De Novo Synthesis of Oligosaccharides

项目总结

Project Summary The overall objective of this proposal renewal is to continue our development of an efficient and general strategy for the asymmetric synthesis of oligosaccharides (X = O) and to expand it to the synthesis of analogous oligo-cyclitols (X = CH2, Scheme 1). The method we propose has the potential to revolutionize the way oligosaccharides are synthesized. Our method revolves around the use of a highly stereoselective palladium catalyzed glycosylation (X = O: 2.1¿/2.4¿ to 2.2 ¿/2.5¿) and cyclitolization (X = CH2; Scheme 1). There has been an astounding amount of research directed toward the synthesis of oligosaccharides; however, when it comes to unnatural oligosaccharides, the current state of the art is lacking. This deficiency is undoubtedly due to the limited number of carbohydrate starting materials (glucose, mannose, and galactose). A complementary approach would be to start with a significantly simplified structure and to sequentially increase its stereochemical and functional complexity to a range of structures (eg., 1.5/1.6 to 1.1-1.3; Scheme 1). The underlying hypothesis that guides our synthetic approach is the belief that there are many carbohydrate analogs, which remain undiscovered because of synthetic limitations. Thus, we believe a methodology that allows for the facile incorporation of simple sugars (i.e. under-functionalized) into oligosaccharide motifs will drastically enable the discovery of new structures with a wide range of functions.