Yukiko Kan

Macrocarpals: HIV-RTase inhibitors of Eucalyptus globulus

Abstract Five HIV-RTase inhibitors, macrocarpals A-E, have been isolated from Eucalyptus globulus . X-ray diffraction studies as well as spectral and chemical investigations established the structures 1, 2, 3, 12, and 13 , respectively.

Determination of the absolute configuration of yessotoxin, a polyether compound implicated in diarrhetic shellfish poisoning, by NMR spectroscopic method using a chiral anisotropic reagent, methoxy-(2-naphthyl)acetic acid

Abstract The absolute configuration of yessotoxin (1), a potent diarrhetic toxin causative of shellfish poisoning, was determined by NMR-spectroscopy using a chiral anisotropic reagent, methoxy-(2-naphthyl)acetic acid (2NMA), which was applied to a monoacetate of bisdesulfated yessotoxin (3).

Phenolic constituents of the liverwort: Four novel cyclic bisbibenzyl dimers from Blasia pusilla L

Abstract Four novel, cyclic, bisbibenzyl dimers (pusilatins A-D), six bibenzyl derivatives, apigenin 7-O-β- d -glucoside , shikimic acid and five orsellinic acid derivatives have been isolated from the methanolic extract of the liverwort Blasia pusilla L. and their structures characterized by a combination of spectral data, chemical modification and X-ray crystallographic analysis. The previously assigned structure of pusilatin D was revised. Pusilatins B and C showed DNA polymerase β inhibitory activity.

Zooxanthellatoxin-B, vasoconstrictive congener of zooxanthellatoxin-A from a symbiotic dinoflagellate Symbiodinium sp

Abstract Zooxanthellatoxin-B was isolated from a symbiotic marine alga, Symbiodinium sp. and the structure of zooxanthellatoxin-B was determined to be a 62-membered lactone by comparing spectral data and degradation products with those of zooxanthellatoxin-A.

Alchivemycin A, a Bioactive Polycyclic Polyketide with an Unprecedented Skeleton from Streptomyces sp.†

Alchivemycin A, a novel polycyclic polyketide, was isolated from the culture extract of a plant-derived actinomycete Streptomyces sp. The structure and relative configuration were elucidated by spectroscopic analysis and X-ray crystallography, and the absolute configuration was determined by a (1)H NMR anisotropy method using MPA ester derivatization. The new compound contains an unprecedented heterocyclic ring system, 2H-tetrahydro-4,6-dioxo-1,2-oxazine. Alchivemycin A showed potent antimicrobial activity against Micrococcus luteus and inhibitory effects on tumor cell invasion.

(+)-Cavicularin: A novel optically active cyclic bibenzyl-dihydrophenanthrene derivative from the liverwort Cavicularia densa Steph

Abstract From the methanolic extract of the liverwort Cavicularia densa a novel phenolic secondary metabolite, (+)-cavicularin (1) has been isolated. The structure was determined by extensive high field (600MHz) 2D-NMR spectra and it was confirmed by an X-ray crystallographic analysis. It was shown to be c cyclic bibenzyl-dihydrophenanthrene derivative, having a highly strained structure. The unique structure of 1, [α] d 21 + 168.2 ° (c 0.25, MeOH) possesses both planar and axial chirality. This is the first example of the isolation of such a compound from nature.

Total synthesis of cyclo-l-rhamnohexaose by a stereoselective thermal glycosylation

Abstract The first cyclooligosaccharide of L series, cyclo-L-rhamnohexaose, have been synthesized from L-rhamnose by α-selective thermal glycosylation and PhSeOTf promoted cycloglycosylation.

Steroidal Glycosides from the Fresh Stem of Stephanotis lutchuensis var.japonica (Asclepiadaceae). Chemical Structures of Stephanosides K-Q

The structural elucidation of seven related oxypregnane-oligoglycosides stephanosides K (1), L (2), M (3), N (4), O (5), P (6), and Q (7) from the fresh stem of Stephanotis lutchuensis var. japonica (Asclepiadaceae) was achieved through on a detailed study of their high-field 1H- and 13C-NMR spectra. The results show that all the sugars are beta (1-->4)-linked. The aglycones of stephanosides K, M, and O, and stephanosides L, N, and P were identified as 12-O-cinnamoyl-20-O-(E)-2-methyl-2-butenoyl, and 12-O-cinnamoyl-20-O-nicotinoyl derivatives of (20S)-pregn-6-ene-3 beta,5 alpha,8 beta,12 beta,14 beta,17 beta,20-heptaol, respectively. The aglycone of stephanoside Q was 12-O-cinnamoyldeacetylmetaplexigenin (kidjoranin).

Revisit to the sulfonation of pyrroles: is the sulfonation position correct?

Abstract Sulfonation of pyrrole and its 1-methyl derivatives with a sulfur trioxide–pyridine complex was found to give 3-sulfonated pyrroles, but not 2-sulfonates as described in textbooks. The replacement of 1-methyl-2-tri- n -butylstannylpyrrole with trimethylsilyl chlorosulfonate, followed by quenching with aq. NaHCO 3 also generated sodium 1-methylpyrrole-3-sulfonate, not 2-sulfonate.

Sesqui- and diterpenoids from Plagiochila species

Abstract Two new 2,3-secoaromadendrane-type sesquiterpenoids, plagiochiline N and acetoxyisoplagiochilide, and a new aromadendrane-type sesquiterpenoid, ent-4β,10α-dihydroxyaromadendrane, were isolated from the Japanese liverwort Plagiochila ovalifolia along with some previously known sesqui- and diterpenoids. A new pinguisane-type sesquiterpenoid, named dehydropinguisone was isolated from the New Zealand liverwort Plagiochila retrospectans . Their stereostructures have been determined by NMR techniques and X-ray crystallographic analysis. The chemosystematics of some Plagiochila species are discussed.