Synthesis of Carba- and C-Fucopyranosides and Their Evaluation as α-Fucosidase Inhibitors − Analysis of an Unusual Conformation Adopted by an Amino-C-fucopyranoside
摘要:
Several carba- and C-fucopyranosides bearing a variety of substituents at their pseudoanomeric positions have been synthesized and tested as inhibitors of bovine kidney a-fucosidase. From the IC50 values, some conclusions about the structure-activity relationship could be drawn, The presence of a hydroxyl group close to the pseudoanomeric position, or the presence of an aromatic ring as substituent, were beneficial for inhibitory activity. A 1-(R)-amino-phenylmethyl C-fucopyranoside, the activity of which increased 40 times when the pH was changed from 5.0 to 7.0, adopted a C-4(1) conformation, in contrast to the C-1(4) form normally adopted by natural fucopyranosides. The conformation of this compound was analyzed in comparison with that of the 1-(S)-configured epimer, using NMR spectroscopy and molecular modeling.
alpha-L-fuco-, alpha-D-gluco-, beta-D-gluco-, and alpha-D-mannopyranose have been synthesized from the corresponding glycosyl phenyl sulfoxide through phenylsulfinyl-lithium exchange, to generate an anomeric carbanion, and subsequent reaction with a carbon electrophile. The reactions were stereospecific and proceeded with retention of the configuration at the anomeric center. Improved yields of C-glycosides
Phenylsulfinyl-lithium exchange on glycosyl phenylsulfoxides leads to configurationally stable anomeric carbanions which can react stereoselectively with electrophiles. Thus, the reaction of 3,4-O-isopropylidene-α-l-fucopyranosyl phenylsulfoxide with tBuLi followed by treatment with isobutyraldehyde led to the α-configured C-glycoside; the β-anomer furnished the corresponding β-C-glycoside.