Synthesis of Cairomycin-B, a novel biocyclic peptide containing Lysine and aspartic acid

Cairomycin-B, a bicyclic peptide antibiotic containing lysine and aspartic acid has been synthesised. Diketopiperazine first prepared from compound (3), deprotected and subjected to internal cyclisation using DCC and N-hydroxysuccinimid to yield the title compound (7) in 11% yield. All the intermediates and final compound have been fully characterised.