Celogentin C (1) is a bicyclic nonribosomal peptide that was isolated from the seeds of Celosia argentea (Figure 1). It isthe most potent isolate (IC_(50) = 0.8 μm; IC = inhibitory concentration) from the celogentin/moroidin family, whose members possess inhibitory activity against tubulin polymerization. Its highly unusual architecture, which is characterized by the direct linkages of Trp C6 to Leu Cβ and Trp C2 to His N1 (Figure 1), and its biological activity have prompted a number of synthesis studies. Although N-linked His residues are known to occur in other macrocyclic peptides, the Leu-Trp linkage is extremely rare and poses a difficult synthetic challenge.
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