Diterpene glycosides from Stevia rebaudiana

Three novel diterpene glycosides were isolated for the first time from the commercial extract of the leaves of Stevia rebaudiana, along with several known steviol glycosides, namely stevioside, rebaudiosides A-F, rubusoside and dulcoside A. The new compounds were identified as 13-[(2-O-β-D-glucopyranosyl-3-O-β-D-glucopyranosyl-β-D-glucopyranosyl)oxy] ent-kaur-15-en-19-oic acid, 13-[(2-O-β-D-glucopyranosyl-3-O-β-D-glucopyranosyl-β-D-glucopyranosyl)oxy]-16β-hydroxy-ent-kauran-19-oic acid and 13-methyl-16-oxo-17-nor-ent-kauran-19-oic acid-β-D-glucopyranosyl ester on the basis of extensive 2D NMR and MS spectroscopic data as well as chemical studies.     

Transfer measurements for the Ti+Ni systems at near barrier energies

Large enhancements have been observed in the sub-barrier fusion cross sections for Ti+Ni systems in our previous studies. Coupled channel calculations incorporating couplings to 2⁺ and 3⁻ states failed to explain these enhancements completely. A possibilty of transfer channels contributing to the residual enhancements had been suggested. In order to investigate the role of relevant transfer channels, measurements of one- and two-nucleon transfer were carried out for ^46,48Ti+⁶¹Ni systems. The present paper gives the results of these studies.     

Determination of arsenic in refractory metals by radio-chemical charged-particle activation analysis

Arsenic is determined in tantalum and tungsten matrices via ⁷⁵As(p, n)⁷⁵Se and ⁷⁵As(d, 2n)⁷⁵Se reactions. Two ion-exchange procedures, with Dowex-1 columns, are described for the separation of the indicator radionuclides. Data on thick target yields for the ⁷⁵As(p, n)⁷⁵Se reaction are given. With 13-MeV proton or 15-MeV deuteron irradiation for 2 h at a current of 5 μA, the detection limit for arsenic is at the 10 μg kg^-1 level.     

Fluorine determination in different types of ivory by PIGE technique

Fluorine was determined by particle induced gamma-ray emission (PIGE) technique with 2.3 MeV protons in elephant, mammoth, aquatic (walrus, pot whale, narwhal, hippopotamus) and archaeological ivory, with concentration varying between 55 ppm and 2.3 %. The characteristic variation of F concentration with species shows that it has the potential to serve as a marker in identifying different types of ivory. Additionally, Na concentration was also reported in all the analysed samples.     

Cucurbitane Glycosides from Siraitia grosvenorii

Systematic phytochemical studies of the extract of Luo Han Go (Siraitia grosvenorii) furnished six known cucurbitane glycosides, namely, mogrosides IVa, mogrosides V and VI, isomogroside V, 11-oxomogroside V, and siamenoside I. The structures of all the isolated compounds were characterized on the basis of extensive spectral and chemical studies. Though the partial NMR spectral data has been reported for some of the isolated compounds previously, the complete ¹H and ¹³C NMR spectral assignments of all the isolated compounds are reported herewith for the first time based on COSY, HSQC, HMBC, and NOESY spectroscopic data.     

New pentacyclic polyketide dimeric peroxides from a Taiwanese marine sponge Petrosia elastica

Two novel pentacyclic polyketide dimers, dihalenaquinolides A (1) and B (2), have been isolated from the marine sponge Petrosia elastica collected in Nan-wan, Taiwan. The structures 1 and 2 were established on the basis of extensive spectral analysis.     

Catalytic asymmetric syntheses of tyrosine surrogates

Amino acid esters 5-11 as tyrosine mimics have been synthesized in excellent enantioselectivity (up to 99.6% ee) and in good overall chemical yields. The key step in the sequence was the Burk's [Rh(COD)(2R,5R)-Et-DuPhos]BF4-catalyzed asymmetric hydrogenation of enamides with a variety of reactive functional groups.     

A new diterpene glycoside from Stevia rebaudiana

From the commercial extract of the leaves of Stevia rebaudiana, a new diterpene glycoside was isolated besides the known steviol glycosides including stevioside, rebaudiosides A-F, rubusoside and dulcoside A. The new compound was identified as 13-[(2-O-β-D-glucopyranosyl-3-O-β-D-glucopyranosyl-β-D-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid-(2-O-α-L-rhamnopyranosyl-β-D-glucopyranosyl) ester (1) on the basis of extensive spectroscopic (NMR and MS) and chemical studies.     

Synthesis and Sensory Evaluation of <em>ent</em>-Kaurane Diterpene Glycosides

Catalytic hydrogenation of the three ent-kaurane diterpene glycosides isolated from Stevia rebaudiana, namely rubusoside, stevioside, and rebaudioside-A has been carried out using Pd(OH)₂ and their corresponding dihydro derivatives have been isolated as the products. Synthesis of reduced steviol glycosides was performed using straightforward chemistry and their structures were characterized on the basis of 1D and 2D NMR spectral data and chemical studies. Also, we report herewith the sensory evaluation of all the reduced compounds against their corresponding original steviol glycosides and sucrose for the sweetness property of these molecules.