Synthesis of Orthogonally Protected Muramic Acid Building Blocks for Solid Phase Peptide Synthesis

• Main Authors: Kristina Vlahoviček-Kahlina, Andreja Jakas
• Format: Article
• Language: English
• Published: Croatian Chemical Society 2015-07-01
• Series: Croatica Chemica Acta
• Online Access: http://hrcak.srce.hr/file/209505
• ISSN: 0011-1643; 1334-417X

Muramic acid is found in many peptide natural products containing oligo(poly)saccharide moieties. Taking into consideration that the Fmoc methodology is routinely used for solid-phase peptide synthesis, preparation of orthogonally protected muramic acid building blocks for total solid-phase synthesis of these natural products is of particular practical importance. Herein a simple and efficient synthesis of benzyl 2-amino-4,6-O-benzylidene-3-O-[(R)-1-carboxyethyl]-2-deoxy-N-9-fluorenylmethyloxycarbonyl-α-D-glucopyranoside (6) from N-acetylglucosamine (1) is described. Important improvements over previous synthetic approaches to glucopyranosides 2 (benzyl 2-acetamido-2-deoxy-α-D-glucopyranoside) and 3 (benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-α-D-glucopyranoside), key building blocks in preparation of 6, include synthesis simplification and efficient isolation and purification. Optically pure (S)-2-chloropropionic acid 7 was prepared and introduced to the positon 3-O of sugar moiety to give compound 4 (benzyl 2-acetamido-4,6-O-benzylidene-3-O-[(R)-1-carboxyethyl]-2-deoxy-α-D-glucopyranoside) with the (R)-configuration of the lactyl side-chain in excellent overall yield and optical purity. Deacetylation of amino group gave compound 5 (benzyl 2-amino-4,6-O-benzylidene-3-O-[(R)-1-carboxyethyl]-2-deoxy-α-D-glucopyranoside) suitable for incorporation of the Fmoc protecting group to give protected muramic acid derivative 6, a useful building block in peptide synthesis.