Total synthesis of allosamidin

For the synthesis of allosamidin, the glycosylation of 24 with oxazoline 60, obtained by treatment of 2-acetamido-2-deoxy-p-D-glycopyranose-l,3,4,6-tetraacetate with BF3 OEt2, using triflic acid as catalyst gave the p-anomer of the pseudodisaccharide 61 (50%), which underwent deprotection to produce 62. 

Selective deacetylation of 63 provided 64 in 95% yield. Protection of 64 with TB-SCl followed by deacetylation with methanolic ammonia gave 65. The resulting carbamate 66 (82%) was desilylated with aqueous HF to produce 67 (94%). This was subsequently converted to 24, via 68, whose selective benzylation gave 69 as a suitable glycosyl acceptor. Finally, hydrogenolysis of 24 provided (-)-allosamizoline (8). 

Coupling of 95 with 24 gave the 3-linked products 96 and 97 in the ratio 5 1 in 68% yield. Dephthaloylation of componnds 96 and 97 was effected by nse of aqneons methylamine. The resnlting mixture of diamines was acetylated and snbseqnently deprotected to give allosamidin 2 and its isomeric product 98. 

The donor 113 was coupled with the acceptor 69 to give the fully protected allosamidin derivative 114 (40%). Finally, removal of all protecting groups from 114 furnished (—)-allosamidin (2). 

Pariser, E.R. Chitin Source Book A Guide to the Research Literature, Wiley New York, 1989. 

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Many syntheses of allosamizoline and its analogues from noncarbohydrate have been reported. "" Carbohydrates have been also used for the synthesis of allosamizoline, which upon suitable protection to be a glycosyl acceptor that can be coupled with the required oligosaccharide donor would led to the total synthesis of allosamidin. 

Griffith DA, Danishefsky SJ. The total synthesis of aUosamidin. Expansions of the methodology of aza-glycosidation pursuant to the total synthesis of allosamidin. A surprising enantiotopic sense for a lipase-induced deacetylation. Journal of the American Chemical Society 118, 9526, 1996. 

A total synthesis of allosamidin is mentioned in Chapter 3. Full details of the synthesis of allosamizoline, the aglycone of allosamidin, have been reported. Studies of allosamidin biosynthesis using labelled D-glucose and D-glucosamine indicate that the latter sugar is the precursor to each N-acetyl-o-allosamine and to the allosamizoline component. ... 

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