Oligosaccharide Analogues of Polysaccharides Cross-Coupling of Partially Protected Dialkynyl Monosaccharides

摘要

The dependency of the cross-coupling of orthogonally C-protected dialkynyl monosaccharides on the nature of the coupling partners has been studies.The required dialkyne 5 was synthesized from levoglucosan in six steps and 39% overall yield and transformed into 7,10,12,13,and 14 by orthogonal C-deprotection and bromination (Scheme 1).Optimization of the conditions of their cross-coupling to 16 showed that yields were higher for the coupling of the propargylic bromoalkyne 10 than for the homopropargylic bromoalkyne 14 (Scheme 2).Deprotection of 16 gave the nano-crystalline dimer 20.To obtain more highly crystalline products,the monomers 7 and 13 were coupled with 1-iodo-4-nitrobenzene to the arylated monomers 21 and 24(Scheme 3).The 4-NO_2C_6H_4 substituent lowered the yield of the dimerizations to the mono- and diarylated dimers 26-28 (Scheme 4)but had no effect on crystallinity.