An easy α-glycosylation methodology for the synthesis and stereochemistry of mycoplasma α-glycolipid antigens

Abstract

Summary Mycoplasma fermentans possesses unique α-glycolipid antigens (GGPL-I and GGPL-III) at the cytoplasm membrane, which carry a phosphocholine group at the sugar primary (6-OH) position. This paper describes a practical synthetic pathway to a GGPL-I homologue (C16:0) and its diastereomer, in which our one-pot α-glycosylation method was effectively applied. The synthetic GGPL-I isomers were characterized with 1H NMR spectroscopy to determine the equilibrium among the three conformers (gg, gt, tg) at the acyclic glycerol moiety. The natural GGPL-I isomer was found to prefer gt (54%) and gg (39%) conformers around the lipid tail, while adopting all of the three conformers with equal probability around the sugar position. This property was very close to what we have observed with respect to the conformation of phosphatidylcholine (DPPC), suggesting that the Mycoplasma glycolipids GGPLs may constitute the cytoplasm fluid membrane together with ubiquitous phospholipids, without inducing stereochemical stress.

Remarkable functions of sn-3 hydroxy and phosphocholine groups in 1,2-diacyl-sn-glycerolipids to induce clockwise (+)-helicity around the 1,2-diacyl moiety: Evidence from conformation analysis by 1H NMR spectroscopy

“…From X-ray crystallography data, a common structure in which the 1,2-diacyl chains are aligned in parallel is observed, which adopts either the gt(+) or gg(−) conformer [ 7 , 10 , 12 ]. An analogous conformation has been reportedly observed among α-glycosyl 1,2-diacyl- sn -glycerols in the solution state [ 16 ]. Probably, the two gauche conformers, namely gt(+) and gg(−), are stabilized in a manner so as to permit stacking interactions between the 1,2-diacyl chains.…”

“…In fact, the 1 H NMR Karplus analysis indicates that the helical disparity of 4 increases above 30% ( Table 3 , entries 1 and 2); the disparity is greater than that observed thus far in previously reported studies [ 16 – 18 ]. When previously reported 1 H NMR data for 4 are examined [ 8 , 10 , 31 ], the strong (+)-chirality is independent of the solvents used ( Table 3 , entries 1–4).…”

“…Probably, the range between B2 and C1 sections in the diagram covers the conformational properties of most 1,2-diacyl- sn -glyceols in the solution state. The conformational properties in this region can be characterized by the relation of gt(+) > gg(−) > tg (%), which has been commonly observed in our preceding studies [ 16 – 18 ].…”

“…The helical conformational properties of these α-glycolipids are determined by Eq. 2 applying the 1 H NMR data reported in a preceding paper [ 16 ]. The results of the 1 H NMR analyses are compared with those calculated by Eq.…”

“… a Abbreviations: α-D- or α-L-Glc = α-D- or α-L-glucopyranoside, b1 H NMR data in our preceding study [ 16 ] are analyzed with Eq. 2 ; c calculated values (%) from Eq.…”