Destruxins

The Alternaria black spot fungi A. brassicae and A. brassicicola produce host-selective toxins as well. While A. brassicicola produces brassicicolin A (11) as the major host-selective phytotoxin [28], A. brassicae produces destruxin B (12) (Fig. 9.4) [29]. Consistent with the virulence of these phytopathogens, both brassicicolin A (11) and destruxin B (12) appeared to be more phytotoxic to the susceptible cruciferous species B.juncea than to the tolerant B. napus. 

Scheme 32 Structure of Destruxin and Cyclization Sites within the Peptide Chain...

In 1959 Shchukina et a I. 56 showed that the addition of pyridine to DCC increases the yield (65-85%) of depsipeptides constructed from Z-protected amino acids and serine, threonine, or salicylic acid derivatives. The ferf-butyl ester of Af-(benzyloxycarbonyl)-leucylleucic acid (Table 2) was prepared in 60% yield under the same conditions of addition using a 2 molar excess of pyridine to carbodiimide. 57 The DCC/pyridine technique was successfully utilized in the ring closure between ()-alanine and leucic acid residues during the synthesis of the cyclic hexadepsipeptide destruxin B.[58 Under this modified approach the... 

Destruxin-A4 chlorohydrin (204), a depsipeptide from a Mycelium sterilium strain, induces erythropoietin gene expression 5-fold at 0.2 pM [162]. 

Cai P, Smith D, Katz B, Pearce C, Venables D, Houck D (1998) Destruxin-A4 Chlorohy-drin, a Novel Destruxin from the Fungus OS-F68576 Isolation, Structure Determination, and Biological Activity as an Inducer of Erythropoietin. J Nat Prod 61 290... 

Lira SP, Vita-Marques A, Seleghim MHR, Bugni TS, LaBarbera DV, Sette LD, Sponchiado SRP, Ireland CM, Berlinck RGS (2006) New Destruxins from the Marine-Derived Fungus Beauveria felina. J Antibiot 59 553... 

B Cyanobacteria (yanucamides A, B) [37] marine bacteria3, marine sediments3 [38]. PR Dinoflagellata (dehydro-/ -Ala, palytoxin) [36]. Fa Ascomycota Alternaria brassicae, Metarhizium anisopliae (destruxin B) [32] Hapsidospora irregularis (leualacin) [39] ... 

As pointed out above, bioassay choice is extremely important since different sensitivities and different responses are observed that are dependent on the bioassay specimen. For example, comparison of four bioassay methods for detection of destruxin B, a host-specific toxin produced by Alternaria brassicae, indicated a lack of rapid electrolyte leakage and insensitivity of host protoplasts. However, leaf and pollen bioassays were sensitive to low toxin levels. Pollen germination was the most rapid, sensitive and quantitative bioassay for the toxin. Significant inhibition of Brassica campestris pollen germination and pollen tube growth occurred only 30 min after incubation with 2.5 pg mL 1, and 7.5 pg mL 1 caused total inhibition.3... 

The cyclic depsipeptides destruxin C and D 103 and bassianolid 104 23I), which contain a-hydroxyisovaleric acid, N-methylvaline, or N-methylleucine, act as insecticides. 

Jegorov A, Sedmera P, Havlicek V, Matha V. Destruxin Ed , a cyclopeptide from the fungus Metarhizium anisoplae. Phytochemistry 49 1815-1817, 1998. 

Krasnoff SB, Gibson DM. New destruxins from the entomopathogenic fungus Aschersonia sp. J Natural Prod 59 485-489, 1996. 

The derivatives isolated so far are named destruxins after the earlier name of the fungus Oospora destructor). The conunon basic skeleton of the destruxins is a 19 membered depsipeptide ring, and the various derivatives differ from each other with respect to their side chains (55-60). 

Destruxins and bassianolide have no importance in practical plant protection because their recovery is cumbersome, they are highly toxic to warm-blooded animals and, moreover, they are not contact poisons. Their activity as a stomach poison is greatly limited by their antifeedant effect. They are primarily products of theoretical interest, and it is to be hoped that study of them will clarify relationships concerning the mechanism of the insecticidal and antifeedant effects, and will help elucidate the biological effect of cyclodepsipeptide antibiotics of similar structure. 

Destnixins. Cyclic depsipeptides from Metarrhizium anisopliae and Oospora destructor (Hyphomycetes) with insecticidal activity. Destruxin 8 is a host-specific phytotoxin from Altemaria brassicae. The D. are optically active, mostly crystalline compounds. For the most important D., see the table. 

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