We describe here an application of the practical, simple, and reliable approach for the determination of the absolute configuration of sterically demanding tert/tert vic-diols. According to this method, it is only necessary to mix dimolybdenum tetraacteate and a chiral diol in DMSO and record the CD spectra in the 250-650 nm spectral range. From the sign of the CD bands occurring at around 310, 350, and 400 nm, it is possible to establish the chirality of the diol unit expressed by the sign of the O-C-C-O torsion angle. Because the preferred conformation of the diol in the formed complex is known, we are able to determine the absolute configuration of the carbon atoms in the diol subunit even in flexible tert/tert vic-diols.
Saponin OSW-1 (5e-G2; 3 beta,16 beta,17 alpha-trihydroxycholest-5-en-22-one 16-O-{O-[2-O-(4-methoxybenzoyl)-beta-D-xylopyranosyl]-(1-->3)-2-O-acetyl-alpha-arabinopyranoside}) analogues: with modified side chain (5a/d-G2), 22-deoxo-23,24,25,26,27-pentanor- (14), 22-deoxo-23-oxa- (17), glycosylated with various monosaccharides (5e-G4/G6/G8), and OSW-1 structural isomer (10) were obtained. The analogues were synthesized using a previously published method for the synthesis of OSW-1. The structures of analogues were fully confirmed by spectroscopic methods, and the S-chirality at C-22 of the structural isomer was established by conformational analysis combined with the NMR spectrometry. The cytotoxicity of the analogues toward several types of malignant tumor cells was examined and compared with that of OSW-1. The results suggest that modification of the steroidal aglycone may lead to compounds with high cytotoxicity.
A practical
synthesis of menaquinone-7 (MK-7, vitamin K2) in the all-trans form was designed. Stereoselective
synthesis of MK-7 was achieved through a “1 + 6” convergent
strategy by condensation of two building blocks, menadione monoprenyl
derivative (fragment “1”) with hexaprenyl bromide (fragment
“6”, 82%). Pd-catalyzed desulfonation with LiEt3BH (78%) was followed by oxidation of the hydroquinone moiety
using ammonium cerium(IV) nitrate (72%). The major challenge in our
methodology was the preparation of all-trans hexaprenyl
bromide by coupling of two triprenyl units derived from trans,trans-farnesol. Manufacturing on a pilot scale was accomplished through
our approach. The scalable method was designed especially for a large,
kilogram-scale production from easily available intermediates. Furthermore,
the proposed methodology avoids many chromatographic purifications
and allows for a relatively cost-effective manufacturing. Moreover,
our synthesis yielded high-purity (99.9%) final product MK-7, which
can be used as a dietary supplement as well as an active pharmaceutical
ingredient.
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