T.T Nakashima

Simulation of two-dimensional NMR spectra using product operators in the spherical basis

Abstract The product operator description of magnetic resonance experiments is developed in the spherical-tensor basis, and a computer simulation scheme, employing this description, is reported. The utility of simulations in the design of selective phase cycles and in the study of the effects of spectrometer imperfections is demonstrated.

Selective 2D DEPT heteronuclear shift correlation spectroscopy

Abstract Selective 2D DEPT heteronuclear shift correlation maps for cholesterol in CDCl 3 are reported and demonstrate the selectivity and utility of these experiments. Improvements in the basic 2D DEPT sequence to effect quadrature detection and proton-proton decoupling in the f 1 domain are reported. An implementation in which the 2D data files for proton flip angles τ = 30, 90, and 150° are acquired and used to construct selective CH, CH 2 , and CH 3 maps is shown to be twice as efficient as the previous implementation where separate experiments were performed to construct each selective 2D map.

Synthesis of 1,2,4-tri-O-acetyl-3,6-di-O-benzyl-5-deoxy-5-C-[(S)-phenylphosphinyl]-β-d-glucopyranose: The first gluco type of hexopyranose derivative having phosphorus in the hemiacetal ring

Abstract Oxidation of 3,6-di- O -benzyl-1,2- O -isopropylidene-α- d -glucofuranose with pyridinium chlorochromate in the presence of molecular sieves, followed by conversion into the p -tolylsulfonylhydrazone, addition of methyl phenylphosphinate, and reduction with sodium borohydride, provided the key intermediate, namely, 5( R , S )-3,6-di- O -benzyl-5-deoxy-1,2- O -isopropylidene-5- C -[(methoxy)phenylphosphinyl]-α- d - xylo -hexofuranose, in 23% overall yield. Treatment of this compound with sodium dihydrobis(2-methoxyethoxy)aluminate, followed by the action of mineral acid and acetic anhydride, yielded the crystalline title compound, the structure of which was established on the basis of mass and 400-MHz, 1 H-n.m.r. spectra. A general dependence of 2 J PH values on the OPCH dihedral angles effectively served for assigning the configuration of C-1, C-5, and the ring-phosphorus atom of the present product and other such 5- C -phosphinylhexopyranoses.

Synthesis of 4,5-dideoxy-4-C-[(R,S)-phenylphosphinyl]-d-ribo- and l-lyxo-furanose and their 1,2,3-triacetates

Abstract 2,3- O -Isopropylidene- d -ribose diethyl dithioacetal, prepared from d -ribose, was converted in three steps into the corresponding dimethyl acetal, which was monotosylated at O-5, and the ester oxidized at C-4 with pyridinium chlorochromate; addition of methyl phenylphosphinate to the resulting pentos-4-ulose derivative then provided (4 R,S )-4,5-anhydro-2,3- O -isopropylidene-4- C -[( R,S )-(methoxy)phenylphosphinyl]- d - erythro -pentose dimethyl acetal. Hydrogenation of this compound in the presence of Raney Ni, followed by reduction with SDMA, hydrolysis, and acetylation, yielded the title compounds (seven kinds), the structures of which were established on the basis of their 400-MHz, 1 H-n.m.r. and mass spectra. A general dependence of the 2 J PH and 3 J PH values on the OPCH and PCCH dihedral angles provided an effective method for the assignment of the configurations and conformations of these 4-deoxy-4-phosphinyl-pentofuranoses.

Synthesis of 1,2,4-tri-O-acetyl-5-deoxy-5-C-[(R and S)-methoxy-phosphinyl]-3-O-methyl-α- and -β-d-xylopyranose, and their structural analysis by 400-MHz, proton nuclear magnetic resonance spectroscopy

Abstract 5-Deoxy-5-iodo-1,2- O -isopropylidene-3- O -methyl-α- d -xylofuranose, prepared quantitatively from its 5- O p -tolylsulfonyl precursor, readily gave the 5- C -(diethoxy-phosphinyl) derivative. Treatment of this compound with sodium dihydrobis(2-methoxyethoxy)aluminate, followed by hydrogen peroxide, mineral acid, and hydrogen peroxide, yielded 5-deoxy-5- C -(hydroxyphosphinyl)-3- O -methyl-α,β- d -xylopyranoses in 65% overall yield. The structures of these sugar analogs were effectively established on the basis of the mass and 400-MHz, 1 H-n.m.r. spectra of the four title compounds, derived by treatment with diazomethane and then acetic anhydride in pyridine. 5- C -[( S )-(1-Acetoxyethenyl)phosphino]-1,2,4-tri- O -acetyl-5-deoxy-3- O -methyl-β- d -xylopyranose was also isolated and characterized.

Improvement of INADEQUATE using compensated delays and pulses

Abstract A J -compensated homonuclear spin-echo sequence is developed from the 90 α o 180 α+2π/3 o composite pulse using a product-operator analogy between homonuclear spin-spin coupling and RF pulses, and a J -compensated INADEQUATE sequence is constructed using this spin-echo sequence. Detailed study of the efficiencies of various composite pulses in minimizing resonance-offset effects in INADEQUATE experiments showed that five-step symmetric phase-altemating composite pulses are most effective. The sequences C-INADEQUATE, which incorporates composite pulses, and JC-INADEQUATE, which includes both offset and J -compensation, are shown to have a sensitivity significantly higher than that of conventional INADEQUATE.

Experimental and theoretical investigation of 2D-13C DEPT spectra on CDn systems☆

Abstract Coupled 2 D- 13 C DEPT spectra for the CD, CD2, and CD3 systems are reported and a thorough analysis of these experiments using the density matrix theory is presented. DEPT is shown to be useful for selective enhancement of 13 C resonances from CD fragments, but less practical for the selective enhancement of resonances from CD 2 and CD 3 groups.

A simple method for the determination of the deuterium decoupler pulse angle

Abstract A simple 90°c-τ-θ-D pulse sequence is demonstrated to provide a convenient method for calibration of the decoupler (deuterium) pulse lengths in 13CD NMR experiments. Experimental and theoretical studies of the π and θ dependence of the 13C spectra for CD, CD2, and CD3 systems are reported.

Edited heteronuclear relay experiments

Abstract Methods for the CHn editing of HOHAHA relay maps using DEPT and techniques for the suppression of directly bonded correlations have been developed. The complexity of HOHAHA relay maps can be reduced significantly and ambiguities due to overlap may be eliminated using these methods. A new broadband “purge” sequence was found to be most effective in suppressing directly bonded correlations.

Compensated APT pulse sequences

In this Communication, we focus on the behavior of transverse carbon magnetizations for 13 CH, 13 CH 2 and 13 CH 3 fragments during APT-like sequences. Two J-compensated spin-echo experiments related to the spin-flip experiment are described and their relative merits evaluated