Synthesis, Structural Elucidation, And Biochemical Analysis of Immunoactive Glucuronosyl Diacylglycerides of Mycobacteria and Corynebacteria

Abstract

Glucuronosyl diacylglycerides (GlcAGroAc2) are functionally important glycolipids and membrane anchors for cell wall lipoglycans in the Corynebacteria. Here we describe the complete synthesis of distinct acyl-isoforms of GlcAGroAc2 bearing both acylation patterns of (R)-tuberculostearic acid (C19:0) and palmitic acid (C16:0) and their mass spectral characterization. Collision-induced fragmentation mass spectrometry identified characteristic fragment ions that were used to develop "rules" allowing the assignment of the acylation pattern as C19:0 (sn-1), C16:0 (sn-2) in the natural product from Mycobacterium smegmatis, and the structural assignment of related C18:1 (sn-1), C16:0 (sn-2) GlcAGroAc2 glycolipids from M. smegmatis and Corynebacterium glutamicum. A synthetic hydrophobic octyl glucuronoside was used to characterize the GDP-mannose-dependent mannosyltransferase MgtA from C. glutamicum that extends GlcAGroAc2. This enzyme is an Mg(2+)/Mn(2+)-dependent metalloenzyme that undergoes dramatic activation upon reduction with dithiothreitol.

Modulating glycosylation with exogenous nucleophiles: an overview

“…75 The reaction required 6 days for completion and the glucoside intermediate 92 was obtained in high selectivity. Upon post-glycosylation modification, the glucoside 92 was converted to the target glucuronosyl diacylglyceride 93.…”

COMU: scope and limitations of the latest innovation in peptide acyl transfer reagents

“…Successful Weinreb amidation of several Boc-amino acids (63-97% yield) and aliphatic acids has been recently achieved [15,33]. In addition, the use of COMU (16) in bioconjugation, anilide, and PNA-based construct formation has been described in numerous occasions [27,[34][35][36][37][38][39].…”

Total synthesis and mass spectrometric analysis of a Mycobacterium tuberculosis phosphatidylglycerol featuring a two-step synthesis of (R)-tuberculostearic acid

“…Numerous syntheses of R-TBSA have been reported, using chiral pool sources, 17,19,20 chiral auxiliaries, 21 catalytic enantioselective induction, 10,18 and resolution methods [14][15][16] (Table 1). The most efficient synthesis reported to date is that of Roberts and Baird who prepared TBSA in four steps from (S)-citronellyl bromide, in a route involving stepwise elongations using copper(I)-catalyzed cross-coupling and Wittig extension.…”

“…Hydrogenolysis Scheme 1 Two-step synthesis of (R)-tuberculostearic acid. Chiral pool/5 steps Hung, 2015 20 Chiral auxiliary/ 7 steps Williams, 2013 21 Chiral pool/4 steps Baird, 2006 22 of the benzyl ether afforded the diacylglycerols 7a-c, which were used immediately without purification in the next step. Assembly of the PG structure relied upon the use of a phosphordiamidite linchpin, benzyl bis(N,N-diisopropyl)phosphordiamidite (Scheme 3).…”