Tetrasaccharides, methyl derivatives

Methyl Ethers. - A number of mono-O-methyl derivatives of a tetrasaccharide have been prepared and their relative binding characteristics to a lectin studied. 3-0-Methyl-6-deoxy-L-talose has been prepared and glycosyl-bonded to a tetrapeptide, and the methylation of some nucleoside derivatives is mentioned in Chapter 20. 

The methyl 3 -0-allyl-P-lactoside (97) prepared by Veyrieres by the allylation of the dibutylstannylene derivative in the presence of tetrabutylammonium bromide [102] was converted into the per-p-bromobenzyl ether and deallylated to give (306). This was condensed "[106] with the chloride (282) in the presence of silver triflate to give a tetrasaccharide in 68 % yield. This was far superior to the condensation of the oxazoline (294) with (306) which gave a very low yield (9%) of tetrasaccharide. Depro-... 

Ogawa and co-workers [97] have synthesised the complete glycosphingolipid (361) containing the terminal tetrasaccharide (356) of the Leb antigen attached to lactosyl ceramide. The lactose derivative (95), prepared by the action of trimethylamine — borane and aluminium chloride [99] on the benzylidene derivative (94), was condensed with the thioglucoside (362) in the presence of methyl triflate and molecular sieve to give the trisaccharide (363). This was deacetylated and the product (364) condensed... 

The derivatives 3-<9-methyl-D-olivose (D-oleandrose, 3-<9-methyl-2,6-dideoxy-D-arabino-hexose), and 3-0-methyl-D-oliose (3-<9-methyl-2,6-dideoxy-D-/yvo-hexose) are components of steroidal glycosides obtained from Cynanchum othophyllum Schneid, a traditional Chinese medicine.148 A derivative 4-O-me-thyl-D-olivose has been identified as the terminal sugar of the tetrasaccharide moiety in the phenolic glycolipid of Mycobacterium kansasii.149... 

Derivative 13 was deprotected to give the triheptoside backbone of the Salmonella core [19], but the protecting pattern in 13 was also chosen to allow further synthesis of core structures. Thus, debenzylation of 13 to give the 2, 3, 4 -triol, followed by the orthoester protocol, once more gave a 3 -OH acceptor (14), which was reacted with methyl 2,3,4,6-tetra-O-benzyl-l-thio- -o-gluco-pyranoside and DMTST to give the tetrasaccharide 15 (Scheme 7). 

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