Michio Namikoshi

Seven new meroditerpenoids, strongylophorines 13–19 (1–7), have been isolated together with the four known strongylophorines 2 (8), 3 (9), 4 (10), and 8 (11) by a screening method using oocytes of the starfish Asterina pectinifera from a marine sponge Strongylophora strongylata collected at Iriomote Island, Okinawa, Japan. The structures were assigned according to their spectral data. Ten strongylophorines inhibited the maturation of starfish oocytes in the range 1.1–37.6 μM (IC₅₀), while strongylophorine 4 (10) was not active at 250 μM.

A marine bacterium Ruegeria atlantica (designated as strain TUF-D) was isolated from a glass plate submerged in the coastal water. Three new chlorine containing compounds (1-3) together with penicillic acid (4) were obtained from a marine-derived fungus Aspergillus ostianus strain TUF 01F313 isolated from a marine sponge at Pohnpei as antibacterial components against R. atlantica. The structures of three new antibiotics were determined based on their spectral data as 8-chloro-9-hydroxy-8, 9-deoxyasperlactone (1), 9-chloro-8-hydroxy-8, 9-deoxyasperlactone (2), and 9-chloro-8-hydroxy-8, 9-deoxyaspyrone (3). Compound 1 inhibited the growth of R. atlantica at 5μg/disc (inhibition zone: 12.7mm), while 2 and 3 were active at 25μg/disc (10.1 and 10.5mm, respectively).

A new screening method to detect antimitotic substances utilizing purified porcine brain microtubule proteins was developed. This method observes the inhibitory and stimulatory activities on microtubule polymerization and inhibitory activity on depolymerization in sequence. Two glycolipids, 1-O-β-D-galactopyranosyl-2, 3-di-O-acylglycerol and 1-O-tetrahydroxycyclopentyl-2-O-acyl-3-O-alkylglycerol were isolated from Okinawan marine sponge Pseudoceratina sp. by this screening method. These compounds stimulated the microtubule polymerization at 10°C.

Two new compounds, paecilospirone (1) and phomopsidin (2), and seven known compounds, chaetoglobosin A (3), griseofulvin (4), fusarielin A (5), fusapyrone (6), deoxyfusapyrone (7), and verrucarins J (8) and L acetate (9), have been isolated and characterized from marine-derived fungi collected in tropical and sub-tropical coral reef environments. The utility of marine-derived fungi as a source of bioactive secondary metabolites is discussed.

Electrospray ionization mass spectrometry has been applied to the structure assignment of seven new microcystins (1−7), obtained from cultured Anabaena sp. strain 186. The seven new microcystins contain the dehydroalanine (Dha) or l-Ser unit instead of the N-methyldehydroalanine unit and the l-Glu and/or its δ-methyl ester [E(OMe)] units at the two variable l-amino acid units, and the structures were assigned as [Dha⁷]microcystin-E(OMe)E(OMe) (1), [d-Asp³,Dha⁷]microcystin-E(OMe)E(OMe) (2), [l-Ser⁷]microcystin-E(OMe)E(OMe) (3), [d-Asp³,l-Ser⁷]microcystin-E(OMe)E(OMe) (4), [Dha⁷]microcystin-EE(OMe) (5), [d-Asp³,Dha⁷]microcystin-EE(OMe) (6), and [l-Ser⁷]microcystin-EE(OMe) (7). These microcystins are the first examples containing dicarboxylic amino acids at the two variable l-amino acid units in microcystins.