1 0009-3130/19/5501-0001  2019 Springer Science+Business Media, LLC Chemistry of Natural Compounds, Vol. 55, No. 1, January, 2019 A NEW POLYKETIDE ANTIBIOTIC FROM THE MARINE BACTERIUM Streptomyces sp. PGC 32 Shabir Ahmad, 1 Mamona Nazir, 2* Muhammad Imran Tousif, 3 Muhammad Saleem, 4 Rizwana Mustafa, 2 and Tasneem Khatoon 2 A new aromatic polyketide compound, arabomycin (1), along with three known metabolites (2–4), was isolated from the culture broth of the marine bacterium Streptomyces sp. PGC 32. The structure of the new compound was established through 1D and 2D NMR analyses and high-resolution mass spectrometry, and the known compounds were elucidated on the basis of 1 H and 13 C NMR information in comparison with literature values. Arabomycin (1) was found to have potential antibacterial action against the Gram-positive bacteria Bacillus subtilis and Staphylococcus aureus, and Gram-negative bacteria Escherichia coli and Enterobacter sp. Keywords: marine bacterium Streptomyces sp., aromatic polyketide, structure elucidation, antibacterial activity. In recent years the emergence of antibiotic-resistant pathogenic bacteria has led to an increasing number of bacterial infections that are difficult to treat, which has become a leading cause of mortality [1]. To combat such infections, researchers are endeavoring to discover new natural entities from various natural sources. Marine organisms exist in an adverse environment, where the organisms have to survive under conditions of high pressure and high salt concentrations. These conditions can result in these organisms producing secondary metabolites with diverse structural features [2–4]. In the last decade, studies on the metabolites of marine bacteria have increased because of the need for new antibiotics and other economically useful compounds [5]. Previous reports have revealed that species of the Streptomyces group of bacteria are a source of novel organic compounds and have provided several antibiotics, including chloramphenicol, daptomycin, fosfomycin, lincomycin, and neomycin [6]. Recently Zhang et al. have isolated several analogues of antimycin from a marine Streptomyces sp. as cytotoxic agents [7]. Indole-derived alkaloids isolated from a marine Streptomyces sp. have been reported as potential antibiotics against Gram-positive bacteria [8]. In the present study, the EtOAc extract of the culture broth of Streptomyces sp. PGC 32 showed promising antibacterial activity and thus was subjected to chromatographic purification. As a result, the new compound arabomycin (1), along with N-[2-(4′-hydroxy-3′-methoxyphenyl)ethyl]acetamide (2) [9], 4-(2′-hydroxyethyl)- 2-methoxyphenol (3) [9], and ferulic acid (4) [10] were isolated and identified. 1) Department of Chemistry, Government Post-Graduate College, Chowk One Unit, University Road, Bahawalpur, 63100, Bahawalpur, Pakistan; 2) Department of Chemistry, Government Sadiq College Women University, Bahawalpur, 63100, Bahawalpur, Pakistan, e-mail: mamonanazir.de@gmail.com; mamonanazir.de@gscwu.edu.pk; 3) Department of Chemistry, D. G. Khan Campus, University of Education Lahore, 32200, Dera Ghazi Khan, Pakistan; 4) Department of Chemistry, Baghdad-ul-Jadeed Campus, the Islamia University of Bahawalpur, 63100, Bahawalpur, Pakistan. Published in Khimiya Prirodnykh Soedinenii, No. 1, January–February, 2019, pp. 5–7. Original article submitted July 17, 2017. O O OH OH O OH Me 1 4 12a 4a 5 5a 11a 11 6 6a 10a 10 8 12 1 DOI 10.1007/s10600-019-02602-0