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Kalkitoxin, a potent neurotoxin isolated from the marine cyanobacteria Lyngbya majuscula , and its congeners ( 1 – 7 ) were efficiently synthesized utilizing Hruby's diastereoselective 1,4-addition and the Wipf's oxazoline-thiazoline conversion as key steps. These synthetic efforts in combination with spectral studies of natural kalkitoxin clearly determined the absolute stereostructure of kalkitoxin to be 7 .

Five new protease inhibitors, related to aeruginosins 298-A (5), 98-A (1) and 98-B (2), were isolated from the cyanobacterium Microcystis aeruginosa. Aeruginosins 98-C (3) and 101 (4) differed from 1 in the Hpla unit. Aeruginosin 298-B (6) lacked the argininol unit in 5. Aeruginosins 89-A (7) and 89-B (8) were observed as the tautomers in HPLC because of the presence of the argininal units. Structures 3, 4 and 6–8 were determined on the basis of spectral data and chromatographic analyses of degradation products. The absolute stereochemistry of 1–8 was deduced by a combination of spectral and chemical studies. Aeruginosins 98-A to 98-C, 101, 298-A, 298-B, 89-A and 89-B were isolated from the cyanobacterium Microcystis aeruginosa. These compounds except aeruginosin 298-B had trypsin, plasmin and thrombin inhibitory activities. Their structures were determined on the basis of spectral data and amino acid analysis. Their absolute stereochemistries were deduced by a combination of spectral and chemical studies.

Three new sesquiterpene carbonimide dichlorides have been isolated from a marine sponge of the genus Axinyssa, and a guaiane-type sesquiterpene peroxide from another Axinyssa sponge. A new isocyanosesquiterpene alcohol was obtained from the nudibranch PhyUidia pustulosa. Their structures were determined on the basis of 2D NMR data. These compounds showed potent antifouling activities against larvae of the barnacle Ba/anus amphitrite.

Aeruginosins 102-A and B were isolated from the freshwater cyanobacterium Microcystis aeruginosa (NIES-102). Their structures were elucidated to be 1 and 2 on the basis of 2D NMR data and chemical degradation. These peptides inhibited thrombin potently.

Three new antifouling sesquiterpene isocyanides were isolated from nudibranchs of the family Phyllidiidae along with a new sesquiterpene peroxide and six known sesquiterpenes. Their structures were determined mainly on the basis of 2D NMR data. These compounds showed potent antifouling activity against larvae of the barnacle Balanus amphitrite .

Microviridios B and C were isolated from the freshwater blue-green alga Microcystis aeruginosa (NIES-298). Their structures were elucidated to be 1 and 2 on the basis of 2D NMR data and chemical degradation. These peptides inhibited elastase potently.