The glycosylation of 1,2‐trans‐diequatorial diols derived from tetrabenzoylated and tetrabenzylated D‐ and L‐chiro‐inositol with several glycosyl donors has been investigated. An unprecedented dependence of the regioselectivity on the absolute configuration of the acceptor has been found. However this trend is also modulated by the nature of the protecting groups on both the donor and acceptor, with benzoylated acceptors affording higher levels of regioselectivity. Most of the results have been rationalized by DFT calculations which indicate that stereoelectronic factors and hydrogen bonding between the donor and acceptor govern their relative orientation and determine the regiochemical outcome of the process. These studies also highlight the role of the acyl group adjacent to the OH to be glycosylated in facilitating the glycosylation reaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

New and highly effective procedures for the preparation of d-chiro-inositol derivatives, essentially based on selective protection of the vicinal diequatorial diol systems present in this molecule, are reported. This selective protection affords C 2 -symmetric diaxial diols such as 4 and 5, glycosylation of

We have developed an efficient synthetic strategy to HexNH2‐α(1⇄3)‐L‐chiro‐inositol (XII−XIII) and HexNH2‐α(1⇄2)‐D‐chiro‐inositol (XIV−XV) based on the regio and stereoselective glycosylation of tetrabenzoyl‐L‐chiro‐inositol 2 and tetrabenzyl‐D‐chiro‐inositol 14. Compounds XII−XV may constitute the central structural motifs of inositolphosphoglycans, which have been proposed as putative insulin mediators, and their syntheses have been designed on the basis of biosynthetic considerations. The syntheses of XII−XIII and XIV−XV involve the selective monoglycosylation of an L‐chiro inositol diequatorial diol system (2) and a D‐chiro inositol axial/equatorial diol system (14), respectively. To establish the experimental conditions to achieve the best reactivity−selectivity balance, the glycosylation reactions were studied using D‐gluco‐ and D‐galacto‐configured 2‐azido‐2‐deoxytrichloacetimidate glycosyl donors with different reactivities. The results obtained provide a practical synthetic route and new reactivity−selectivity data. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The nature of chiro-inositol-containing inositolphosphoglycans (IPGs), reported to be putative insulin mediators, was studied by examination of the substrate specificities of the phosphatidylinositol-specific phospholipase C (PI-PLC) and the glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) by using a series of synthetic D- and L-chiro-glycosylphosphoinositides. 3-O-alpha-D-Glucosaminyl- (3) and -galactosaminyl-2-phosphatidyl-L-chiro-inositol (4), which show the maximum stereochemical similarity to the 6-O-alpha-D-glucosaminylphosphatidylinositol pseudodisaccharide motifs of GPI anchors, were synthesized and asymmetrically incorporated into phospholipid bilayers in the form of large unilamellar vesicles (LUVs). Similarly, 2-O-alpha-D-glucosaminyl- (5) and -galactosaminyl-1-phosphatidyl-D-chiro-inositol (6), which differ from the corresponding pseudodisaccharide motif of the GPI anchors only in the axial orientation of the phosphatidyl moiety, were also synthesized and asymmetrically inserted into LUVs. The cleavage of these synthetic molecules in the liposomal constructs by PI-PLC from Bacillus cereus and by GPI-PLD from bovine serum was studied with the use of 6-O-alpha-D-glucosaminylphosphatidylinositol (7) and the conserved GPI anchor structure (8) as positive controls. Although PI-PLC cleaved 3 and 4 with about the same efficiency as 7 and 8, this enzyme did not accept 5 or 6. GPI-PLD accepted both the L-chiro- (3 and 4) and the D-chiro- (5 and 6) glycosylinositolphosphoinositides. Therefore, IPGs containing L-chiro-inositol only are expected to be released from chiro-inositol-containing GPIs if the cleavage is effected by a PI-PLC, whereas GPI-PLD cleavage could result in both L-chiro- and D-chiro-inositol-containing IPGs.

No abstract

Synthesis of New Hexosaminyl D-and L-chiro-Inositols Related to Putative Insulin Mediators. -The title compounds [cf. (IV) and (V)] are prepared via regio-and stereoselective glycosylation. -(CID, M. B.; BONILLA, J. B.; ALFONSO, F.; MARTIN-LOMAS*, M.; Eur.

No abstract

No abstract