Applications of sugar nitrones in synthesis: The total synthesis of (+)-polyoxin J

A convergent synthesis of the peptidyl nucleoside antibiotic (inhibitor of chitin biosynthesis) polyoxin J (2) by coupling of 5-O-carbamoyl polyoxamic acid (3) and thymine polyoxin C (4) is described. These compounds were prepared by chain elongation and amination of sugar-derived aldehydes employing their nitrones as iminium derivatives and the furan ring as a masked carboxyl. Thus, the stereoselective addition of 2-lithiofuran to the L-threose derived N-benzyl nitrone 5 followed by reduction of the resulting hydroxylamine to amine, carbamoylation of the free hydroxy group, and oxidative cleavage of the furan ring to the carboxylate group gave a protected derivative of 3 (30%). The same method was followed for the synthesis of the ribofuranosyl alpha-amino acid nucleoside 4 (12.6%) starting from the D-ribose derived nitrone 6. The final coupling was performed by the N-hydroxysuccinimide active ester method in DMSO with the Hunig base (i-Pr2EtNH) using a derivative of 3 and unprotected 4.