Bioassay-guided investigation of the cyanobacterium Anabaena compacta extracts afforded spumigin J (1) and the known thrombin inhibitor spumigin A (2). The absolute configuration of 1 was analyzed by advanced Marfey's methodology. Compounds 1 and 2 inhibited thrombin with EC(50) values of 4.9 and 2.1 μM, and 0.7 and 0.2 μM in the cathepsin B inhibitory assay, respectively. The MM-GBSA methodology predicted spumigin A with 2S-4-methylproline as the better thrombin inhibitor.

Aeruginosin 298-A was isolated from the freshwater cyanobacterium Microcystis aeruginosa (NIES-298) and is an equipotent thrombin and trypsin inhibitor. A variety of analogs were synthesized to gain insight into the structure-activity relations. We developed a versatile synthetic process for aeruginosin 298-A as well as several attractive analogs, in which all stereocenters were controlled by catalytic asymmetric phase-transfer reaction promoted by twocenter asymmetric catalysts and catalytic asymmetric epoxidation promoted by a lanthanide-BINOL complex. Furthermore, serine protease inhibitory activities of aeruginosin 298-A and its analogs were examined. P roteolytic reactions control many important biologic processes; thus, the discovery of new selective proteolysis inhibitors continues to receive significant attention (1). Several serine proteases have been selected as potential therapeutic targets, such as the coagulation enzyme factors Xa, VIIa, and IIa (thrombin) (2) and urokinase-type plasminogen activator (3-5). The catalytic sites of the different serine proteases involved have a highly homologous region (2); therefore, engineering high selectivity would be especially challenging. Cyanobacteria produce several unique biologically active peptides, such as microcystins, microviridin, nodularin, and puwainaphycins. Aeruginosin 298-A (1a) was isolated by Murakami and coworkers from the freshwater cyanobacterium Microcystis aeruginosa (NIES-298) (6) and is an equipotent thrombin and trypsin inhibitor (7) (Fig. 1). Since 1994, Ͼ10 aeruginosins have been isolated by Murakami (6-9), along with microcin SF608, which was isolated by Carmelli and coworker (10). These compounds have a tetrapeptide-like structure including nonstandard ␣-amino acids such as 3-(4-hydroxyphenyl)lactic acid (Hpla) and 2-carboxy-6-hydroxyoctahydroindole (Choi). Of the aeruginosin family, aeruginosin 102-A (1b) is reported to have the highest activity (7,8). More potent analogs in terms of selectivity and activity, however, need to be developed. Although the total synthesis of 1a was reported by Bonjoch et al. (11,12) and Wipf and Methot (13), the development of a highly versatile synthetic method is required to gain insight into the structure-activity relations by the syntheses of a variety of analogs. To address this issue, we applied asymmetric phase-transfer catalysis (PTC) promoted by two-center catalysts, which were recently developed by our group (14), to the syntheses of 1a as well as its analogs. Here, we report the enantioselective syntheses of aeruginosin 298-A and its analogs (15) by using asymmetric PTC and the catalytic asymmetric epoxidation of an ␣,␤-unsaturated imidazolide, which was also recently developed by our group (16)(17)(18)(19)(20)(21)(22). Moreover, serine protease inhibitory activities of 1a and its analogs were examined, leading to the future discovery of analogs possessing higher and more selective protease inhibitor potencies than those of the natural products. The knowledge gained provides important inform...

Micropeptins C (1), D (2), E (3), and F (4) have been isolated from the freshwater cyanobacterium Microcystis aeruginosa (NIES-100). The structures were elucidated by analyses of MS, NMR spectra, and chemical degradation. Micropeptins C, D, E, and F inhibited chymotrypsin with IC(50)'s of 1.1, 1.2, 1.0, and 1.5 microg/mL, respectively.