Novel Type of Rigid C-Linked Glycosylacetylene−Phenylalanine Building Blocks for Combinatorial Synthesis of C-linked Glycopeptides
作者:Todd Lowary、Morten Meldal、Arnim Helmboldt、Andrea Vasella、Klaus Bock
DOI:10.1021/jo980517h
日期:1998.12.1
C-linked 3- and 4-(glycosylacetylene)-Fmoc-phenylalanines were synthesized as rigid building blocks for synthesis of libraries of neoglycopeptide templates. Perbenzylated 1,5-galactonolactone, 1,5-gluconolactone, and 1,5-mannonolactone were reacted with cerium TMS-acetylide and the products reduced to the C-glycosylacetylene-TMS derivatives. The gluco and galacto configurations yielded exclusively the beta-C-glycoside, whereas the mannonolactone gave a mixture of alpha-C- and beta-C-anomer. The products were subjected to acetolysis and TMS cleavage. The resulting peracetylated glycosylacetylenes were cross-coupled with the (R,S)-N-alpha-acetyl-3- and 4-iodophenylalanine O-methyl esters by Pd(0) catalysis in piperidine to give the eight possible C-linked glycosyl amino acid building blocks 33-40 as diastereomeric pairs. These were O-deacetylated. As an example of further conversion into neoglycopeptide templates the N-acetyl group of the 4-linked galacto-diastereomeric pair 43 was hydrolyzed selectively by acylase 1 and separated from the (R)stereoisomer. The product was converted to 4-(beta-C-galactosylacetylene)(N-alpha-Fmoc-)-L-phenylalanine (52) by reaction with Fmoc-OSu. Acid hydrolysis of galactosyl acetylene phenyl alanine 43 at elevated temperature afforded the conversion of the acetylene to the 1'-oxo derivative which was also N-alpha-Fmoc protected. The building blocks were used in the glycopeptide synthesis of three neoglycopeptide templates 54, 55, and 56 known to bind to murine MHC class II E-k and to present the glycan for interaction with the T-cell receptor. This template has previously been employed to elicit a carbohydrate specific T-cell response.