ABSTRACT

In the course of our investigation of biologically active substances from inedible mushrooms, we studied the chemical constituents of six species belonging to the Xylariaceae family (Sardariomycetideae) and isolated various types of azaphilone derivatives, which showed moderate to strong antimicrobial activity, such as entonaemins A−C (1−3), together with (+)-mitorubrinol acetate (4), (+)-mitorubrin (5), (+)-mitorubrinol (6), and mitorubrinic acid (7) from Entonaema splendens (Hashimoto T. and Asakawa, 1998), daldinin C (8), daldinin E, F (9, 10) from Hypoxylon fuscum (Quang et al., 2004a), cohaerins A,B (11, 12) from H. cohaerens, rubiginosin A−C (13−15) from H. rubiginosum (Quang et al., 2004b), multiformins A−D (16−19) from H. multiforme, and sassafrins A−D (20−23) from Creospharea sassafras. Their absolute structures were elucidated by 2D NMR, MS, IR, UV, CD spectra and chemical reaction (see figures on following page).
The in vitro antimicrobial activities of isolated azaphilones (1−23) at a dose of 50 μg per paper disc were tested against a panel of laboratory control strains belonging to the American Type Culture Collection, Maryland, USA: Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella enteritidis, Escherichia coli 95, and fungal organisms Aspergillus niger and Candida albicans. The disc diffusion method, according to the NC-CLS (National Committee for Clinical Laboratory Standards—Performance standards for antimicrobial disk susceptibility testing; 6^th International Supplement, Wayne Pa. 1997: M2-A6), was employed for the determination of the antimicrobial activity of the compounds. Table 1 (see next page) summarizes the antimicrobial properties of these azaphilones.
Accordingly, moderate to strong activity was observed against all tested strains. These effects, however, appear to be nonselective, because neither fungi nor bacteria remained unaffected by any of the azaphilone. They confirm previously reported bioactivities for other azaphilones and point toward the role of azaphilones as defense metabolites that may protect the stromata of Xylariaceae against feeding enemies or colonizing microbes.