Bioactive sulfur-containing sulochrin dimers and other metabolites from an Alternaria sp. isolate from a Hawaiian soil sample

Abstract

Polluxochrin (1) and dioschrin (2), two new dimers of sulochrin linked by thioether bonds, were purified from an Alternaria sp. isolate obtained from a Hawaiian soil sample. The structures of the two metabolites were established by NMR, mass spectrometry data, and X-ray analysis. Metabolite 1 was determined to be susceptible to intramolecular cyclization under aqueous conditions, resulting in the generation of 2 as well as another dimeric compound, castochrin (3). An additional nine new metabolites were also obtained, including four new pyrenochaetic acid derivatives (8-11), one new asterric acid analogue (13), and four new secalonic acid analogues (14-17). Bioassay analysis of these compounds revealed 1-3 displayed antimicrobial and weak cytotoxic activities.

Chart 1

Figure 1

ORTEP structure generated from the X-ray diffraction data for a single crystal of 2.

Figure 2

Selected ¹H–¹H COSY and HMBC correlations for compounds 7–11.

Figure 3

ORTEP structure generated from the X-ray diffraction data for a single crystal of 7.

Figure 4

Calculated and experimental ECD data for compounds 7 (A) and 10 (B).

Figure 5

Selected ¹H–¹H COSY and HMBC correlations for compounds 14–17.