Secondary metabolites from a marine-derived endophytic fungus Penicillium chrysogenum QEN-24S

Abstract

Penicillium chrysogenum QEN-24S, an endophytic fungus isolated from an unidentified marine red algal species of the genus Laurencia, displayed inhibitory activity against the growth of pathogen Alternaria brassicae in dual culture test. Chemical investigation of this fungal strain resulted in the isolation of four new (1-3 and 5) and one known (4) secondary metabolites. Their structures were identified as two polyketide derivatives penicitides A and B (1 and 2), two glycerol derivatives 2-(2,4-dihydroxy-6-methylbenzoyl)-glycerol (3) and 1-(2,4-dihydroxy-6-methylbenzoyl)- glycerol (4), and one monoterpene derivative penicimonoterpene (5). Penicitides A and B (1 and 2) feature a unique 10-hydroxy- or 7,10-dihydroxy-5,7-dimethylundecyl moiety substituting at C-5 of the α-tetrahydropyrone ring, which is not reported previously among natural products. Compound 5 displayed potent activity against the pathogen A. brassicae, while compound 1 exhibited moderate cytotoxic activity against the human hepatocellular liver carcinoma cell line.

Keywords: Penicillium chrysogenum; marine endophyte; secondary metabolites.

Figure 1

P. chrysogenum QEN-24S inhibitory activity against growth of the pathogen fungus A. brassicae.

Figure 2

Structures of the isolated compounds 1–5 and the reference compounds 6 and 7.

Figure 3

Key ¹H-¹H COSY (bold lines) and HMBC (arrows) correlations of compounds 1, 3 and 5.

Figure 4

Comparison of ¹³C-NMR chemical shifts (in CDCl₃) of 1 with two analogues (a and b) to establish the relative configurations at C-3 and C-5 in 1.

Figure 5

Values of Δδ_H(S–R) (measured in CDCl₃) of the MTPA esters (α-methoxy-α-(trifluoro-methyl)phenylacetate) of compound 1.