Carboxylation pathways, comparison

Comparison of CAM with Other Carboxylation Pathways in Plants... 

Other chemical studies did not find sex or seasonal differences in the composition of mammalian scents. No sex differences in the composition of mixtures of volatile compounds from glands have been found in the brushtailed possum, Trichosurus vulpecula, for example. The same profiles of low-molecular-weight branched carboxylic acids were found in paracloacal gland secretions of males and females (Woolhouse etal., 1994). Branched carboxylic acids also occurred in the preorbital gland secretion of a female sika deer [Ccrvus nippon) (Wood, 2004). Comparisons between the compositions of secretions in different, related species permit assumptions about functional adaptations and possible evolutionary pathways. Such comparisons are available for five Mustek species (Brinck etal., 1983), and three species of hyenas (Buglass etal., 1990). 

Allyldiethylamine behaves similarly, but the yields are low since neither the starting amine nor the products are stable to the reaction conditions. For the efficiency of the cyclopropanation of the allylic systems under discussion, a comparison can be made between the triplet-sensitized photochemical reaction and the process carried out in the presence of copper or rhodium catalysts whereas with allyl halides and allyl ethers, the transition metal catalyzed reaction often produces higher yields (especially if tetraacetatodirhodium is used), the photochemical variant is the method of choice for allyl sulfides. The catalysts react with allyl sulfides (and with allyl selenides and allylamines, for that matter) exclusively via the ylide pathway (see Section 1.2.1.2.4.2.6.3.3. and Houben-Weyl, Vol. E19b, pll30). It should also be noted that the purely thermal decomposition of dimethyl diazomalonate in allyl sulfides produces no cyclopropane, but only the ylide-derived product in high yield.Very few cyclopropanes have been synthesized by photolysis of other diazocarbonyl compounds than a-diazo esters and a-diazo ketones, although this should not be impossible in several cases (e.g. a-diazo aldehydes, a-diazocarboxamides). Irradiation of a-diazo-a-(4-nitrophenyl)acetic acid in a mixture of 2-methylbut-2-ene and methanol gave mainly l-(4-nitrophenyl)-2,2,3-trimethylcyclo-propane-1-carboxylic acid (19, 71%) in addition to some O-H insertion product (10%). ... 

In general, mechanisms for the biosynthesis of polyamides can be divided into three different pathways, which mainly differ in the mode of activation of the monomers (adenylation or phosphorylation), the dependency on a template, and the enzyme apparatus. In comparison to the activation by phosphorylation, adenylation involves synthesis of a phosphodiester bond between the hydroxyl group of the carboxylic group of the amino acid and the a-phosphate group of adenosine triphosphate (ATP). Activation by phosphorylation has been proposed that is, for synthesis of the tripeptide glutathione (Gly-Glu-Cys) or transpeptidase, the... 

The ko value of 11 mol" suggests that this pathway may involve an outer-sphere transfer by comparison with the acid-independent rate constant for (HghOsCo py + (0.241 mol s ) where such a mechanism is required owing to lack of a suitable bridging group. At low acidities, however, there is a substantial inner-sphere contribution, in which there is remote attack by the reductant at the carboxylic acid group with the formation of the dinuclear intermediate which is in steady-state equilibrium with the reactants. 

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