Haruki Niwa

Ptaquiloside, a novel norsesquiterpene glucoside from bracken, Pteridium aquilinum var. latiusculum

An unstable norsesquiterpene glucoside with a novel illudane skeleton, ptaquiloside (1) has been isolated from bracken fern, Pteridium aquilinum var. latiusculum and the planar structure has been established on the basis of spectral and chemical means.

Ptaquiloside, a potent carcinogen isolated from bracken fern pteridiumaquilinum var. latiusculum: structure elucidation based on chemical and spectral evidence, and reactions with amino acids, nucleosides, and nucleotides

Abstract The structure of ptaquiloside (1), a potent carcinogenic compound isolated from bracken fern, Pteridium aquilinum var. latiusculum has been elucidated on the basis of chemical and spectral evidence. The dienone 3 generated from 1 under alkaline conditions was shown to be a strong alkylating agent. For the purpose of obtaining the preliminary information on chemical modification of biopolymers such as proteins and DNA with the dienone 3, reactions of 3 with amino acids, nucleosides, and nucleotides have been carried out and the alkylated products have been characterized.

Halicholactone and neohalicholactone, two novel fatty acid metabolites from the marine sponge halichondria okadai kadota

Halicholactone (1) and neohalicholactone (2), unusual fatty acid metabolites having a cyclopropane ring and a nine-membered lactone were isolated from the marine sponge Halichondria okadai Kadota. The planar structures of the new metabolites were elucidated on the basis of spectral and chemical means.

Separation of carcinogenic fraction of bracken fern

Isolation of the carcinogen in the boiling water extract of bracken fern was conducted by following the active principle with a carcinogenicity bioassay. Fractionation of the bracken extract was carried out using adsorption on resin (Amberlite XAD-2 and TOYOPEARL HW-40 (c] and organic solvent extraction. A diet containing each of the fractions was given to 7 female Charles River Sprague-Dawley rats (CD rats) of 4 weeks old, except for the second fraction. All 7 rats given the last carcinogenic fraction developed mammary and intestinal tumors and 5 rats had urinary bladder tumors. Ptaquiloside (PT) which induced mammary cancer in female CD rats and rho-hydroxystyrene glycosides were isolated from this fraction.

A new method for cleavage of aliphatic methyl ethers

Abstract A new efficient procedure for the cleavage of aliphatic methyl ethers under the mild conditions by the use of the reagents system, boron tribromide - sodium iodide - 15-crown-5 is described.

Stereochemistry of ptaquiloside, a novel norsesquiterpene glucoside from bracken, Pteridium aquilinum var. latiusculum

Abstract The absolute stereostructure of ptaquiloside ( 1 ), a novel norsesquiterpene glucoside isolated from bracken, Pteridium aquilinum var. latiusculum has been elucidated by the 1H NMR spectral method and an X-ray crystallographic analysis of ptaquiloside tetraacetate ( 2 ).

The three-dimensional structure of neohalicholactone, an unusual fatty acid metabolite from the marine sponge halichondria okadai kadota

The three-dimensional structure of the unusual fatty acid metabolite neohalicholactone, isolated from the marine sponge Halinchondria okadai Kadota, has been determined by X-ray crystallography.

Laurencenyne, a plausible precursor of various nonterpenoid C15-compounds, and neolaurencenyne from the red alga laurencia okamurai

Structural elucidation of two new acetylenic polyenes, laurencenyne 5 and neolaurencenyne 6 isolated from Laurencia okamurai, together with their syntheses, was achieved, suggesting that laurencenyne 5 was a possible precursor of various nonterpenoid C15-compounds in the marine red algae of the genus Laurencia.

Alkylation of nucleosides by dehydromonocrotaline, the putative toxic metabolite of the carcinogenic pyrrolizidine alkaloid monocrotaline

Abstract Reaction of dehydromonocrotaline (3), the putative toxic metabolite of the carcinogenic pyrrolizidine alkaloid monocrotaline (2), with various nucleosides proceeded mostly at the C-9″ position of 3 to give several nitrogen atom-alkylated nucleosides including N-7 alkylated 2′-deoxyguanosine 14.

Isolation of (10R,11R)-(+)-squalene-10,11-epoxide from the red alga laurencia okamurai and its enantioselective synthesis

Abstract (10 R ,11 R )-(+)-Squalene-10,11-epoxide 1 has been isolated from the red alga Laurencia okamurai . On the basis of the spectral data and comparison to the racemic compound prepared from squalene, assignment of the planar structure was made. The enantioselective synthesis of 1 was performed, which determined the absolute stereochemistry of 1 .