor antibiotic ossamycin, is reported. Anodic oxidation of the dithioacetal effected simultaneous removal of the protecting group and acetalization to afford the corresponding 6,6-spiroacetal structure in excellent yield.     

Optical evodiamine derivatives:Asymmetric synthesis and antitumor activity

Evodiamine and its derivatives have an asymmetric center at the C13 b position.Herein,isomers of evodiamine derivatives 2 and 3 were obtained by straightforward asymmetric total synthesis.Their inhibitory activities toward topoisomerases I and II and their cytotoxicities in cancer cell lines were evaluated.All the four isomers exhibited good to excellent antitumor potency and the(S)-isomers were generally more active than the(R)-isomers.The binding modes of(S)-2 with topoisomerases I and II were also clarified by molecular docking.     

Asymmetric synthesis of furofurans

Furofurans are one of the largest sub-types of classical lignans which have been found to possess a broad range of important biological activities. Tremendous efforts have been directed to develop synthetic methodologies for the synthesis of furofurans, especially in a stereoselective manner, due to their interesting bioactivities associated with the structural and stereochemical complexity. This article summarizes the reports on asymmetric synthesis of furofurans disclosed during the period of 2004–2017.     

2-[二-(2-氯乙基)-胺基]-5-苄氧基-1,3,2-氧氮磷杂环己烷-2-氧化物的不对称合成

2-[二-(2-氯乙基)-胺基]-5-苄氧基-1,3,2-氧氮磷杂环己烷-2-氧化物是抗癌药物Endoxan的衍生物,其光学异构体的合成已有报道.本文报道了我们从廉价易得的手性原料天然-L-酒石酸开始,通过较为简捷的合成路线,完成了对目标化合物全部4个光学异构体的合成.化合物的有关数据参见表1.     

Asymmetric synthesis of 3,3-disubstituted isoindolinones

An anionic chiral auxiliary-mediated asymmetric alkylation of carbamate 2 affords 3,3-disubstituted isoindolinones 3 in moderate to high de. The chiral auxiliary can be removed and recovered under mild conditions, and the resulting enantiopure lactams further elaborated.     

Studies toward asymmetric synthesis of leiodelide A

An enantioselective route for oxazoline 4, a key fragment toward the asymmetric synthesis of leiodelide A, is described. We synthesized northern subunit 6 through a Julia–Lythgoe olefination and subsequent Sharpless asymmetric dihydroxylation. Moreover, a highly diastereoselective method using well-established Evans’ asymmetric aldol condensation was developed for preparation of southern fragment 5. The additional feature of this synthetic route is the formation of oxazoline 4 through DAST-promoted cyclization of the amidation product from subunits 5 and 6.     

Asymmetric Total Synthesis of Fredericamycin A

Seventeen years after the isolation of the promising antitumor antibiotic fredericamycin A, the first asymmetric total synthesis of this compound has been accomplished and thereby its absolute configuration established. The key feature is the regiocontrolled [4+2] cycloaddition of 3 to 2 , which was obtained by the stereospecific rearrangement of 1 . Cp = (−)‐camphanoyl.     

Asymmetric synthesis of all the stereoisomers of tarchonanthuslactone

We describe herein an efficient synthesis of all the four stereoisomers of tarchonanthuslactone from (R)-3-hydroxy butanoate, easily prepared from l-threonine. The approach involves the use of a β,γ-unsaturated δ-lactone as an intermediate, obtained via a Kulinkovich reaction followed by a ring-closing metathesis strategy.     

Asymmetric synthesis of (+)-chloriolide

An asymmetric synthesis of 12-membered ring macrolide, chloriolide has been accomplished by adopting a linear strategy. Lipase-catalyzed enzymatic kinetic resolution (EKR), asymmetric alkynylation using Trost pro-phenol catalyst followed by Yamaguchi macrolactonization has been successfully employed to achieve the target molecule.     

Reversed-phase HPLC analysis of the semisynthetic macrolide antibiotic azithromycin

Summary HPLC is the most convenient method for the assay of the azithromycin (10-dihydro-10-deoxo-11-methyl-11-azaerythromycin A), a semisynthetic macrolide antibiotic and its reaction intermediates. Data concerning the effects of pH, temperature and column type are presented. The analytical procedures enabling the reliable assay of azithromycin and its intermediates, as well as other impurities are defined. Use of a reversed-phase octadecyl column, a pH of 9.3–9.5, and isocratic mode at ambient temperature are the best conditions of analysis.     

Asymmetric synthesis of 2-substituted cyclic amines

Cyanomethylenetributylphosphorane-mediated ring closure for the asymmetric synthesis of 2-substituted cyclic amines such as azetidines, pyrrolidines and a piperidine is reported. The desired stereochemistry at the 2-position was fixed using (S)-tert-butyl sulfinamide as a chiral auxiliary.     

Asymmetric synthesis of an aminomethyl morpholine via double allylic substitution

The development of an asymmetric route to an aminomethyl morpholine intermediate via palladium-catalysed allylic substitution is described.     

Toward the synthesis of macrolide aspergillide D

Stereoselective synthesis of 16-membered macrocyclic core of marine natural product, Aspergillide D is described using linear strategy. The salient features of this synthetic study include the Sharpless asymmetric kinetic resolution followed by regioselective ring-opening reaction of corresponding epoxide to establish the stereo centers and ring-closing metathesis (RCM) by Grubbs'-II catalyst for the construction of macrocyclic ring.     

Asymmetric approach towards the total synthesis of (+)-actinopyllic acid

This paper describes our efforts towards the asymmetric total synthesis of (+)-actinophyllic acid. Starting from the chiral oxazolidinone 9, an azocino [4,3-b]indolyl intermediate (5) possessing the A/B/C ring system and the C16 quaternary stereogenic center of actinophyllic acid has been synthesized. Key steps include a LHMDS-promoted condensation to establish the critical C2–C16 bond and a successive four-step transformation to assemble the eight-membered C-ring of the target molecule.     

Asymmetric synthesis of d-fagomine and its diastereoisomers

A divergent strategy for the asymmetric syntheses of d-fagomine and three of its diastereoisomers has been developed. The diastereoselective conjugate addition of an enantiopure lithium amide to an α,β-unsaturated ester was used as the key step to install the correct configuration required for the C(5)-stereogenic centre within the targets. In situ enolate oxidation generated the corresponding anti-α-hydroxy-β-amino ester, which possessed the correct configuration required for the C(4)-stereogenic centre within both d-fagomine and d-3-epi-fagomine. Subsequent epimerisation of this key anti-α-hydroxy-β-amino ester upon oxidation and diastereoselective reduction gave the corresponding syn-α-hydroxy-β-amino ester, which possessed the correct configuration required for the C(4)-stereogenic centre within both d-4-epi-fagomine and d-5-epi-fagomine. Elaboration of both α-hydroxy-β-amino esters upon reduction to the corresponding aldehydes followed by aldol reaction generated the requisite C(3)-stereogenic centres within the target compounds, then cyclisation and deprotection gave the enantiopure iminosugars in good overall yields, as single diastereoisomers (>99:1 dr).     

Asymmetric total synthesis of (+)-curcutetraol and (+)-sydonol

The asymmetric total syntheses of (+)-curcutetraol and (+)-sydonol, phenolic bisabolane-type sesquiterpenoids having chiral tertiary alcohol moiety in the o-position of a phenol, were achieved in high enantiomeric excesses (99% ee). The chiral tertiary benzylic alcohol moiety of these compounds was constructed by an asymmetric synthesis using an easily available chiral aminal, (−)-(2R,5S)-2-methoxycarbonyl-3-phenyl-1,3-diazabicyclo[3.3.0]octane. The absolute configurations of both (+)-curcutetraol and (+)-sydonol have been assumed to be S-configuration based on the stereochemical course of the well established asymmetric synthesis used in the syntheses.     

Asymmetric synthesis of (−)-tetrahydrolipstatin

Attempts toward the asymmetric synthesis of (−)-tetrahydrolipstatin are described. A palladium catalyzed Wacker-type reaction to convert an alkene to a ketone, highly diastereoselective reduction of a β-hydroxy ketone, selective oxidation of a diol, and modular synthesis are the key features of the successful approach.     

Asymmetric synthesis of (+)-L-733,060

A concise, stereocontrolled synthesis of (+)-L-733,060 was achieved. Key features involve diastereoselective oxazoline formation catalyzed by palladium(0) and intramolecular cyclization by catalytic hydrogenation of an oxazoline.     

Asymmetric synthesis of SMS-Phos series’ precursor and a naphthalene analogue

An efficient and high-yielding (up to 57% overall yield) asymmetric route to enantiopure P-stereogenic 1,2-bis[(o-hydroxyaryl)(phenyl)phosphino-P-borane]ethanes wherein aryl = phenyl and naphthyl, is presented. The occurring P-stereomutation is confirmed through X-ray crystal structure analysis of key intermediates.     

Asymmetric synthesis of a potent azepanone-based inhibitor of the cysteine protease cathepsin K

In this account we detail the asymmetric synthesis of 1, a potent azepanone-based inhibitor of cathepsin K (K_i = 0.16 nM), which has been shown to inhibit the production of biomarkers of bone resorption in monkeys. The key steps in the synthesis sequence were the utility of the Evans aldol reaction coupled with the ring closing olefin metatheses to assemble the azepanone core contained within 1.