Selenoglycosides. 3. Synthesis of Phenyl 2-(N-Acetylamino)- and 2-Azido-2-deoxy-1-seleno-α-D-glycopyranosides via Azido-phenylselenylation of Diversely Protected Glycals

Article abstract of DOI:10.1021/jo00105a051

Two methods are described for the preparation of diversely protected phenyl 2-azido-2-deoxy-α-D-selenoglycopyranosides from protected glycals.In the first one (method A), a peracetylated glycal is treated with sodium azide and diphenyl diselenide in the presence of (diacetoxyiodo)benzene in dichloromethane at rt.With 3,4,6-tri-O-acetyl-1,5-anhydro-2-deoxy-D-arabino-hex-1-enitol (tri-O-acetyl-D-glucal) an inseparable mixture of phenyl 2-azido-2-deoxy-α-gluco- and -α-manno-selenoglycosides is obtained (91percent yield).With 3,4,6-tri-O-acetyl-1,5-anhydro-2-deoxy-D-lyxo-hex-1-enitol (tri-O-acetyl-D-galactal) only the α-galacto isomer is obtained (92percent).Method A is not compatible with benzyl groups.In method B, a perbenzylated glycal is reacted with trimethylsilyl azide and tetra-n-butylammonium fluoride in the presence of N-phenylselenophthalimide.From protected D-glucal a gluco/manno mixture is obtained, whereas only the galacto isomer is formed from protected D-galactal (75percent yield).The compatibility of method B with a variety of protecting groups is exemplified with 6-O-acetyl, 6-O-benzyl, and 6-O-(tert-butyldimethylsilyl)-3,4-O-isopropylidene-1,5-anhydro-2-deoxy-D-lyxo-hex-1-enitol.The same diastereocontrol is observed, and the α-D-galacto isomer is obtained (60-70percent yield).Reduction of the azido group of these selenoglycosides with 1,3-propanedithiol in the presence of triethylamine and acetylation affords the corresponding phenyl 2-(N-acetylamino)-2-deoxy-α-D-selenoglycopyranosides in good yield.