Hiroyuki Onuki

Notoamides F-K, prenylated indole alkaloids isolated from a marine-derived Aspergillus sp.

Six new prenylated indole alkaloids, named notoamides F-K (8-13), were isolated from a marine-derived Aspergillus sp. Their structures, including absolute configurations, were elucidated by spectroscopic methods. Notoamide I (11) showed weak cytotoxicity against HeLa cells with an IC(50) value of 21 microg/mL.

Two sesquiterpene isocyanides and a sesquiterpene thiocyanate from the marine sponge Acanthella cf. cavernosa and the Nudibranch Phyllidia ocellata

Abstract Three new antifungal sesquiterpenoids, cavernoisonitrile (1), cavernothiocyanate (2), and 10α-isocyano-4-amorphene (3), have been isolated from the marine sponge Acanthella cf. cavernosa, and their structures were elucidated on the basis of spectroscopic data. The nudibranch Phyllidia ocellata also contained 2 and 3.

Chemical and genetic study of Ligularia duciformis and related species in Sichuan and Yunnan Provinces of China.

The chemical constituents of the root extracts and the evolutionarily neutral DNA base sequences were studied for 28 samples of Ligularia duciformis, L. kongkalingensis, and L. nelumbifolia collected in Sichuan and Yunnan Provinces of China. The samples could be classified into four chemotypes (1–4). Sesquiterpenoids having eremophilane and oplopane skeletons were isolated from two (Chemotype 1) and three (Chemotype 2) samples, respectively. Two new oplopane derivatives were isolated and their structures were determined. In 18 samples, phenylpropenoids were the major components (Chemotype 3). In five samples, neither phenylpropenoids nor sesquiterpenoids were found (Chemotype 4). Despite this large chemical variety, no correlation was found between the chemotype and the morphological criteria of species identification. The analysis of the evolutionarily neutral DNA regions also indicated that the samples were not separated into distinct clades and that introgression was extensive.

Chemical Constituents and Diversity of Ligularia lankongensis in Yunnan Province of China

The chemical constituents of the roots of Ligularia lankongensis collected at seven different places in Yunnan Province, China, were investigated together with the DNA sequence of the atpB- rbcL intergenic region. All the samples contained a new, highly oxygenated bisabolane-type sesquiterpene ( 1). Four other oxygenated bisabolanes ( 2 and the new 3, 4, and 5) were also obtained. Intraspecific diversity was observed in the composition of the compounds, but not in the DNA sequence.

The identification of D-tryptophan as a bioactive substance for postembryonic ovarian development in the planarian Dugesia ryukyuensis

Many metazoans start germ cell development during embryogenesis, while some metazoans possessing pluripotent stem cells undergo postembryonic germ cell development. The latter reproduce asexually but develop germ cells from pluripotent stem cells or dormant primordial germ cells when they reproduce sexually. Sexual induction of the planarian Dugesia ryukyuensis is an important model for postembryonic germ cell development. In this experimental system, hermaphroditic reproductive organs are differentiated in presumptive gonadal regions by the administration of a crude extract from sexual planarians to asexual ones. However, the substances involved in the first event during postembryonic germ cell development, i.e., ovarian development, remain unknown. Here, we aimed to identify a bioactive compound associated with postembryonic ovarian development. Bioassay-guided fractionation identified ʟ-tryptophan (Trp) on the basis of electrospray ionization–mass spectrometry, circular dichroism, and nuclear magnetic resonance spectroscopy. Originally masked by a large amount of ʟ-Trp, ᴅ-Trp was detected by reverse-phase high-performance liquid chromatography. The ovary-inducing activity of ᴅ-Trp was 500 times more potent than that of ʟ-Trp. This is the first report describing a role for an intrinsic ᴅ-amino acid in postembryonic germ cell development. Our findings provide a novel insight into the mechanisms of germ cell development regulated by low-molecular weight bioactive compounds.

Mechanism of hemolysis and erythrocyte transformation caused by lipogrammistin-A, a lipophilic and acylated cyclic polyamine from the skin secretion of soapfishes (Grammistidae)

The mechanism of hemolysis and erythrocyte transformation caused by lipogrammistin-A (LGA), a lipophilic and acylated cyclic polyamine from the skin secretion of soapfishes (Grammistidae), was investigated. The dependency of hemolysis on the erythrocyte concentration indicated that the amount of membrane-bound LGA required for 50% hemolysis is about 13% of the total phospholipids in erythrocytes on a molar basis. A synthetic analogue which lacked a long alkyl chain exhibited much less activity, suggesting that the alkyl chain is important for membrane-binding. In addition, microscopic observations showed that LGA elicited the invagination of erythrocytes at sublytic concentrations, which makes LGA one of the most potent agents with this transforming activity known to date. Its protonated secondary amino group is responsible for the unequal distribution of LGA in the inner leaflet of the lipid bilayer, which leads to invagination, since acetylation at the amino group markedly reduced the invagination activity. Furthermore, the size of LGA-induced lesions on erythrocyte membrane was estimated to be 7-29 A based on osmotic protection experiments, where the external addition of isotonic molecules in this size range gradually increased the effective dose of LGA. Based on these lines of evidence, the mode of LGA action on erythrocytes is deduced to be as follows. First, LGA molecules bind to erythrocyte membrane by lipophilicity. Second, the molecules accumulate in the inner leaflet of the lipid bilayer by interaction of their cationic ammonium groups with acidic residues of membrane lipid in the inner surface. This uneven distribution of LGA distorts the bilayer structure, and results in a change in cell shape and consequent small lesions. Third, small solutes permeate through the lesions, which induces an osmotic change across the membrane, which leads to colloid-osmotic rupture. This mode of action of LGA on erythrocytes accompanied by cell invagination is the first reported example for natural defense substances.