- Total synthesis of streptonigrone
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(Chemical Equation Presented) A total synthesis of streptonigrone, 1, is described, which incorporates a one-step synthesis of substituted pyridones devised in our laboratory. Other aspects of the synthesis that differentiate the present approach from previous ones are the use of a Conrad-Limpach reaction, rather than the customary Friedlaender methodology, to assemble the quinoline segment of 1, and the implementation of an anionic sequence for the functionalization of a key pyridone intermediate.
- Chan, Bryan K.,Ciufolini, Marco A.
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p. 8489 - 8495
(2008/02/13)
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- Cephalosporin compounds
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The present invention relates to new cephalosporin compounds of the formula(I), pharmaceutically acceptable non-toxic salts thereof, and physiologically hydrolyzable esters and solvates thereof, which have potent and broad antibacterial activities STR1 wherein R1 is a C1?4 alkyl, C3?4 alkenyl, C3?4 alkynyl group, or --C(Ra)(Rb)CO2 H1 wherein Ra and Rb are the same or different, and each is a hydrogen atom or a C1?4 alkyl group, or Ra and Rb form a C3?7 cycloalkyl group with the carbon atom to which they are linked; R2 is a C1?4 alkyl, C3?4 alkenyl or C3?4 cycloalkyl group, a substituted or unsubstituted amino group, or a substituted or unsubstituted phenyl group; R3 is hydrogen or a C1?4 alkyl group; and Q is N or CH. The invention further relates to a process for preparing said compounds, and to pharamaceutical compositions containing said compounds.
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- Isoxazoles. VII: Hydrolysis of 4-methyl-5-isoxazolylnaphthoquinone derivatives in aqueous solutions
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The kinetics for the degradation of 2-(4-methyl-5-isoxazolylamine)-N-(4-methyl-5-isoxazolyl)-1,4- naphthoquinone-4-imine (1) in solution were investigated at 70 °C and at a constant ionic strength of 0.5 over a pH range of 1.75 to 12.85. The degradation rates were determined by absorption and second-derivative UV spectrometry. Two degradation products were identified in acidic and neutral pHs; they are 4-N-(4-methyl-5-isoxazolyl)-1,2-naphthoquinone (2) and 2-methyl-cyanoacetamide (5), respectively. In alkaline pH, two degradation products, 2-hydroxy-N-(4-methyl-5-isoxazolyl)-1,4-naphthoquinone-4-imine (3) and 5-amino-4-methylisoxazole (4), were isolated. The pathway for degradation of 1 in acidic and neutral pH followed consecutive first-order kinetics since 2 undergoes hydrolysis giving 2-hydroxy-1,4-naphthoquinone (6) and 2-methylcyanoacetamide (5). No appreciable buffer effect on the degradation of 1 and 2 was observed for any of the buffer species in this study. The pH-rate profiles exhibited specific acid and specific basic catalysis for 1 and specific acid catalysis for 2. The maximum stability for 1 and 2 occurred in the neutral pH region.
- Longhi,De Bertorello,Brinon
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p. 573 - 577
(2007/10/02)
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- Resonanzstabilisierung von Alkylradikalen durch zwei geminale Cyangruppen
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Effects of Substituents on the Strength of C-C bonds, 10. - Resonance Stabilization of Alkyl Radicals by Two Geminal Cyano groups The activation parameters of the homolytic cleavage of the Cq-Cq bonds of several dialkylated malonodinitriles (2-5) and of 1,1,2,2-tetracyanoethane (7) and the heat of dissociation of 6 in solution have been determined.Together with the ground state strain of the radical precursor (obtained from the heats of combustion or EFF calculations) the steric influence on the dissociation process has been determined.The resonancestabilization energy of α,α'-dicyanoalkyl radicals then calculated was (12.4 +/- 0.9) kcal/mol.This result is discussed within the concept of capto-dative stabilization.The destabilizing interaction of two geminal cyano groups is apparently the same in the ground state of 2-7 and the radicals generated from them.
- Pakusch, Joachim,Beckhaus, Hans-Dieter,Ruechardt, Christoph
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p. 1191 - 1198
(2007/10/02)
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- Kinetic Evidence for the Intermediacy of 1-Azirines in the Gas-Phase Thermal Isomerization of 3H-Isoxazoles to α-Carbonylacetonitrile Derivatives
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Thermal isomerization of 5-methylisoxazole and 5-amino-4-methylisoxazole to acetylacetonitrile and 2-cyanopropionamide, respectively, was studied in a flow system.The activation parameters are reported.According to the experimental results, a concerted 1,3 sigmatropic shift to 1-azirines is proposed as the rate-limiting step in these reactions.A general reaction mechanism for the isomerization of isoxazoles into 1-azirines, oxazoles, and α-carbonylacetonitrile derivatives is discussed.
- Perez, Jorge D.,Yranzo, Gloria I.,Wunderlin, Daniel A.
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p. 982 - 984
(2007/10/02)
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