Natural Product Research Vol. 23, No. 12, 15 August 2009, 1095–1107 Five naturally bioactive molecules including two rhamnopyranoside derivatives isolated from the Streptomyces sp. strain TN58 Raoudha Ben Ameur Mehdi a , Khaled A. Shaaban b , Ines Karray Rebai a , Slim Smaoui a , Samir Bejar a and Lotfi Mellouli a * a Laboratory of Prokaryotic Enzymes and Metabolites of the Centre of Biotechnology of Sfax – Tunisia (LEMP-CBS), 3038 Sfax, Tunisia; b Department of Organic and Biomolecular Chemistry, University of Go ¨ttingen, Tammannstrasse 2, D-37077 Go ¨ttingen, Germany (Received 7 July 2008; final version received 17 July 2008) Extraction of 25 L fermentation broth of the newly isolated Streptomyces sp. strain TN58 and various separation and purification steps led to the isolation of five bioactive metabolites, namely brevianamide F (C1), reported from a streptomycete for the first time, N  -acetyltryptamine (C2), thiazolidomycin (C3), and two rhamnopyranosides (C4 and C5). These two rhamnopyranosides were produced directly, without precursor addition. The chemical structure of these five active compounds was established on the basis of 1 H, 13 C/APT and 2D NMR spectra, ESI and EI-MS data, and by comparison with data from the literature. According to the biological studies, we show in this work that the compounds C1, C2, C4 and C5 possess antimicrobial activities. Keywords: Streptomyces sp. TN58; purification; chemical structure; rhamnopyranoside derivatives; antimicrobial activities 1. Introduction The development of resistance to multiple drugs is a major problem in the treatment of infections by pathogenic microorganisms. This antimicrobial resistance is presently an urgent focus of research, and new bioactive compounds are necessary to combat these pathogens. Bioactive molecules currently available can be classified in different ways based on bacterial spectrum, the type of activity (bactericidal or bacteriostatic) and the chemical structure. The latter is the most useful, and several classes of antibiotics can be distinguished, such as rhamnopyranoside derivatives, N-acetyltryptamine, thiazolidine, brevinamides, etc. Recently, several rhamnopyranoside derivatives have been extracted and identified from different species of Streptomyces (Grond et al., 2000; Grond, Papastavrou, & Zeeck, 2000, 2002; Hu et al., 2000). This kind of molecule inhibits the enzyme 3-hydroxysteroid- dehydrogenase (3-HSD), which are a useful target in the search for antiphlogistic and antitumoural agents. The secondary metabolites belonging to the N-aceyltryptamine *Corresponding author. Email: lotfi.mallouli@cbs.rnrt.tn ISSN 1478–6419 print/ISSN 1029–2349 online ß 2009 Taylor & Francis DOI: 10.1080/14786410802362352 http://www.informaworld.com Downloaded By: [University Of British Columbia] At: 14:31 30 March 2010