Dynamics of photodissociation of 3,3,3-d(3)-propene at 157 nm: site effect and hydrogen migration

In a preceding paper [Lee et al., J. Chem. Phys. 119, 827 (2003)], we measured the kinetic-energy distributions P(E(t)) and branching ratios of products from photolysis of propene at 157 nm using time-of-flight spectroscopy combined with photoionization. In the present work, hydrogen migration before fragmentation and a site effect on P(E(t)) and branching ratios were revealed from the photodissociation of CD(3)CHCH(2). Labeling of the methyl group with deuterium enabled us to differentiate between elimination of atomic and molecular hydrogen from the vinyl moiety and from the methyl moiety; the P(E(t)) and relative yields for the formation of H, D, H(2), HD, and D(2) were measured. Deuterium labeling allowed us to also differentiate the fragmentation after hydrogen transfer from that before hydrogen migration. The observation of isotopic variants of CD(3) and C(2)H(3) radicals in the C-C bond cleavage provides evidence for hydrogen transfer of propene because of site specificity. The fraction of fragmentation after hydrogen transfer is estimated to be 25%. The isotope-specific branching ratios for five dissociation pathways of CD(3)CHCH(2) were evaluated.     

Synthesis of 4-acetylisocoumarin: first total syntheses of AGI-7 and sescandelin

A practical synthetic route to 4-acetylisocoumarins and the first total synthesis of AGI-7 (5) and sescandelin (4) are described. The readily available homophthalate 8 was transformed to the vinylogous amide ester 13 in high overall yield. Upon treatment of 13 with refluxing aqueous formic acid, the desired 4-acetylisocoumarin (5) and its regioisomer 3-methyl-4-formylisocoumarin (17) were produced in a 3:1 ratio. After separation of the desired product (5) from the unwanted minor isomer, the enantioselective reduction of AGI-7 by borane in the presence of Corey's (S)-oxazaborolidine reagent afforded (+)-sescandelin (4) with a 93% ee.     

Isolation of essential oils from tobacco by gas co-distillation/solvent extraction

Summary The essential oils have been isolated from tobacco leaves using a simple gas co-distillation apparatus. The method involves co-distillation with water under the continuous stream of an inert gas with subsequent single solvent extraction of the distillate. The extract is analysed on GC and GC/MS in splitless injection mode without further concentration. The method was evaluated for reproducibility using n-octadecane as an internal standard. The distillation-extraction procedure was reporducible with an average deviation of ±3% for the major constituents. The present method was applied to the analyses of the essential oils of other agricultural products.Dedicated to Dr. L. S. Ettre on the occasion of his 60th birthday.     

Comparison of gas chromatographic and high-performance liquid chromatographic assays for the determination of debrisoquine and its 4-hydroxy metabolite in human fluids

A comparison of an established gas chromatographic assay for 4-hydroxydebrisoquine and debrisoquine and a modified high-performance liquid chromatographic assay was made. Both assays used guanoxan as the internal standard and required derivatization of all three compounds with acetylacetone at 96 degrees C for 2.5 h and subsequent ethereal extraction and cleaning steps before chromatographic analysis. For detailed pharmacokinetic studies the gas chromatographic assay was more sensitive in the measurement of low concentrations in plasma, but the liquid chromatographic assay was adequate for phenotyping the 4-hydroxylation of debrisoquine in a population. In the latter assay a mobile phase consisting of 70% methanol in water at pH 3.5 (adjusted with orthophosphoric acid containing 10 mM 1-pentanesulphonic acid was employed (flow-rate 1.5 ml/min) with a pre-column (C8) linked to a reversed-phase muBondapak C18 cartridge in a Z-module. The eluate was detected at 248 nm. With this assay it was observed that the buccal absorption of debrisoquine and 4-hydroxy-debrisoquine was affected by the pH of the buccal medium. This indicates that urinary pH may influence the excretion of both substances at high pH. The debrisoquine-to-4-hydroxydebrisoquine ratio may be dose-dependent.