Systematic syntheses of the isoglobo-series gangliosides, α-sialyl-(2 → 3)- and -(2 → 6)-isoglobopentaosyl ceramides (21 and 24, V 3Neu5AciGb 5Cer and V 6Neu5AciGb 5Cer) are described. 2-(Trimethylsilyl)ethyl 2-O- benzyl-4,6-O- benzylidene-α- d-galactopyranosyl -(1 → 3)2,4,6- tri-O- benzyl-β- d-galactopyranosyl -(1 → 4)-2,3,6- tri-O- benzyl-β- d-glucopyranoside (4), the core structure of the isoglobo-series gangliosides was prepared by the glycosylation of 2-(trimethylsilyl)ethyl 2,4,6- tri-O- benzyl-(1 → 4)-2,3,6- tri-O- benzyl-β- d-glucopyranoside (2) with methyl 3-O- acetyl-2-O- benzyl-4,6-O- benzylidene-1-thio-β- d-galactopyranoside (1), and subsequent O-deacetylation. Coupling of 4 and methyl 3-O- acetyl-4,6-O- benzylidene-2-deoxy-2-phthalimido-1-thio-β- d-galactopyranoside gave an isoglobotetraoside derivative 6, from which the phthaloyl and O-acetyl groups were removed. N-Acetylation then gave a tetrasaccharide acceptor 7. Dimethyl(methylthio)sulfonium triflate-promoted coupling of 7 with methyl (methyl 5- acetamido-4,7,8,9-tetra-O- acetyl-3,5-dideoxy- d -glycero- α- d -galacto)-(2 → 3)-2,4,6- tri-O- benzoyl-1-thio-β- d-galactopyranoside or - (2 → 6)-2,4- di-O- benzoyl-3-O- benzyl-1-thio-β- d-galactopyranoside gave the pentasaccharide derivative 9 and 14 in good yields. Compounds 9 and 14 were converted into the corresponding α-trichloroimidates 12 and 17 which, on coupling with (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (18), gave the β-glycoside 19 and 22, respectively. Finally, 19 and 22 were transformed, via selective reduction of azide group, condensation with octadecanoic acid, O-deacylation, and hydrolysis of the methyl ester group into 21 and 24, respectively.