CYCLO-(HIS, LEU): A NEW MICROBIAL DIKETOPIPERAZINE FROM A TERRESTRIAL
BACILLUS SUBTILIS STRAIN B38
Salem Elkahoui, Hamdi Abdel Rahim, Olfa Tabbene, Mohamed Shaabanb, Ferid Limam and
Hartmut Laatsch
Laboratory of Bioactive Substances, Centre of Biotechnology of Borj-Cedria, Tunisia
Abstract:
Diketopiperazines are the smallest cyclic peptides. Some of their most important biological activities
are related to the inhibition of plasminogen activator inhibitor-1 and the alteration of cardiovascular
and blood-clotting functions. They also were claimed to have activities as antitumour, antiviral,
antifungal, antibacterial and antihyperglycaemic agents, and to have affinities for calcium channels
and opioid. In continuation of our search for bioactive secondary metabolites from terrestrial Bacillus spp., a new
microbial diketopiperazine, cis-cyclo-(His,Leu) was isolated from the ethyl acetate extract of a strain B. subtilis B38,
together with cis-cyclo-( Phe,Phe), tryptophane, cis-cyclo-(Leu,Tyr), cis-cyclo-(Trp,Tyr) and macrolactin A. The
chemical structures of the isolated compounds were identified by comparison of their 1D, 2D NMR and HRESIMS data
with authentic spectra and literatures. To the best of our knowledge, this is the first time that cyclo-(His, Leu) has been
isolated from natural products.