Carbon skeleton determination

Stuermer, D. H. and Harvey, G. R. (1977a). Structural studies on marine humus A new reduction sequence for carbon skeleton determination. Mar. Chem. 5, 55-70. 

So far, we have focused our discussion on the relative nucleophilicities of natural nucleophiles. Let us now consider how certain structural features of the organic molecule (i.e., type of leaving group, type of carbon skeleton) determine the kinetics of nucleophilic substitution. In Table 3, the (neutral) hydrolysis half-lives are given for various monohalogenated compounds at 25°C. Also indicated are the postulated reaction mechanisms with which these compounds undergo SN reactions. As can be seen from Table 3, the carbon-bromide and carbon-iodine bonds hydrolyze fastest, about one to two orders of magnitude... 

Brownlee, R. G., and R. M. Silverstein A micro-preparative gas chromatograph and a modified carbon skeleton determinator. Anal. Chem. 40, 2077—2079 (1968). 

The degradation of 2,6-xylenol (2,6-dimethylphenol) by bacteria produces a metabolite with elemental composition C8///0O2 as determined by high-resolution mass spectrometry Which carbon skeleton and which relative configuration are deducible from the NMR experiments 44, all obtained from one 1.5 mg sample ... 

Determine the anticipated location in pyruvate of labeled carbons if glucose molecules labeled (in separate experiments) with " C at each position of the carbon skeleton proceed through the glycolytic pathway. 

Abscisin II is a plant hormone which accelerates (in interaction with other factors) the abscission of young fruit of cotton. It can accelerate leaf senescence and abscission, inhibit flowering, and induce dormancy. It has no activity as an auxin or a gibberellin but counteracts the action of these hormones. Abscisin II was isolated from the acid fraction of an acetone extract by chromatographic procedures guided by an abscission bioassay. Its structure was determined from elemental analysis, mass spectrum, and infrared, ultraviolet, and nuclear magnetic resonance spectra. Comparisons of these with relevant spectra of isophorone and sorbic acid derivatives confirmed that abscisin II is 3-methyl-5-(1-hydroxy-4-oxo-2, 6, 6-trimethyl-2-cyclohexen-l-yl)-c s, trans-2, 4-pen-tadienoic acid. This carbon skeleton is shown to be unique among the known sesquiterpenes. 

The 2D INADEQUATE spectrum and C-NMR data of 7-hydroxyfrulla-nolide are given. Determine the carbon-carbon connectivities, and subsequently build the entire carbon skeleton based on the 2D INADEQUATE experiment. 

Butadiene exists in two equilibrium structural isomers. They are represented in Fig. 7. However, with the usual Hflckel approximation these two structures cannot be distinguished, as interactions between nonadjaeent atoms have been neglected. Thus for either isomer, or even a hypothetical structure in which the carbon skeleton is linear, the secular determinant is the same, namelv. 

The distribution of formal charges in the carbon skeleton is determined by the functional groups (or heteroatoms) present on it. In this context is very useful to use the "Lapworth model" of alternating polarities. 

The name alkaloid comes from the fact that a number of NPs were formd in the nineteenth century which were alkaline. These chemicals were shown to contain a nitrogen molecule, and when their structures were determined it was formd that the nitrogen was usually in a heterocyclic ring (a cyclic carbon skeleton with one or more nitrogen atoms in the ring—see Figure 3.9). The N is usually protonated at physiological pH, thus many of these molecules are polar and hence water soluble. 

The multiple cleavage modes in ketones sometimes make difficult the determination of the carbon chain configuration. Reduction of the carbonyl group to a methylene group yields the corresponding hydrocarbon whose fragmentation pattern leads to the carbon skeleton. 

Homocysteine (Hey) metabolism is closely linked to that of the essential amino acid methionine and thus plays a central role in several vital biological processes. Methionine itself is needed for protein synthesis and donates methyl groups for the synthesis of a broad range of vital methylated compounds. It is also a main source of sulphur and acts as the precursor for several other sulphur-containing amino acids such as cystathionine, cysteine and taurine. In addition, it donates the carbon skeleton for polyamine synthesis [1,2]. Hey is also important in the metabolism of folate and in the breakdown of choline. Hey levels are determined by its synthesis from methionine, which involves several enzymes, its remethylation to methionine and its breakdown by trans-sulphuration. 

The first sesquiterpene thiocyanate to be isolated from a marine sponge was (15, 45, 65, 7/ )-4-thiocyanato-9-cadinene (253) from Trachyopsis aplysinoides. The structures of this compound and of an isothiocyanate with a new carbon skeleton (254), were determined by X-ray analysis and two additional isothiocyanates (255-256) were identified [258]. Isothiocyanate 254 was synthesised using an oxidative radical cyclisation reaction as a key step [259]. 

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