Julichrome Monomers from Marine Gastropod Mollusk-Associated Streptomyces and Stereochemical Revision of Julichromes Q3 ⋅ 5 and Q3 ⋅ 3

Abstract

Two julichrome monomers, julichromes Q₁₁ (1) and Q₁₂ (2), along with five known julichromes (Q₁₀ , Q_{3 ⋅ 5} , Q_{3 ⋅ 3} , Q_{6 ⋅ 6} , Q₆ , 3-7) and four known anthraquinones (chrysophanol, 4-acetylchrysophanol, islandicin, huanglongmycin A, 8-11), were isolated from the marine gastropod mollusk Batillaria zonalis-associated Streptomyces sampsonii SCSIO 054. This is the first report of julichromes isolated from a marine source. Extensive dissection of 1D and 2D NMR datasets combined with X-ray crystallography enabled rigorous elucidation of the previously reported configurations of julichrome Q_{3 ⋅ 5} (4) and related julichrome Q_{3 ⋅ 3} (5); both of the configuration at C(9) needs to be revised. In addition, julichrome Q₁₂ (2) was found to display antibacterial activity against Micrococcus luteus and Bacillus subtilis with MICs of 2.0 and 8.0 μg mL^-1 ; four compounds (1, 3, 6, 7) also showed inhibitory activities against an array of methicillin-resistant Staphylococcus aureus, S. aureus and S. simulans AKA1 with MIC values ranging from 8 to 64 μg mL^-1 .

Keywords: absolute configuration; antibacterial activity; biological activity; julichromes; structure revision.