Published papers

An unusual nucleoside, 4-amino-7-(5′-deoxy-β-D-xylofuranosyl)-5- iodopyrrolo[2,3-d]pyrimidine (1), was isolated from an ascidian, Diplosoma sp., and its structure was successfully determined by spectroscopic and chemical analysis. The known didemnenones 2-5 were also isolated. Compound 1 was found to inhibit the division of fertilized sea urchin eggs.

Mycalolide B, a cytotoxic macrolide isolated from a marine sponge of the genus Mycale, has an actin depolymerizing activity. This paper reports the synthesis of C7-C35 fragment of mycalolides via cross olefin metathesis reaction between trisoxazole fragment and side-chain fragment.

A potent growth inhibitor was isolated from blue light-illuminated sunflower (Helianthus annuus) hypocotyls and identified as 8-(β-D-glucopyranosyloxy)-3-hydroxy-1,9,14-pentadecatriene-4,6-diyne (1, designated "helian") from analysis of its 1H and 13C NMR spectra, and HRFABMS. Helian 1 showed plant growth-inhibitory activity at concentrations higher than 2.6 × 10-6 mol/L for the cress root growth test. The amount of helian was higher in the illuminated halves than in the shaded ones in phototropically stimulated sunflower hypocotyls. These results suggest that this new potent growth inhibitor, helian, may play an important role on phototropism of sunflower hypocotyls.

Aplyronine A 1 is a potent antitumor macrolide isolated from the sea hare Aplysia kurodai. Aplyronine A interacts with actin, one of the major proteins in cytoskeleton. We achieved total synthesis of aplyronine A and its 18 analogs and investigated structure-activity relationships. Analysis of the interaction of aplyronine analogs with actin by a photoaffinity labeling method and X-ray crystal structure analysis of actin complex with aplyronine A have been carried out. These results revealed that aplyronine A binds to actin at the hydrophobic cleft between subdomains 1 and 3 of actin. The binding mode of the macrolactone part of aplyronine A was different from previously reported macrolides. In addition, the trimethylserine moiety of aplyronine A, the essential functional group for cytotoxicity against HeLa S3 cells, was sticking out from a surface of actin-aplyronine A complex.

Mycalolide analog 4, consisting only of the side chain of mycalolide B (2), a trisoxazole macrolide of marine origin, was stereoselectively synthesized using Roush crotylboration, an Evans aldol reaction, and a Paterson aldol reaction as key steps. The analog 4 was found to have strong actin-depolymerizing activity.

The enantioselective synthesis of aurisides A and B, macrolide glycosides of marine origin, was achieved by a convergent approach. The C1-C9 segment 4 was prepared from (R)-pantolactone, and the C10-C17 segment 14 was synthesized from (R)-glycidyl trityl ether. The Nozaki-Hiyama-Kishi reaction between 4 and 14 and subsequent reactions gave seco acid 10, which was converted into the aglycon (3) of aurisides by construction of the 14-membered lactone and bromine-substituted conjugated diene. The glycosylation reaction of the aglycon provided aurisides A and B.

Three saponins, isotheasaponins B1-B3, were isolated from the leaves of the tea plant Camellia sinensis var. sinensis, and their structures were determined to be theasapogenol B [β-d-galactopyranosyl(1 → 2)][β-d-xylopyranosyl(1 → 2)-α-l-arabinopyranosyl(1 → 3)]-β-d-gulcopyranosiduronic acid with two acyl groups by spectroscopic analysis.

The interaction between actin and aplyronine A, a potent antitumor and actin-depolymerizing substance of marine origin, was investigated by photoaffinity labeling experiments. Photoaffinity probes consisting of a side-chain portion of aplyronine A as a ligand, a diazirine moiety as a photoaffinity group, and a fluorophore as a detecting group were synthesized. Photolabeling experiments between actin and the probe were carried out. Actin was successfully photolabeled by the fluorescent probe and visualized clearly. The present results provide the first chemical evidence for the direct interaction between actin and the side-chain portion of aplyronine A.

Aplyronine A, isolated from the sea hare Aplysia kurodai, possesses an exceedingly potent antitumor effect in vivo and it is one of the promising candidates as an anticancer drug. This macrolide is known to depolymerize F-actin and inhibit the polymerization of actin by forming a 1:1 complex with monomeric actin. The first complex structure of actin-aplyronine A was determined via a synchrotron X-ray analysis at a 1.45 Å resolution. As expected, aplyronine A binds to a hydrophobic cleft composed of subdomains 1 and 3 of actin by intercalating its aliphatic tail part into the actin molecule as do the other reported F-actin depolymerizing agents. Unexpectedly, this complex structure shows the specific structural features around the trimethylserine moiety, revealed as an important moiety of aplyronine A for cytotoxicity against HeLa cells. Combining this result and our previous one, the moiety should strongly relate to the specific biological activity of aplyronine A; i.e. a potent antitumor effect.

Plant growth inhibitory polyacetylenes have been isolated from the insect galls on flower buds of Hedera rhombea Bean (Araliaceae) formed by the ivy flower bud gall midge, Asphondylia sp. (Cecidomyiidae), and their structures elucidated by spectroscopic and chemical means. The EC50 values for roots/hypocotyls growth of cress (Lepidium sativum L.) seedlings were 7.0×10-5/8.0×10-5 M for (Z)-8-acetoxy-1,2- epoxy-3-oxoheptadeca-9-ene-4,6-diyne, 9.5×10-5/9.0×10-5 M for (Z)-8-acetoxy-3-oxoheptadeca-1,9-diene-4,6-diyne, 2.5×10-5/5. 5×10-6 M for (Z)-8-acetoxy-1-methoxy-3-oxoheptadeca-9-ene-4,6-diyne, and 7.5×10-5/2.0×10-6 M for falcarindiol, respectively. On the other hand, 8-acetoxyfalcarinol exhibited lower inhibition on roots and hypocotyls growth. Among these compounds, (Z)-8-acetoxy-1-methoxy- 3-oxoheptadeca-9-ene-4,6-diyne exhibited the strongest inhibitiory effect on root growth of cress seedlings, whereas against hypocotyl growth of cress seedlings, falcarindiol showed the strongest inhibition.

The trifluoroacetate salt of cinachyramine (1) was isolated from the Okinawan sponge Cinachyrella sp. This structure was determined by the spectroscopic analysis and the degradation under acidic conditions. Cinachyramine (1) is a novel alkaloid with an unprecedented cage system possessing a hydrazone and two aminals.

A mixture of cyclohaliclonamines A-E (1-5), novel dimeric, trimeric, tetrameric, pentameric, and hexameric 3-alkylpyridinium alkaloids, was obtained from an Okinawan sponge Haliclona sp. Cyclohaliclonamines C-E are the first tetrameric, pentameric, and hexameric 3-alkylpyridinium alkaloids from natural sources. The structure determination of cyclohaliclonamines is discussed in detail.

Maedamide, a novel chymotrypsin-inhibiting depsipeptide, was isolated from a cyanobacterial assemblage that mostly consisted of Lyngbya sp. Its structure was elucidated by spectroscopic analyses and chiral HPLC analyses of hydrolysis products. Maedamide selectively inhibited chymotrypsin but not elastase and trypsin. In addition, Maedamide strongly inhibited the growth of HeLa cells and HL60 cells.

Leucas aspera (Lamiaceae), an aromatic herbaceous plant, is well known for many medicinal properties and a number of bioactive compounds against animal cells have been isolated. However, phytotoxic substances from L. aspera have not yet been documented in the literature. Therefore, current research was conducted to explore the phytotoxic properties and substances in L. aspera. Aqueous methanol extracts of L. aspera inhibited the germination and growth of garden cress (Lepidum sativum) and barnyard grass (Echinochloa crus-galli), and the inhibitory activities were concentration dependent. These results suggest that the plant may have phytotoxic substances. The extracts were then purified by several chromatographic runs. The final purification was achieved by reversed-phase HPLC to give an equilibrium (or inseparable) 3:2 mixture of two labdane type diterpenes (compounds 1 and 2). These compounds were characterized as (rel 5S,6R,8R,9R,10S,13S,15S,16R)-6-acetoxy-9,13;15,16-diepoxy-15-hydroxy-16-methoxylabdane (1) and (rel 5S,6R,8R,9R,10S,13S,15R,16R)-6-acetoxy-9,13;15,16-diepoxy-15-hydroxy-16-methoxylabdane (2) by spectroscopic analyses. A mixture of the two compounds inhibits the germination and seedling growth of garden cress and barnyard grass at concentrations greater than 30 and 3μM, respectively. The concentration required for 50% growth inhibition (I50) of the test species ranges from 31 to 80μM, which suggests that the mixture of these compounds, are responsible for the phytotoxic activity of L. aspera plant extract.

Biselyngbyolide A is an 18-membered macrolide that exhibits significant biological activities such as growth-inhibitory activity and apoptosis inducing activity against cancer cells. In this study, the first total synthesis of biselyngbyolide A by using an intramolecular Stille coupling reaction as a key step is achieved.

Kurahamide, a new dolastatin 13 analog, was isolated from a marine cyanobacterial assemblage, consisting mostly of Lyngbya sp. Its gross structure was elucidated by spectroscopic analysis, and the stereochemistries were assigned based on a chiral HPLC analysis of hydrolysis products. Kurahamide strongly inhibited elastase and chymotrypsin in vitro. In addition, kurahamide moderately inhibited the growth of human cancer cells, including HeLa and HL60 cells.

The grass Brachiaria brizantha, native to eastern Africa, becomes naturalized and dominant quickly in the non-native areas. It was hypothesized that phytotoxic chemical interaction between this plant and native plants may play an important role in the invasion of B. brizantha. However, no potent phytotoxic substance has been reported in this species. Therefore, we investigated possible allelopathic activity and searched for phytotoxic substances with allelopathic activity in B. brizantha. An aqueous methanol extract of B. brizantha inhibited the growth of roots and shoots of garden cress (Lepidium sativum), lettuce (Lactuca sativa), timothy (Phleum pratense) and ryegrass (Lolium multiflorum) seedlings. The extract was purified by several chromatographic runs and three allelopathically active substances were isolated and identified by spectral analysis as (6R,. 9R)-3-oxo-α-ionol, (6R,. 9S)-3-oxo-α-ionol and 4-ketopinoresinol. (6R,. 9R)-3-Oxo-α-ionol and (6R,. 9S)-3-oxo-α-ionol inhibited root and shoot growth of garden cress at concentrations greater than 30 and 10. μM, respectively. The activity of (6R,. 9S)-3-oxo-α-ionol was 5.3- to 6.2-fold that of (6R,. 9R)-3-oxo-α-ionol. The stereochemistry of the hydroxyl group at position C-9 may be important for the inhibitory activities of those compounds. 4-Ketopinoresinol inhibited root and shoot growth of garden cress at concentrations greater than 30. μM. The growth inhibitory activity of (6R,. 9S)-3-oxo-α-ionol was the greatest and followed by 4-ketopinoresinol and (6R,. 9R)-3-oxo-α-ionol. These results suggest that those phytotoxic substances may contribute to the allelopathic effect caused by B. brizantha and may be involved in the invasion of B. brizantha.