The destruxins: synthesis, biosynthesis, biotransformation, and biological activity

Destruxins, secondary metabolites first reported in 1961, are cyclic hexadepsipeptides composed of an alpha-hydroxy acid and five amino acid residues. The name "destruxin" is derived from "destructor" from the species Oospora destructor, the entomopathogenic fungus from which these metabolites were first isolated. Individual destruxins differ on the hydroxy acid, N-methylation, and R group of the amino acid residues; where established, the configurations of the amino acid residues are S, and those of the hydroxy acids are R. Destruxins exhibit a wide variety of biological activities, but are best known for their insecticidal and phytotoxic activities. The great interest in destruxins derives from their potential role as virulence factors in fungi, whether such microorganisms are useful insect biocontrol agents or detrimental, causing great plant disease epidemics. Reports on isolation, chemical structure determination, total synthesis, transformation by diverse organisms, and biological activity of destruxins and related metabolites are reviewed for the first time.

Synthesis and biological evaluation of destruxin A and related analogs

This report describes the development of an efficient solid-phase synthesis protocol and adaptation of reported solution phase procedures for the synthesis of the cyclic depsihexapeptide destruxin A and related analogs. The solid-phase method described is based on standard Fmoc peptide chemistry, including a new synthetic method for the assembly of the depsi bond-containing unit. In order to select analogs of destruxin A for synthesis and evaluation of insecticidal activity, the work of Hellberg et al., describing a set of Z-descriptors for amino acid side-chains comparing their physicochemical properties, was utilized. Destruxin A and 27 different analogs with structural variations in four residues were synthesized and insecticidal activity was evaluated via injections into tobacco budworm (Heliothis virescens) larvae. Several destruxin A analogs were found to be at least as potent as the native compound.

Synthesis and biological activity of a destruxin analogue: D-Lac-6 destruxin E

A general strategy for the synthesis of destruxin analogues is described and applied to a particular example, D-Lac-6 destruxin E. The tetrapeptide Boc-Ile-N-MeVal-N-MeAla-beta-Ala-OMe (2) was chosen as the basic starting compound, and its preparation was optimized. This fragment was then coupled with the compound (D)Lac-Pro, and the resulting peptide was cyclized by the DEPC or DPPA/HOBt/DMAP methods at 21 and 30% yield, respectively. The biological activity of the analogue obtained was established by injection to an insect host.