摘要:

AbstractA brief overview of the medicinal chemistry of the camptothecin family of antitumor agents is followed by a summary of a new synthetic approach to this class of compounds. This approach features a new 4 + 1 radical annulation.

ISSN:0009-4536    

DOI:10.1002/jccs.199300001

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractIn polycyclic conjugated hydrocarbons the Hückel (4n + 2)‐rule may be violated, so that certain (4n + 2)‐membcred rings cause thermodynamic destabilization. The structural conditions for the occurrence of such an effect are analyze d. Eight examples (of which seven are new) of non‐b enzenoid hydrocarbons are put forward, in which the Hückel rule is di

ISSN:0009-4536    

DOI:10.1002/jccs.199300002

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe two‐root (i,j,k) generalized Padé approximation (GPA) and three‐root (i,j,k,l) GPA as well as the two‐root continued fraction approximation (CFA) and the three‐root CFA are applied to the model of a three‐state avoided crossing. These two procedures for analytic continuation are compared. The results indicate that both methods provide good continuation into the complex plane and can be applied to locate the complex branch point. When the same input data are chosen, the GPA works slightly better than the CFA. According to our analysis, the two‐root procedure can be applied to locate the branch point around each region of avoided crossing in the problem of a multi‐state avoided crossing. The accuracy of the result is found to be associated the location of comple

ISSN:0009-4536    

DOI:10.1002/jccs.199300003

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractUsing ethylcellulose and cellulose triacetate as co‐wall materials, sustained release microcapsules of theophylline were prepared. The solid drug dispersed in the cellulose triacetate matrices was first prepared by solvent evaporation; then the matrices were microencapsulated by means of coacervation‐phase separation of ethylcellulose from toluene solution on addition of petroleum ether.The shapes and surface characteristics of theophylline, matrices and microcapsules were examined with a scanning‐electron microscope. The release of theophylline from various particles into distilled water was studied. The microcapsules had good characteristics of sustained release. The period for theophylline to dissolve from ethylcellulose microcapsules containing cellulose triacetate matrices was larger than those from only ethylcellulose microcapsules with a similar ratio of core to wall. The half‐time increased with increasing content of cellulose triacetate. The release pattern which was analogous to that from only ethylcellulose microcapsules obeyed a first‐order

ISSN:0009-4536    

DOI:10.1002/jccs.199300004

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractIon pairs formed from suitable cationic dye and anionic surfactant in water were separated by solvent extraction. The extracts were used subsequently for spectrophotometric determinations. The extraction of ion pairs with various combinations is described. Of the dyes and solvents examined, ethyl violet andp‐xylene are the most useful combination as the cationic dye and extraction solvent. The extracts are determined spectrophotometrically at 611.5 nm; the molar absorptivity is 1, 01 × 105M−1cm−1. The detection limit is 1.4 ppb in water. The method is simple, rapid and sensitive. It can also be applied to the determination of anionic surfactants in sea

ISSN:0009-4536    

DOI:10.1002/jccs.199300005

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractAfter human urine or serum was diluted (1 + 9) with HNO3(0.2%, v/v) and standard additions of Se solution (100 μ L−1), the diluted sample (10 μL) was introduced into the graphite cuvette. The matrix modifier [10μL, containing Pd (0.6 μg) + Ni (25 μg) + NH4NO3(80 μg) in HNO3(0.2%, v/v) for urine, or Pd (0.3 μg) + Ni (30 μg) + NH4NO3(80 μg) + Triton X‐100 (0.04%) in HNO3(0.2%, v/v) for serum, respectively] was added and the mixture was heated according to a temperature program. The matrix modifier containing NH4NO3in a suitable amount and a small amount of Pd enhanced the sensitivity for Se. The method detection limits (3σ) after dilution were about 4.9 ± 0.8 and 2.36 ± 0.18 μg L−1for urine and serum, respectively. The accuracy of this method was tested with SRM #2670 human urine Se and Seronorm Trace Elements #116 human serum Se, respectively, and the results of 97.6 – 101% and 100 – 104% were obtained with precision ± 0.3% and ± 2%, respectively. This method can be applied easily and accurately to the determination of concentration of total Se

ISSN:0009-4536    

DOI:10.1002/jccs.199300006

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractDirect reaction of iron pentacarbonyl with 1‐N,N‐disubstituted‐cyclohexa‐2,5‐dicnecarboxamide and 1‐N,N‐disubstituted‐cyclohexa‐1,3‐dienecarboxamide mixture (in which the disubstkuted group is diethyl or diphenyl) gave the isomeric tricarbonyl iron complexes of 2‐N,N‐disubstituted‐1,4‐η‐cyclohexa‐1,3‐dienccarboxamide (1), 1‐N,N‐disubslituted‐1,4‐η‐cyclohexa‐1,3‐dienecarboxamide (2), and5‐N,N‐disubstituted‐1,4‐η‐cyclohexa‐1,3‐dienecarboxamide (3) and tricarbonyliron complexes of l‐N,N‐disubstituted‐cyclohexenecarboxamide (4). These complexes were separated and characterized by IR, UV‐VIS,1H NMR, elemental analysis, and mass spectra. Only 1 isomerized to give 2 under acidic conditions; both 1 and 2 undergo hydride abstraction with triphenylmethyl hexafluorophosphatc. Complexes 3, undergo neither isomcrization nor hydride abstraction. According to the spectral data, the possible interaction between carboxamide and iron carbonyl moiety was investigated. T

ISSN:0009-4536    

DOI:10.1002/jccs.199300007

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe 1,2‐diphcnylethyl radical and derivatives were generated from photolysis of tran‐f‐stilbene and its derivatives 1–13 with secondary amines as quenchers. The 1,2‐diphenylelhyl radicals that escaped from the solvent cage were trapped by 2‐methyl‐2‐nitrosopropane (MNP) and were detected by the HPLCEPR method. The yield of the spin adduct is greater for tertiary amines. The smaller yields of the spin adduct formed from secondary amines are ascribed to greater reactivities of the 1,2‐diphenylethyl and dialkylamino radicals within

ISSN:0009-4536    

DOI:10.1002/jccs.199300008

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractSulfur‐substituted azido dienes1and11, conveniently prepared from the corresponding 3‐sulfolenes5and10, were thermolyzed to give pyrrolizidine and indolizidine products,6,7an

ISSN:0009-4536    

DOI:10.1002/jccs.199300009

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractRegioselective cycloaddition of (dimethylvinylidene)carbene (1) into aryl alkenes in the presence of other olefins is reported. The reaction is presumably controlled by the phenyl group, which forms an aromatic π‐complex with the carbene C‐3 orbital, followed by the selective addition of 1 to the closest phenyl‐substituted double bond. Also, this selectivity is assumed to be attributed to delocalization of aromatic π electrons which increases the electron density of the conjugated carbon‐carbon double bond, thus leading to the facile addition of vinylide

ISSN:0009-4536    

DOI:10.1002/jccs.199300010

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY