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51.
Summary The simultaneous stereospecific assay of four stereoisomers of diltiazem hydrochloride in bulk drug and aqueous solution was
developed using HPLC on a Chiralcel OF column. The four isomers were quantitated with good precision by the internal standard
method. The chiral inversion of (+)-cis-diltiazem hydrochloride in vitro, stability of its (2S, 3S) configuration in the solid
and aqueous states was examined by HPLC. Chiral inversion of (+)-cis-diltiazem hydrochloride was not observed in the solid
state, and its (2S, 3S) configuration was stable to heat, humidity and light. Chiral inversion of (+)-cis-diltiazem hydrochloride
(2S, 3S) was observed in aqueous solution under UV, but not in aqueous solution stored at 80°C for 5h nor under visible light
for 10 h. The (+)-cis-diltiazem hydrochloride (2S, 3S) epimerized to (+)-trans-diltiazem hydrochloride (2R, 3S) with a half-life
of 5h in aqueous solution under UV but the reverse chiral inversion of (+)-trans-diltiazem hydrochloride (2R, 3S) to (+)-cis-diltiazem
hydrochloride (2S, 3S) was not observed. 相似文献
52.
Enantiomerically pure iridium complexes with phosphino‐ and (phosphinooxy)‐substituted N‐heterocyclic carbene (NHC) ligands were synthesized. Investigation of their electronic properties showed a similar trans influence of the phosphino (or phosphinooxy) and the NHC units. The complexes were tested in iridium‐catalyzed hydrogenation. While low conversions were observed with unfunctionalized olefins, the catalysts proved to be suitable for hydrogenation of the α,β‐unsaturated ester 20 , allylic alcohol 21 , and imine 22 . The enantioselectivities were, however, moderate. 相似文献
53.
由手性配体α-D-葡萄糖衍生物5,6,7以及薄荷醇(8)和葑醇(9),经 Ulmann偶联反应得到光学活性的(R)-和(S)-6,6′-二硝基联苯-2,2′- 二甲酸(4a),(R)-6,6′-二甲基联苯-2,2′-二甲酸(4b),(R)-1,1′-联萘-2 ,2′-二甲酸(13)。以三个手性膦酰胺16,17,18和CuCl组成的手性络合物为 催化剂,通过2-萘酚直接氧化偶联得到(S)-2,2′-联萘酚(15)。产物4, 13,15具有中等ee值的光学活性。 相似文献
54.
Summary Direct separations of the enantiomers of cetirizine and related compounds have been achieved by reversed-phase HPLC on the
Chiralcel OD-R, a polysaccharide-derived chiral stationary phase; the mobile phase was usually perchlorate solution supplemented
with acetonitrile. Resolution of the enantiomers of cetirizine and related compounds was good. The effect of the acetonitrile
content of the mobile phase was investigated, and the effect of the structure of the chiral compounds on their behavior on
the Chiralcel OD-R column is discussed. 相似文献
55.
Summary The enantioseparation of amphetamine, methamphetamine and various ring-substituted amphetamines by use of a chiral stationary phase carrying immobilized native -cyclodextrin (-CyD) selectors is reported. The system is evaluated for resolving the specified compounds directly without any derivatization and after derivatization with phenyl isothiocyanate (PITC), naphthyl isothiocyanate (NITC) and 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC). This direct enantioseparation is compared with the features of indirect separation of diasteromeric derivatives after reaction with the optically pure Marfey's reagent employing a simple non-chiral alkyl-silica (RP-8) column. A selection of those methods best suited for each single amphetamine is given.Seventeen different samples of amphetamine, confiscated by the Swedisch police, were analyzed with respect to their enantiomeric composition. Within this set of samples synthesized by the same method no significant deviation from a racemic ratio could be observed. 相似文献
56.
We present a systematic procedure for the optimization of the expansion basis for the limited expansion of diatomic overlap density functional theory (LEDO-DFT) and report on optimized auxiliary orbitals for the Ahlrichs split valence plus polarization basis set (SVP) for the elements H, Li--F, and Na--Cl. A new method to deal with near-linear dependences in the LEDO expansion basis is introduced, which greatly reduces the computational effort of LEDO-DFT calculations. Numerical results for a test set of small molecules demonstrate the accuracy of electronic energies, structural parameters, dipole moments, and harmonic frequencies. For larger molecular systems the numerical errors introduced by the LEDO approximation can lead to an uncontrollable behavior of the self-consistent field (SCF) process. A projection technique suggested by L?wdin is presented in the framework of LEDO-DFT, which guarantees for SCF convergence. Numerical results on some critical test molecules suggest the general applicability of the auxiliary orbitals presented in combination with this projection technique. Timing results indicate that LEDO-DFT is competitive with conventional density fitting methods. 相似文献
57.
58.
59.
The enantiomers of some amino acids have been separated on commercial chiral TLC plates in reversed-phase mode. The effect
of the pH* of the aqueous-organic mobile phase on the retention and mobility of the enantiomers and on selectivity was investigated.
It was shown that for most of the amino acids investigated the highest enantioselectivity was obtained at pH* 3–4 or 6–7.
The drift and disturbance of the baseline on the chromatograms were also much smaller at pH* 3–4 and 6–7. 相似文献
60.
Raffaello Lazzaroni Roberta Settambolo Giuditta Guazzelli 《Journal of organometallic chemistry》2007,692(9):1812-1816
We review our recent results on the rhodium-catalyzed hydroformylation of chiral and prochiral N-allylpyrroles as a synthetic route to stereodefined 5,6-dihydro- and 5,6,7,8-tetrahydroindolizines. The indolizine nucleus at different degrees of unsaturation is a building block of natural and synthetic target compounds; thus new approaches, especially if stereoselective and/or stereospecific, are highly desirable. The construction of the indolizine architectures reported here occurs by formation of a C8-C9 bond through intramolecular cyclization of the 4-pyrrolylbutanal intermediate. 相似文献