TCP-PROTECTED AND PHTHALIMIDE-PROTECTED N-PENTENYL GLUCOSAMINIDE PRECURSORS FOR THE SYNTHESIS OF NODULATION FACTORS AS ILLUSTRATED BY THE TOTAL SYNTHESIS OF NODRF-III (C18 1, MEFUC)/

TCP- and phthalimide-protected n-pentenyl glucosaminide (NPG) precurso rs have been utilized in a convergent stereocontrolled synthesis of th e nodulation factor NodRf-III (C18:1, MeFuc) produced by Rhizobium fre dii USDA257, 2. Nodulation factors are lipooligosaccharides that are s ecreted by bacteria which trigger the early steps in the formation of root nodules in leguminous plants. This symbiotic relationship between plant and bacteria plays a major role in the global nitrogen cycle. K ey to our synthetic approach was the use of the TCP (tetrachlorophthal oyl) group to provide for N-differentiation of the linear glucosamine backbone and the use of FeCl3 for the removal of benzyl protecting gro ups from the tetrasaccharide. The saccharide skeleton was assembled vi a the NPG-based coupling of a linear beta(1-->4) glucosamine disacchar ide to a 6-O-fucosylated glucosamine acceptor. Significant yield enhan cements for NPG couplings were observed at lower temperatures. Subsequ ent exchange of benzyl to tert-butyldimethylsilyl protecting groups vi a FeCl3 mediation and installation of the fatty chain on the nonreduci ng terminus via selective removal of TCP led to a late intermediate wh ich was deprotected in high yield to afford the natural product.