Synthesis of blockwise alkylated (1→4) linked trisaccharides as surfactants: influence of configuration of anomeric position on their surface activities

New carbohydrate-based surfactants consisting of hydrophilic cellobiosyl and hydrophobic glucosyl residues, methyl β-d-glucopyranosyl-(1→4)-α-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-α-d-glucopyranoside 1 (GβGαMα, G: glucopyranosyl residue, α and β: α-(1→4)- and β-(1→4) glycosidic bonds, M: methyl group), 2 (G_βG_βM_α), 3 (G_βG_αM_β), 4 (G_βG_βM_β), 5 (G_βG_αE_α, E: ethyl group), 6 (G_βG_βE_α), 7 (G_βG_αE_β), 8 (G_βG_βE_β) and eight α-and β-glycoside mixtures (a mixture of 1 and 2: 1/2 = 62/38 (9), 32/68 (10); a mixture of 3 and 4: 3/4 = 69/31 (11), 32/68 (12); a mixture of 5 and 6: 5/6 = 62/38 (13), 33/67 (14); a mixture of 7 and 8: 7/8 = 59/41 (15), 29/71 (16)) were synthesized via combined methods consisting of acid-catalyzed alcoholysis of cellulose ethers and glycosylation of phenyl thio-cellobioside derivatives. Their surface activities in aqueous solution depended on their chemical structures: α- or β-(1→4) linkage between hydrophilic cellobiosyl and hydrophobic glucosyl blocks, methyl or ethyl groups of hydrophobic glucosyl block, and α- or β-linked ether group at the C-1 of hydrophobic glucosyl block. The mixing effect of α- and β-glycosides on surface activities was also investigated. As a result, ethyl β-d-glucopyranosyl-(1→4)-α-d-glucopyranosyl-(1→4)-2,3,6-tri-O-ethyl-β-d-glucopyranoside 7 (G_βG_αE_β) had the highest surface activity, and its critical micellar concentration (CMC) and γ_CMC (surface tension at CMC) values of compound 7 were 0.5 mM (ca. 0.03 wt %) and 34.5 mN/m, respectively. The surface tensions of α- and β-glycoside mixtures except for compounds 9 and 10 were almost equal to those of pure compounds. The syntheses of the mixtures of α- and β-glycosides without purification process are easier than those of pure compounds. Thus, the mixtures should be more practical compounds for industrial use as a surfactant.