Yoshihiko Saito

Diterpenes from Euphorbia helioscopia

Abstract A number of diterpenes have been isolated from Euphorbia helioscopia and their stereostructures elucidated on the basis of the spectral data together with some chemical evidence. The absolute configuration of cuphoscopin A and euphornin in particular have been unambiguously determined by means of X-ray crystallographic analysis.

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 isolation and structures of euphoscopins a and b

Abstract Two new toxic substances, euphoscopins A and B, have been isolated from the plant Euphorbia helioscopia L., and their absolute stereostructures also been elucidated on the basis of their spectral data coupled with an X-ray crystallographic analysis of the p -bromobenzoate readily obtained on treatment of euphoscopin A with p -bromobenzoyl chloride - pyridine. These antitumor substances belong to a group of jatrophone-type diterpenes.

Structural and conformational studies on euphornin and related diterpenes

Abstract In addition to euphornin, three new toxic substances (euphornins A, B and C) have been isolated from the plant Euphorbia helioscopia L., and their absolute stereostructures also been elucidated on the basis of their spectral data and some chemical evidence together with an X-ray crystallographic analysis of the p-bromobenzoate derived from euphornin. Furthermore, their conformations have also been discussed.

Synthetic studies of rifamycins. VI. Preparation and elaboration of the aromatic segment for the synthesis of rifamycin W

Abstract A convenient preparation of the aromatic segment 3 starting from 3,5-dibromo-2,6-dimethoxytoluene 5 and furan was described along with the elaboration of 3 by the aldol coupling with the aliphatic segment 2 to the synthetic precursor 4 of rifamycin W.

The synthesis of a tricyclic hydroazulenone from exo-epoxygermacrene-Din connection with periplanone A

Abstract In connection with periplanone A, acid-catalyzed reaction of germacrene-D epoxide has been carried out using AlCl 3 in ether to afford a hydroazulene which has been further transformed into one of the hydroazulenones proposed to be periplanone A.

Electron-Density Distributions in Inorganic Compounds

Publisher Summary This chapter discusses the electron-density distributions in inorganic compounds. It comprises a survey of electron-density studies of inorganic compounds. The compounds included are transition metal complexes, minerals such as oxides, sulfides, and spinels, organometallic compounds, and metals. The measurement of electron density in inorganic compounds is a developing field. Molecular wave functions have conventionally been calculated to obtain molecular energy levels, but now they can be directly compared with the spatial distribution of electrons. Valence electron density, containing chemically important information, is relatively small compared to the total electron density. Electron-density changes due to molecular formation, i.e., charge migration and charge accumulation, are small in magnitude compared to the total electron density.

Total syntheses of isodihydrofutoquinol a, futoquinol, and isofutoquinol A and B

Summary Isodihydrofutoquinol A has been synthesized starting from 4-benzyloxy-2-methoxy-acetophenone, wherein the 2,5-cyclohexadienone moiety has been constructed efficiently by means of electrochemical method. Isodihydrofutoquinol A has been further converted into isofutoquinol A and B through futoquinol. In addition, the stereostructure of isofutoquinol A has been unambiguously determined on the basis of an X-ray crystallographic analysis.

Synthetic Approach Toward Antibiotic Tunicamycins, 4. X-Ray Crystal Structure Analysis of a Higher-Carbon Nitro Sugar

Abstract A higher-carbon carbohydrate, a derivative of undecose has been synthesized by the potassium fluoride-catalyzed addition of a nitro sugar to a sugar aldehyde. The addition of methyl 5-de-oxy-2,3-O-isopropylidene-5-nitro-β-D-ribofuranoside to methyl 2-benzyloxycarbonylamino-2-deoxy-3,4-O-isopropylidene-α-D-galacto-dialdopyranoside-(1, 5) yielded a single diastereomer of the nitro undecose derivative. The absolute configuration of two chiral centers of the derivative has been established by the X-ray crystal structure analysis.

Preparation and characterization of [MIII(SeCH2CH2NH2){N(CH2CH2NH2)3}]2+ (MIII = Co, Rh) and molecular structure of the perchlorate of the rhodium(III) complex

Abstract By reaction of [RhCl2(tren)]+ (tren = tris(2-aminoethyl)amine) with CH3SeCH2CH2NH2 in water in the presence of NaBH4, or in its absence in ethanol, only one of the two geometrical isomers of [Rh(SeCH2CH2NH2)(tren)]2+ was formed. Both of the two geometrical isomers of the corresponding CoIII complex were formed by the reaction of CoII-tren species with (NH2CH2CH2Se–)2. The structure of the RhIII complex was determined by the X-ray method. Crystal data [Rh(C2H6NSe)(C6H18N4)](ClO4)2, monoclinic, space group P21/c, a = 9.012(1), b = 14.438(1), c = 14.550(4) A, β = 104.81(1)°, and Z = 4. The final R value was 0.026. The complex ion has a distorted octahedral structure with cis(tertiary amine nitrogen, Se) configuration. The RhN bond length for the amine nitrogen bonded trans to the selenium atom is longer by 0.039(6) A than the average cis RhN distance for the two other primary amine nitrogen of the tren ligand, indicating rans influence of the selenium atom.