Antineoplastic Agents. 570. Isolation and Structure Elucidation of Bacillistatins 1 and 2 from a Marine Bacillus silvestris^,

Abstract

Two new cyclodepsipeptides designated bacillistatins 1 (1) and 2 (2) have been isolated from cultures of a sample of Bacillus silvestris that was obtained from a Pacific Ocean (southern Chile) crab. Each 12-unit cyclodepsipeptide strongly inhibited growth of a human cancer cell line panel, with GI 50 s of 10 −4 -10 −5 μg/mL, and each compound was active against antibiotic-resistant Streptococcus pneumoniae. The structures were elucidated by a combination of X-ray diffraction and mass and 2D NMR spectroscopic analyses, together with chemical degradation.Marine microorganisms are rapidly becoming a very useful source of new cancer cell growth inhibitory substances that have unique structures. Illustrative are recent examples of antineoplastic substances from marine bacteria, 1a-h fungi, 2a-h cyanobacteria, 3a-e and dinoflagellates. 4a-d As part of our extended evaluation of terrestrial and marine microorganisms as sources of new anticancer drug candidates, we collected a marine crab on Chiloé Island, Chile, in 1998. A Bacillus species, subsequently identified as B. silvestris, was isolated from the crab, and extraction of the scaled up bacterial broth has led to the identification of two new cyclodepsipeptides with antibacterial and human cancer cell line inhibitory activity. Bioactive cyclodepsipeptides have been isolated previously from other Bacillus species, including B. cereus ,5a, d B. polymyxa ,5c and B. natto. 5b Members of the genus Bacillus are common in both terrestrial and marine sediments. Bacillus silvestris was first described in 1999, when it was isolated from a sample of forest soil in Germany, 6a and more recently it was identified in water samples taken from the southern Baltic Sea, a brackish environment. 6b Results and DiscussionThe Bacillus silvestris culture was scaled up and extracted as described in the Experimental Section to give a dark-brown gum (3.14 g; P388 lymphocytic leukemia: ED 50 0.0066 μg/mL), which was shown by HPLC analysis to comprise a mixture with at least six closely spaced peaks. Subsequent high-resolution LC-MS showed the mixture to be more complex than was apparent from the HPLC analysis (Table 1).Attempts at separation by way of gel permeation and partition chromatography using Sephadex LH-20 and silica gel Lobar C 8 columns were unsuccessful. Separation using an Ito multi-layer † Dedicated to Dr. David G. I. Kingston of Virginia Polytechnic Institute and State University for his pioneering work on bioactive natural products. ‡ Dedicated also to Diane Middlebrook Djerassi (1939Djerassi ( -2007 Table 1 shows that 1 and 2 have molecular weights a little higher than that of the antibiotic valinomycin (3).By X-ray crystallographic analysis of 1 (Figure 1), its structure was shown to be a 36-membered cyclodepsipeptide that incorporates R-valine (R-Val), S-lactic acid, (S-Lac), S-valine (S-Val), and 2R-hydroxy-3S-methyl-valeric acid (2R-Hy-3S-Me-v) and that closely resembles 3, which consists of three repeating sequences of R-Val, S-Lac, S-Val, and 2R-hydroxyisova...

Psychrotolerant Paenibacillus tundrae Isolates from Barley Grains Produce New Cereulide-Like Depsipeptides (Paenilide and Homopaenilide) That Are Highly Toxic to Mammalian Cells

“…These structural differences could explain the higher hydrophobicity of paenilide and homopaenilide than those of cereulide and the cereulide homolog. Recently, a 0.9-min-longer retention time was observed by RP-HPLC analysis by replacing one O-Leu residue with O-Ile in the otherwise similar 36-membered cyclodepsipeptides bacillistatins 1 and 2, produced by the marine species Bacillus silvestris (51).…”

Diversity of Secondary Metabolites from Marine Bacillus Species: Chemistry and Biological Activity

“…Two new cyclodepsipeptides designated as bacillistatins 1 ( 19 ) and 2 ( 20 ) (Figure 8) have been isolated from the culture broth of Bacillus sil v estris that was obtained from a Pacific Ocean (southern Chile) crab [30]. Each 12-unit cyclodepsipeptide ( 19 and 20 ) strongly inhibited the growth of a human cancer cell line panel, with GI 50 ’s of 10 −4 –10 −5 µg/mL, and each compound was determined to be active against antibiotic-resistant S. pneumoniae .…”

Antineoplastic Agents. 590. X-ray Crystal Structure of Dolastatin 16 and Syntheses of the Dolamethylleuine and Dolaphenvaline Units

“…17 Descriptions of the X-ray techniques utilized in our laboratory have been previously described. 18 …”