Four maleic anhydride derivatives, tricladolides A–D (1–4), and three alkylidene succinic acid derivatives, tricladic acids A–C (5–7), were isolated from the aquatic hyphomycete Tricladium castaneicola. The structures of these compounds were determined by spectroscopic analysis, and all were found to be novel. The compounds exhibited inhibitory activity against fungi, particularly Phytophthora sp., a plant pathogen of oomycetes. The inhibitory activity of these metabolites revealed the importance of the cyclic anhydride structure and the lipophilicity of the alkyl side chain. On the other hand, the cytotoxicity of the compounds against B16 melanoma cells indicated that the cyclic anhydride structure was not essential.

Using B16 melanoma cells for screening, we found that a marine sponge extract has a potent anti-pigmenting effect and identified arenarol as its major active compound. In normal human melanocytes (NHMs), arenarol significantly abrogated the endothelin 1 (EDN1) stimulated expression of tyrosinase, tyrosinase-related protein 1 and dopachrome tautomerase at the transcriptional, translational and enzymatic activity (only for tyrosinase) levels. That effect was accompanied by the attenuation of the increased expression level of microphthalmia-associated transcription factor (MITF) protein at the transcriptional and translational levels. Analysis of EDN1 signaling demonstrated that arenarol significantly suppressed the EDN1-induced phosphorylation of MEK, ERK, MITF and CREB but not of Raf-1s. In contrast, the forskolin-induced phosphorylation of CREB was not down-regulated by arenarol. As for the mode of action of the suppressed phosphorylation of MEK, Raf-1 activity was not directly inhibited by arenarol in vitro and pretreatment with the protein phosphatase inhibitor okadaic acid did not affect the down-regulated phosphorylation of MEK that was induced by arenarol in NHMs. The sum of these findings suggests that arenarol abrogates the EDN1-stimulated expression of melanocyte-specific proteins by interrupting MEK phosphorylation in an as yet unknown Raf-1 inactivation mechanism.

The mating hormones α1 and α2 induce sexual reproduction of the phytopathogenic genus Phytophthora. To demonstrate the structural elements responsible to hormonal activity, 17 derivatives of α1 and α2 were synthesized and their hormonal activity (oospore-inducing activity) was evaluated. The terminal ester derivatives of α1 (diacetate and dibenzoate) retained the hormonal activity, whereas a dicarbamate derivative completely suppressed the activity. Even monocarbamates showed weak activities; among them the 1-O-carbamate was less active than 16-O-carbamate, suggesting that the 1-OH group is a little more important than 16-OH. Dihydro, dehydro, and demethyl derivatives exhibited the minimum level of activity. Surviving activity of 15-epi-α1 suggested a less importance of this stereochemistry. Contrary to α1, not only the terminal diacetate derivative but also monoacetates of α2 exhibited no or little activity. Among the monoacetates, 1-O-acetyl-α2 exhibited little yet relatively better activity than the others. No activity was observed for mono- and dicarbamoyl derivatives of α2. Dihydro α2 with the saturated double bond lost most of the activity. These findings suggest that both the mating hormones α1 and α2 require most of the functional (hydroxyl, keto, and olefinic) groups they possess in their natural form for inducing the sexual reproduction of Phytophthora.

Five new steroid glycosides, linckosides M–Q (1–5), and two known related metabolites, mimics and/or enhancers of the neuritogenic activity of nerve growth factor (NGF), have been isolated from the Okinawan blue starfish Linckia laevigata. Their structures, including stereochemistry, were elucidated by spectroscopic methods and chemical derivatization. The most active metabolite linckoside P (4) induced neurite outgrowth in 55% of PC12 cells 6 days after treatment. Linckosides M–O (1–3) were less active, in the range 21 to 32%. The monoglycosides, linckoside Q (5) and the two known metabolites, 6 and 7, were much less active than the bisglycosides. All the metabolites enhanced the neuritogenic activity of a trace amount of NGF, from 11% to 60–99% three days after treatment. These structure–activity relationships suggest the importance of xylose on a side chain, especially at the C-24 carbon branch rather than at the terminal C-26, for NGF-mimic activity.

The stereochemistry of α1, the first identified mating hormone of the plant pathogen Phytophthora, has been unknown due to its acyclic flexible nature. Here, two stereogenic centers of α1 are determined to be (3RS,15R)-configuration by NMR analysis of the Mosher’s esters of α1 and a synthetic model compound. The information obtained here will be helpful for reducing the burden of the researchers who are trying to synthesize all the possible stereoisomers of α1 to elucidate its full stereochemistry.(S)-4-[(tert-Butyldiphenylsilyl)oxy]-2-methylbutanalC21H28O2SiEe = 100%[α]D28=+10 (c 0.13, CHCl3)Source of chirality: commercial starting materialAbsolute configuration: (S)(S)-1-[(tert-Butyldiphenylsilyl)oxy]-3-methyl-4-octanoneC25H36O2SiEe = 100%[α]D26=+8.0 (c 0.13, CHCl3)Source of chirality: commercial starting materialAbsolute configuration: (S)(S)-1-Hydroxy-3-methyl-4-octanoneC9H18O2Ee = 100%[α]D25=-7.7 (c 0.25, CHCl3)Source of chirality: commercial starting materialAbsolute configuration: (S)

Abstract

Water molds of the genus Phytophthora include many plant pathogens responsible for epidemics such as potato blight and sudden oak death, causing global economic damages. Sexual reproduction is of biological importance in Phytophthora and has been believed to be stimulated by unknown endogenous factors named a hormones. We describe here the chemical characterization of a Phytophthora mating hormone, a1, which was obtained from ~2 tons of culture fluid of one mating type of a species and which induced sexual spores on the counter-mating type at a nanogram level.

Two novel tetrabrominated benzofuran derivatives, named iantherans A and B, were isolated from an Australian marine sponge of the genus Ianthella. The unique structures comprised of 2,3-bis(sulfooxy)-1,3-butadiene and two brominated benzofuran moieties were determined by spectroscopic and chemical methods. Iantheran A has a (Z,Z)-1,3-butadiene moiety, whereas iantheran B is the geometric isomer possessing a (Z,E)-1,3-butadiene moiety. The inhibitory activities of the iantherans and their derivatives against Na,K-ATPase as well as the efficacy of iantheran A against other several enzymes were evaluated.