Synthesis of phosphatidylinositol mannosides (PIMs)

Two strategies towards the synthesis of phosphatidylinositol mannosides (PIMs) were elaborated which permit selective access to the O-1-, O-2-, and the O-6 position of the myo-inositol residue. Starting materials are 1,2:5,6- and 1,2:4,5-di-O-cyclohexylidene-DL-myo-inositol, respectively. In the latter case, the required assignment to the D- or L-series is based on the transformation of one enantiomer into known (-)-liriodentritol. The efficiency and potential versatility of the two approaches is exemplified in the synthesis of PIMs (D)-1a and its pseudoenantiomer (L)-1b, both having myristoyl residues as part of the phosphatidyl moiety.     

Two approaches to the synthesis of 3-beta-D-glucopyranosyl-D-glucitol

Glycosidation of 1,2:5,6-di-O-isopropylidene-D-glucose with tetra-O-acetyl-glucosyl bromide in 1:1 benzene-MeNO2 afforded approximately equal amounts of the 3-O-beta-D-glycoside and the rearranged 6-O-beta-D-glycoside, while in MeCN only the latter was formed. When tetra-O-acetyl-beta-thiophenylglucoside was used as donor in CH2Cl2 in the presence of NIS/TfOH as activator, the 6-O-beta-D-glycoside and a 3-O-orthoester were formed in a 1:2 ratio at -20 degrees C, while at 20 degrees C only the former could be isolated. Glycosidation of 1-O-benzoyl-2,4-O-benzylidene-5,6-O-isopropylidene-d-glucitol with tetra-O-acetyl-glucosyl bromide in MeCN in the presence of Hg(CN)2 afforded the corresponding 3-O-alpha- and 3-O-beta-glycopyranoside in a 1:4 ratio in MeCN and 1:5 in 1:1 benzene-MeNO2, respectively. When Hg(CN)2/HgBr2 was used as promoter, the corresponding orthoester was also formed. When tetra-O-acetyl-beta-thiophenylglucoside was used as donor, the 3-O-beta-anomer and the orthoester were obtained predominantly in a 3:2 ratio together with traces of the 3-O-alpha-glycoside. Both beta-glycosides could be smoothly converted into 3-beta-D-glucopyranosyl-D-glucitol.