Kaoru Kuriyama

A disproof of Kahn-Hehre's proposal on the ground state conformations and the steric course of the Diels-Alder reaction of vinyl sulfoxides

Abstract X ray analysis and CD spectra of some optically active vinyl sulfoxides revealed that the conformation of vinyl sulfoxides is affected by the substituents at alpha or beta position. The results strongly support our previous suggestion that the most stable conformation ( s - trans or s - cis ) dictates the diastereoselectivity of the Diels-Alder reaction of vinyl sulfoxides.

Dimethyl (R)S-2-(10-isobornylsulfinyl)maleate, a chiral synthetic equivalent of dimethyl acetylenedicarboxylate: Preparation and its application to the formal chiral synthesis of (-)-neplanocin A and (-)-aristeromycin

Abstract A novel chiral synthetic equivalent of dimethyl acetylenedicarboxylate, dimethyl ( R )S-2-(10-isobornylsulfinyl)maleate (3), was synthesized. Diels-Alder reaction of (3) with cyclopentadiene proceeded with high stereo- and diastereo-selectivity to afford the cycloadduct (4) almost exclusively, which has been transformed into the half-ester (7), an intermediate in the synthesis of (-)-aristeromycin and (-)-neplanocin A.

Optical rotatory dispersion studies—CIII : Thiosteroids—XVI optical rotatory dispersion and circular dichroism of twisted sulphur-containing chromophoric systems☆☆☆

Abstract The optical properties of a number of di- and trithiocarbonates, oxathiolanes, dithiolanes and oxathianes, have been examined. Optical rotatory dispersion and circular dichroism measurements have demonstrated the optical activity of the various absorption bands in these compounds and such data serve to generate a chirality rule in which the sense of twist of the chromophoric ring corresponds in sign to the measurements in question.

A study on the interaction of ribonuclease St with guanosine 3′-monophosphate by circular dichroism

Abstract The interaction of ribonuclease St with guanosine 2′(3′)-monophosphate, a competitive inhibitor for the enzyme, has been studied by means of their circular dichroism spectra. Ribonuclease St exhibits a strong positive band at 234 mμ and a negative band at 280 mμ. Upon addition of the nucleotide to the enzyme, a significant change in the circular dichroism spectrum occurs in the 280 mμ region alone, and this has been used to characterize the interaction of nucleotide and enzyme. Mixing enzyme which had been inactivated by modification with iodoacetate with the nucleotide did not produce any change in the spectrum, though the circular dichroism spectra of the native and the modified enzyms, are virtually identical. The results are discussed together with the results obtained using bovine pancreatic ribonuclease and cytidine 2′(3′)-monophosphate.

Synthesis and chiroptical properties of bridged 2,2′-diaminobiphenyl derivatives

The relationship between c.d. spectra and the conformation of chiral 2,2′-diaminobiphenyls was investigated as a function of the torsion angle between the benzene ring planes. The molecular structures of (S)-(+)-4,5,6,7,11,12,13,14-octahydro[1]benzazocino[7,6,5-efg][1]benzazocine (22), (S)-(–)-2,2′-diamino-6,6′-dimethylbiphenyl (25), and (S)-(–)-(6R,7R)-5,6,7,8-tetrahydro-1,6,7,12-tetramethyldibenzo[e,g][1,4]diazocine (27) were determined by X-ray analysis. The shape of the c.d. spectrum of (22)(trans-conformation) is similar to those of (25) and (27)(cis-conformation). The experimental results and theoretical consideration by the exciton approximation and the π-SCF-MO approximation indicated that the shape of the c.d. spectrum is the same at least for torsion angles of 0–120°. On the other hand, the shape of the c.d. spectrum of the protonated species was inverted with a critical torsion angle of ca. 90°.

Diels-Alder reaction—IX : The reaction of 1,7-, 2,7-, 2,6-, and 1,6-dihydroxynaphthalene and 6-bromo-2-naphthol with maleic anhydride and the resolution of some derivatives of the adducts

Abstract The Diels-Alder reaction of 1,7-, 2,7-, 2,6-, 1,6-dihydroxynaphthalene and 6-bromo-2-naphthol with maleic anhydride was investigated. All of these 2-naphthol derivatives gave exo- and endo-adducts (II and III) except for the bromo-naphthol, from which only endo-adduct was obtained. The assignment of exo or endo configuration was based on lactone formation on NaBH4 reduction possible only from the exo isomer, comparison of NMR spectra and in some cases dipole moment measurements. The exo/endo ratios of the formed adducts vary over a wide range. Revolution of methoxy-trans-dicarboxylic acid VIII and IX was accomplished via the cinchonidine salts. The absolute configratuion of the resolved active compounds was determined by applying the octant rule.

Thiosteroids—18 (bible acids and steroids XXXIII) : Optical rotatory power of steroidal episulfides and oxathiolanes

Abstract An examination of the rotatory properties of a number of steroid episulfides and oxathiolanes leads to an important generalization, which is deduced from a semi-quantitative treatment of the n-σ transition. The sector rule relates the sign and amplitude of the Cotton effect exhibited by episulfides and oxathiolanes to the disposition of atoms in space about the sulfur atom.

Optical rotatory dispersion studies—CXII thiosteroids (20) : An octant rule for the thiocyanate chromophore and its application to rotameric equilibrium studies in the steroid series

Abstract Optical rotatory dispersion and circular dichroism measurements of a number of steroidal thiocyanates have demonstrated that a low intensity absorption near 250 nm is optically active. On the assumption that this transition of thiocyanates is qualitatively similar to the n → π * transition of azides, an octant rule is proposed for thiocyanates, which leads to the prediction of the sign of the Cotton effect. Its potential utility is demonstrated by analyzing rotameric contributions of various steroidal thiocyanates.

Synthesis and asymmetric Diels–Alder reaction of dimethyl (‘d-isoborneol-10-sulphinyl’)maleate: novel route to key intermediates for synthesis of some carbocyclic nucleosides and terpenoids

The chiral sulphoxide 1 was synthesized from 10-mercaptoisoborneol via diastereoselective oxidation. The dienophile 1 reacted with cyclopentadiene in the presence of a Lewis acid to give the adducts 7 and 8 with high diastereoselectivity (∼100%). Diels–Alder reaction of 1 in the absence of a Lewis acid afforded the adduct 9 as the major product with reversed diastereoselectivity. The adduct 7 was transformed into a useful precursor 11 for synthesis of carbocyclic nucleosides. The adducts 7 and 9 were converted into a bridged bicyclic lactone 21 in an enantiodivergent manner via selective reduction followed by reaction with samarium diiodide.

Quinones and related compounds in higher plants. Part 16. Naphthoquinones from Radermachera sinica Hemsl. (Bignoniaceae)

Five new naphthoquinones, along with the known naphthoquinones lapachol (1), dehydro-α-lapachone (2), and dehydroiso-α-lapachone (3), have been isolated from the wood of Radermachera sinica Hemsl. The structures of these new quinones were established as 3-hydroxy-6-methoxydehydroiso-α-lapachone (4), 3-hydroxydehydroiso-α-lapachone (5), 3,6-dimethoxydehydroiso-α-lapachone (6), 3,5-dihydroxy-6-methoxydehydroiso-α-lapachone (7), and 2-isopropenylnaphtho[2,3-b]furan-4,9-quinone (8). These quinones were found to be mixtures of both enantiomers in various proportions, e.g., (3), 2R:2S, 4.5:1; (4), 2R,3R:2S,3S, 1:1; (5), 2R,3R:2S,3S, 4.2:1; (6), predominantly 2R,3R; and (7), predominantly 2S,3S.