Convergent Synthesis of the Nonreducing Hexasaccharide Fragment and the Dodecasaccharide Scaffold of Marine Lipopolysaccharide Axinelloside A

A convergent synthesis of properly protected dodecasaccharide backbone of axinelloside A was accomplished by virtue of an Au(I)-catalyzed [6+6] glycosylation. The 1,2-cis configuration of the glycosidic bonds was well controlled by judicious choice of protecting groups as well as promotion conditions.

Abstract

A convergent synthesis of the dodecasaccharide scaffold of axinelloside A was achieved through Au(I)-catalyzed [6+6] glycosylation. The initially devised [3+1+2] assembly of the nonreducing hexasaccharide fragment was low-yielding, whereas a convergent [3+3] glycosylation under Au(I) catalysis was proven feasible, allowing for a semi-gram scale preparation of the wanted hexasaccharide. The requisite 1,2-cis glycosidic bonds were forged in a highly stereoselective fashion by virtue of remote acetyl group participation, and judicious manipulation of protecting groups. The synthetic dodecasaccharide has been properly protected for the downstream elaboration toward its natural form.

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