Pyramidamycins A-D and 3-Hydroxyquinoline-2-carboxamide; Cytotoxic Benzamides from Streptomyces sp. DGC1

Four new benzamides, pyramidamycins A-D (2–5) along with the new natural 3-hydroxyquinoline-2-carboxamide (6) were isolated from the crude extract of Streptomyces sp. DGC1. Additionally, five other known compounds namely 2-aminobenzamide (anthranilamide) (1), 4′,7-dihydroxyisoflavanone (7), 2′-deoxy-thymidine, 2′-deoxy-uridine and adenosine were also isolated and identified. The structures of the new compounds 2–6 were elucidated by 1D and 2D NMR studies along with HRMS analyses. The isolated compounds 1–6 contained the same amide side chain. The isolated compounds 1–7 were biologically evaluated in comparison with landomycin A against a prostate cancer cell line (PC3) and non small cell lung cancer cell line (H460) for 48 hrs and against several bacterialstrains. Pyramidamycin C (4) was the most active compound against both PC3 and H460 cell lines (GI(50) = 2.473 μM and GI(50) = 7.339 μM, respectively). Benzamides (1–3) demonstrated inhibitory activity against Kocuria rosea B-1106 (a diameter halo of 13±2 mm for 1; 10±2 mm for 2 and 3). Compound 6 was slightly active against both Escherichia coli DH5α and Micrococcus luteus NRRL B-2618 (diameter halos 8±2 mm and 9±2 mm, respectively). Taxonomically, the amplified 500 bp 16S rRNA fragment of the Streptomyces sp. DGC1 had 99% identity (BLAST search) to the 16S rRNA gene of Streptomyces atrovirens strain NRRL B-16357.