Antifungal Cyclic Peptide Research Articles

Synthetic studies on antifungal cyclic peptides, echinocandins. Stereoselective total synthesis of echinocandin D via a novel peptide coupling

Synthetic studies on the novel fungicidal oligopeptides, echinocandins ( 1b and 1c), are described. The constituent amino acids 5–8 were synthesized in a stereocontrolled manner from the chiral starting materials, 5a, 6a and 7a, respectively. The coupling of these amino acids was characterized by the use of unprotected amino acid as the C-terminal and 2-pyridyl thiol ester as the N-terminal, and the coupling was performed in the presence of 1-(trimethylsilyl)imidazole (TMSIm) or a catalytic amount of tert-amine to give C-terminal free dipeptides, 14 and 16a, respectively, which were converted to the pentapeptide 17a, a common intermediate for the synthesis of 1b and 1c. The synthesis of 1c was achieved by the cyclization of the hexapeptide 24b.

Antifungal cyclic peptides from the terrestrial blue-green alga Anabaena laxa. II. Structures of laxaphycins A, B, D and E.

Laxaphycins A and B are the major components in an antifungal mixture of cyclic peptides from the terrestrial blue-green alga Anabaena laxa FK-1-2. NMR and MS spectral studies coupled with amino acid analysis indicate that the gross structures of laxaphycins A and B are cyclic (Aoc-Hse-E-Dhb-Hyp-Hse-Phe-Leu-Ile-Ile-Leu-Gly) where Aoc is a 3-aminooctanoic acid residue and cyclic (Ala-Hleu-Gln-N-MeIle-Hasn-Thr-Pro-Leu-Thr-Ade-Val- Hleu) where Ade is a 3-aminodecanoyl unit, respectively. Laxaphycin E, a minor cyclic undecapeptide, differs in gross structure from laxaphycin A in possessing a 3-aminodecanoic acid unit (Ade) in lieu of Aoc, whereas laxaphycin D, a minor cyclic dodecapeptide, differs from laxaphycin B in possessing a 3-aminooctanoyl unit (Aoc) instead of an Ade unit.

Antifungal cyclic peptides from the terrestrial blue-green alga Anabaena laxa. I. Isolation and biological properties.

Laxaphycins are responsible for the antifungal and cytotoxic activity of crude ethanolic extracts from the cultured blue-green alga Anabaena laxa. These cyclic peptides exhibit an unusual biological synergism when tested for antifungal or cytotoxic effects. The isolation procedure for the peptides, their characterization and biological activities are described here along with experiments demonstrating synergism between the two major laxaphycins.