Kengo Shigetomi

Asymmetric Total Synthesis of 6-Tuliposide B and Its Biological Activities against Tulip Pathogenic Fungi

The structure-activity relationship was investigated to evaluate the antifungal activities of tuliposides and tulipalins against tulip pathogenic fungi. 6-Tuliposide B was effectively synthesized via the asymmetric Baylis-Hillman reaction. Tuliposides and tulipalins showed antifungal activities against most of the strains tested at high concentrations (2.5 mM), while Botrytis tulipae was resistant to tuliposides. Tulipalin formation was involved in the antifungal activity, tulipalin A showed higher inhibitory activity than 6-tuliposide B and tulipalin B. Both the tuliposides and tulipalins showed pigment-inducing activity against Gibberella zeae and inhibitory activity against Fusarium oxysporum f. sp tulipae. These activities were induced at a much lower concentration (0.05 mM) than the antifungal MIC values.

Purification and characterization of a tuliposide-converting enzyme from bulbs of Tulipa gesneriana.

An enzyme that catalyzes the stoichiometric conversion of 6-tuliposide into tulipalin was purified and characterized from bulbs of Tulipa gesneriana. The enzyme appeared to be a dimer, the relative molecular mass (Mr) of each subunit being 34,900; it had maximum activity and stability at neutral pH and moderate temperature. The enzyme preferentially acted on such glucose esters as 6-tuliposides, and to a lesser extent on p-nitrophenylacetate.

MurA as a primary target of tulipalin B and 6-tuliposide B.

(−)-Tulipalin B and (+)-6-tuliposide B were confirmed to inhibit MurA in vitro. However, contrary to fosfomycin, these compounds showed potent inhibitory activities against MurA overexpressing Escherichia coli, especially in the presence of UDP-GlcNAc. These observations suggest that these compounds induced bacterial cell death not through a MurA malfunction, but in such a MurA-mediated indirect manner as the inhibition of other Mur enzymes.

Zincmethylphyrins and coproporphyrins, novel growth factors released by Sphingopyxis sp., enable laboratory cultivation of previously uncultured Leucobacter sp. through interspecies mutualism

We have identified coproporphyrins including structurally new zincmethylphyrins I and III as growth factors A–F for the previously uncultured bacterial strain, Leucobacter sp. ASN212, from a supernatant of 210 l of Sphingopyxis sp. GF9 culture. Growth factors A–F induced significant growth of strain ASN212 at the concentrations of picomolar to nanomolar which would otherwise be unculturable in liquid medium or on agar plate. More interestingly, we found that the growth factors functioned as self-toxic compounds for the growth-factor producing strain GF9 at the picomolar to nanomolar levels. As a variety of bacteria could potentially produce coproporphyrins, our findings suggest that these compounds function as a novel class of signal molecules across a boundary at phylum level in the complex bacterial communities.

Cleavage of α-Dicarbonyl Compounds by Terpene Hydroperoxide

The highly reactive α-dicarbonyl compounds, glyoxal, methylglyoxal (MGO), and 3-deoxyglucosone, react with the amino groups of proteins to form advanced glycation end-products (AGEs) which have been implicated in diabetic complications, aging, and Alzheimers disease. We found that a test sample of terpinen-4-ol (T4) containing hydroperoxides showed cleaving activity toward an α-dicarbonyl compound, but that the freshly isolated pure sample did not. Prepared terpinen-4-ol hydroperoxide (T4-H) also efficiently cleaved the C-C bond of the α-dicarbonyl compounds via Baeyer-Villiger-like rearrangement and subsequent hydrolysis of an acid anhydride moiety in the rearranged product to give carboxylic acids. Other terpene hydroperoxides, as well as T4-H, showed significant cleaving activities, and all these hydroperoxides protected RNase A from the lowering of enzyme activity induced by MGO. The cleaving mechanism via Baeyer-Villiger-like rearrangement was confirmed by time-interval NMR measurements of the reaction mixture of the symmetrical α-dicarbonyl compound, diacetyl with T4-H.

(+)-Epogymnolactam, a novel autophagy inducer from mycelial culture of Gymnopus sp.

Mushrooms, including Ganoderma lucidum, have been used as a potential source of therapeutic compounds, and an autophagy inducer would be useful for treatment of diverse diseases in human. Reported here is a full account of screening, isolation, structural determination, and biological activity of an autophagy inducer, (+)-epogymnolactam (1) from a mycelial culture of a Gymnopus sp. strain. Its structure was elucidated by HR-ESI-MS, NMR, and its plus sign by specific rotation. It exists as a tautomeric mixture of 1a and 1b in MeOH. The major tautomer of 1 is (1R,5S)-4-butyl-4-hydroxy-3-aza-6-oxa-bicyclo[3.1.0]hexan-2-one (1a), and the minor tautomeric form is (2R,3S)-3-pentanoyloxirane-2-carboxamide (1b).

First total synthesis of (+)-epogymnolactam, a novel autophagy inducer

A novel autophagy inducer, (+)-epogymnolactam (1), was first synthesized from cis-4-benzyloxy-2-butene-1-ol (2) in eight steps. A reliable preparation of optically pure epoxy alcohol (+)-3 from monobenzyl derivative (2) was established by a tandem strategy, Sharpless epoxidation/lipase kinetic resolution.

Maillard Reaction Inhibitors Produced by Paecilomyces sp.

Maillard reaction inhibitors could be useful therapeutics for diabetes and other age-related diseases. We isolated for the first time 4-O-demethylsilvaticol (1) and (−)-mitorubrin (2) as Maillard reaction inhibitors from Paecilomyces sp. 3193B. Among the isolated inhibitors, 2 showed most potent inhibitory effect by an SDS–PAGE assay on cross-linked protein formation and by a fluorescent assay on AGE formation.

Inhibitory activities of tree bark extracts against AGEs formation and their correlation with phenolic components

Advanced glycation end-products (AGEs) are one of the pivotal factors that cause a variety of diabetes complications. To explore a new class of natural resources that can prevent AGEs formation, the inhibitory activities of tree bark extracts against AGEs formation were evaluated. Most of the crude extracts of inner or outer bark showed equal or superior inhibitory activities to aminoguanidine, a conventional AGEs formation inhibitor. The quantification of phenolic components of each bark extract revealed that proanthocyanidins were one of the principal factors for inhibition, whereas flavonoids, such as flavones/flavonols and flavanones/dihydroflavonols were not a major factor. This study focused on the outer bark extract from Betula platyphylla which showed exceptionally high activity despite its low contents of total phenolics and proanthocyanidins. The bioassay-guided isolation revealed that betulin caffeate and its two derivatives were active principles in extract of B. platyphylla. These compounds exhibited up to ninefold higher activity than methyl caffeate, which suggested that betulin moiety plays a synergistic role in the activity. These results demonstrated the potency of bark extract as the screening source of AGEs inhibitors and also provided a new insight for the exploration of anti-AGEs substances from natural resources.