The rational design and synthesis of a biochemical probe of natural (+)-macrosphelide A, a potent cell–cell adhesion inhibitor, was completed to aid in the identification of its biological target. The key features of the synthesis include: (1) an efficient synthesis of the macrosphelide core structure using Yamaguchi–Hirao alkynylation, (2) a cross metathesis to connect a linker unit to the allyl-macrosphelide and (3) coupling of the linker-bound macrosphelide A with a chemical biotin tag.
Diastereoselectivity in the boron aldol reaction of α-alkoxy and α,β-bis-alkoxy methyl ketones
作者:Alessandra A. G. Fernandes、Ives A. Leonarczyk、Marco A. B. Ferreira、Luiz Carlos Dias
DOI:10.1039/c9ob00358d
日期:——
In this work, using DFT calculations, we investigated the 1,4 and 1,5 asymmetric induction in boron enolate aldol reactions of α-alkoxy and α,β-bisalkoxy methylketones. We evaluated the steric influence of alkyl substituents at the α position and the stereoelectronic influence of the oxygen protecting groups at the α and β positions. Theoretical calculations revealed the origins of the 1,4 asymmetric
For an improved synthesis of the recently described expanded octamethoxycubane with a central C56 core, formally obtained by inserting buta-1,3-diynediyl moieties into all C(sp3)–C(sp3) bonds of octamethoxycubane, the preparation of the optically pure methyl ether of a differentially silyl-protected trispropargylic alcohol was required. The key step of the preparation involved a diastereoselective addition of a lithium acetylide to an optically active alkynyl ketone under Cram chelation control.
Highly concise syntheses of (+)-macrosphelides A and B were accomplished in this study. The key feature of our synthetic route involved the direct three-carbon homologation of the readily available Weinreb amide 6 by the addition of a trans-vinylogous ester anion equivalent and facile construction of the 16-membered macrolide skeleton of macrosphelides via an intramolecular nitrile oxide−olefin cycloaddition
An enantioselective synthesis of the C<sub>24</sub>–C<sub>40</sub> fragment of (−)-pulvomycin
作者:Sandra Börding、Thorsten Bach
DOI:10.1039/c4cc01338g
日期:——
The C24–C40 fragment of (−)-pulvomycin was prepared in enantiomerically pure form using a concise synthesis method (15 linear steps from d-fucose, 6.8% overall yield) featuring a diastereoselective addition to an aldehyde, a β-selective glycosylation and a Stille cross-coupling as the key steps.