Synthesis of the AB disaccharide

Our development of the tartrate ester modified allylboronates c.h suggested to us that many of these problems could be avoided by using the reaction of a chiral aldehyde and a chiral allylboronate as a means of establishing the stereochemistry of the sugar backbone. This strategy has been used in our synthesis of the AB disaccharide unit of olivomycin A (Figures 16, 17).3 ... 

A series of avermectin analogues have been prepared with spacer arms between the disaccharide and the aglycone. Some of the products showed considerable bioactivity. This disaccharide (107) and epimers at C-4 and C-3 were made for use in the synthesis of mithramycin and related antitumour agents, and the AB disaccharide of olivomycin A, 2,6-dideoxy-3-0-(2,6-dideo qr-tf-D-fyxo-hexosyl)-Z)-it)ao-hexose was produced using the highly selective synthesis of 2-deoxyhexoses from 4-deoxy-2,3-0-isopropylidene-D-threose (Chapter 12). ... 

In the block synthesis, the target oligosaccharide is assembled from a few smaller ohgosaccharides. As shown in Scheme 5.3, for the synthesis of an ABCD oligosaccharide the AB (17) and CD (8) disaccharide blocks are synthesized in parallel and coupled after a single deprotection step (8 9) to afford the protected tetrasaccharide (14). 

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