Antimalarial and antimicrobial substances isolated from the endophytic actinomycete, Streptomyces aculeolatus MS1-6

Seven undescribed compounds, including four naphthoquinone terpenoids (aculeolatins A - D), one rare 2-nitropyrrole terpenoid (nitropyrrolin F), and two hydroxamate siderophores (aculeolamides A and B) and one further undescribed compound (2,5,7-trihydroxy-3,6-dimethylnaphthalene-1,4-dione), together with eleven known compounds (arromycin, phenaziterpene A, nitropyrrolin A, heronapyrroles A and B, salaceyin A, 5,7-dihydroxy-2-isopropylchromone, 1-hydroxyphenazine, 1-methoxyphenazine, 1-acetyl-β-carboline, and N-(2-phenylethyl) acetamide), were isolated from the cultures of the endophytic Streptomyces aculeolatus MS1-6. The structures of the isolated compounds were determined using NMR spectroscopy and corroborated using chemical modification. These compounds exhibited a broad spectrum of biological activities, including antimalarial (IC₅₀ 6.03-9.84 μg/mL), antitubercular (MIC 3.13-6.25 μg/mL), anti-plant pathogenic fungal (MIC 25.0-50.0 μg/mL), and antibacterial (MIC 3.03-50 μg/mL) activities; however, they displayed unremarkable cytotoxicity against cancerous (MCF-7 and NCI-H187) and non-cancerous (Vero) cell lines.