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. 2012 Feb 24;75(2):175-80.
doi: 10.1021/np2007044. Epub 2012 Jan 31.

Metacridamides A and B, macrocycles from conidia of the entomopathogenic fungus Metarhizium acridum

Affiliations

Metacridamides A and B, macrocycles from conidia of the entomopathogenic fungus Metarhizium acridum

Stuart B Krasnoff et al. J Nat Prod. .

Abstract

Metarhizium acridum, an entomopathogenic fungus, has been commercialized and used successfully for biocontrol of grasshopper pests in Africa and Australia. Its conidia produce two novel 17-membered macrocycles, metacridamides A and B, which consist of a Phe unit condensed with a nonaketide. Planar structures were elucidated by a combination of mass spectrometric and NMR techniques. Following hydrolysis of 1, chiral amino acid analysis assigned the L-configuration to the Phe unit. A crystal structure established the absolute configuration of the eight remaining stereogenic centers in 1. Metacridamide A showed cytotoxicity to three cancer lines with IC₅₀'s of 6.2, 11.0, and 10.8 μM against Caco-2 (epithelial colorectal adenocarcinoma), MCF-7 (breast cancer), and HepG2/C3A (hepatoma) cell lines, respectively. In addition, metacridamide B had an IC₅₀ of 18.2 μM against HepG2/C3A, although it was inactive at 100 μM against Caco-2 and MCF-7. Neither analogue showed antimicrobial, phytotoxic, or insecticidal activity.

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Figures

Figure 1
Figure 1
6-carbon unit consistent with COSY, HSQC, and HMBC spectra of 1. Bolded bonds indicate COSY network. Arrows indicate HMBC correlations (carbon detected by indicated proton). Double-headed arrows indicate reciprocal HMBC correlations.
Figure 2
Figure 2
Crystal structure of 1, with 50% probability thermal ellipsoids for non-H atoms.
Chart 1
Chart 1

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