Syntheses of l-glucosamine donors for 1,2-trans-glycosylation reactions
摘要:
Two new L-glucosarnine donors, that is pent-4-enyl 3,4,6-tri-O-acetyl-2-allyloxycarbonylamino-2-deoxy-beta-L-glucopyranoside 16 and ethyl 3,4,6-tri-O-acetyl-2-allyloxycarbonylamino-2-deoxy-l-thio-beta-L-glucopyranoside 21 were prepared in 12 steps from L-arabinose. The reaction pathway uses 3,4,6-tri-O-acetyl-L-glucal 5, and then 3,4,6-tri-O-acetyl-2-deoxy-2-iodO-alpha-L-mannopyranosyl azide 8 as intermediates. The latter, together with donors 16 and 21, were used for preparing L-glucosamine neoglycolipids. (c) 2007 Elsevier Ltd. All rights reserved.
Synthesis and interfacial behavior of three homologous glycero neoglycolipids with various chain lengths
摘要:
Three neoglycolipids la-e derived from glycerol were synthezised and their molecular arrangements were studied at the air/water interface through Langmuir-Blodgett technique. The common structural features of these neoglycolipids are: a triethyleneglycol spacer at C-2 of glycerol, a GlcNAc hydrophilic head group at the end of the spacer, two saturated aliphatic chains at C-l and C-3 of glycerol, linked by ether bonds. Compounds la-e differ only by the length of their lipid moieties. By increasing the hydrocarbon chain length from C-11 to C-16, a densely packed state was reached in the monolayer. The compression isotherms displayed an expanded state during the whole compression for compounds la and Ic bearing two C-11 or one C-11 and one C-16 chains. Compound 1b bearing two C-16 chains displayed a quite different interfacial behavior. The transfer of these monolayers onto a solid substrate can be obtained only with a trigger molecule, a phosphatidic acid. (C) 1997 Elsevier Science Ireland Ltd.