Scission products

Both side-chain and main-chain scission products are observed when polyacrylates are irradiated with gamma radiation (60). The nature of the alkyl side group affects the observed ratio of these two processes (61,62). 

The two alkaloids which have been most completely investigated are quinine and cinchonine. The scission products of both fall into two classes, viz., derivatives of quinoline and derivatives of a second heterocyclic ring system, formerly referred to as the second half of the... 

It has already been shown that both the laevorotatory and dextrorotatory cinchona alkaloids on degradation yield scission products from the quinuclidine nucleus, which are structurally and optically identical, for example, meroquinenine, [a] -f- 27 6° d-/3-cincholoiponic acid. 

To these alkaloids Asahina and Mayeda assigned formulae, based on the reactions described, and on the first assumption, referred to above, that 2- -aminoethylindole was the scission product of evodiamine. Kermack, Perkin and Robinson pointed out that the evidence did not exclude the possibility that the base produced was in reality 3-)3-amino-ethylindole, in which case evodiamine and rutascarpine could be represented by the following formulas, which would bring them into line with harmine. 

These formulae explain the scission products of the two alkaloids and the conversion of evodiamine into rutaecarpine, and were accepted by Asahina. A partial synthesis of rutaecarpine was effected by Asahina, Irie and Ohta, who prepared the o-nitrobenzoyl derivative of 3-)3-amino-ethylindole-2-carboxylic acid, and reduced this to the corresponding amine (partial formula I), which on warming with phosphorus oxychloride in carbon tetrachloride solution furnished rutaecarpine. This synthesis was completed in 1928 by the same authors by the preparation of 3-)S-amino-ethylindole-2-carboxylic acid by the action of alcoholic potassium hydroxide on 2-keto-2 3 4 5-tetrahydro-3-carboline. An equally simple synthesis was effected almost simultaneously by Asahina, Manske and Robinson, who condensed methyl anthranilate with 2-keto-2 3 4 5-tetrahydro-3-carboline (for notation, see p. 492) by the use of phosphorus trichloride (see partial formulae II). Ohta has also synthesised rutaecarpine by heating a mixture of 2-keto-2 3 4 5-tetrahydrocarboline with isatoic anhydride at 195° for 20 minutes. 

Heliotrine, CigH2,05N, m.p. 125-6°, [ajn — 75° (CHCI3), yields a methiodide, m.p. 108-111°, and contains one methoxyl group, two hydroxyl groups and a tertiary nitrogen atom. On alkaline hydrolysis it forms heliotridine (p. 607) and heliotric acid (p. 613). In presence of platinic oxide it absorbs two molecules of hydrogen and affords, as scission products, heliotric acid and hydroxyheliotridane (p. 607). 

When monocrotaline is hydrogenolysed the acid scission product is monocrotalic acid, CgHigOj, m.p. 181-2°, [a]p ° — 5-33° (HgO), which provides a methyl ester, m.p. 79-80°, [ ]d°° — 16-2° (EtOH), containing one active H atom and a p-bromophenacyl ester, m.p. 162-3°. It is a lactonic acid, which on boiling with sodium hydroxide solution loses carbon dioxide and produces a/3-dimethyllaevulic acid (monocrotic acid, II). 

Attempts to form a cycloadduct of cyclopent[6]azepine (10) with diethyl diazenedicarboxylate furnished the two isomeric hydrazines 14 and 15, which appear to be the products of direct electrophilic substitution of the cyclopentazepine rather than scission products of the expected [4 + 2] cycloadduct.2... 

Ring contraction to 3 6 fused, e.g. 17, rather than 4 5 fused ring systems, accompanied by phenylation, occurs on treating l//-azepine-l-carboxylates, e.g. 16. with pailadium(II) acetate in benzene solution.242 In solvents other than benzene, ring-scission products result (see Section... 

The presence of the pyranose ring in the two D-glucose units of melezitose was inferred by Zempl6n and Braun from good evidence, and made certain by Miss Leitch29 through the crystallization of the requisite amount of 2,3,4,6-tetramethyl-D-glucose from the scission products of the fully methylated trisaccharide. The revised interpretation of Miss Leitch s experimental data concerns only the structure of the... 

The scission product from the diamagnetic [Ga(BPG)(DTBC)] complex is considerably less (4%) than that from the corresponding Fe complex (97%) (29). Gallium(III) is a diamagnetic d10 ion with an ionic radius very similar to that of iron(III) and expected to possess similar Lewis properties to that of Fe(III). Thus, the results clearly demonstrate that the ability of the metal center to transfer paramagnetic spin density to... 

PBS (Figure 30) is an alternating copolymer of sulfur dioxide and 1-butene. It undergoes efficient main chain scission upon exposure to electron beam radiation to produce, as major scission products, sulfur dioxide and the olefin monomer. Exposure results first in scission of the main chain carbon-sulfur bond, followed by depolymerization of the radical (and cationic) fragments to an extent that is temperature dependent and results in evolution of the volatile monomers species. The mechanism of the radiochemical degradation of polyolefin sulfones has been the subject of detailed studies by O Donnell et. al. (.41). 

The calibration standards included sodium form polystyrene sulfonates obtained from Pressure Chemical Co., Pittsburgh, Pa., and sodium toluene sulfonate. Measurements were taken at 0.5 to I.Oml/mln flow rates. The logarithm of the molecular weight of the standards was linear it suggests a framework for approaching an interpretion of the structure of the scission products. This application of size exclusion chromatography measurements must be viewed as a first approximation because of the unmeasured differences between the chromatographic behavior of the linear standards and the expected branched structure of the scission products. 

The mixture of the reaction products can be shifted from oxidation to reduction products depending on the method chosen to work up the reaction mixture, and can include chain scission products such as alcohols, aldehydes, ketones, carboxylic acids, and diacids. 

The resulting polyol resembles the product that is hypothesized for the oligomerization of triglycerides via air oxidation, with the exception that there is a large increase in the hydroxyl content of the polyol product, and there is very little, if any, of the starting epoxide left unreacted. In addition, the epoxidation process does not produce low molecular weight chain scission products, which are a by-product of the blown oil process. The hydroxylation of epoxidized triglycerides is illustrated in Fig. 17. 

A chemical fingerprint is generated consisting of scission products, in the MS/MS instrument, characteristic of the compound of interest. The parent molecule has a MW of 403. In each case the same major fragments are observed masses 361,301,... 

It would be interesting to measure the yields of -scission products from each n-alkane to determine whether they complement the yields of O-heterocycles. 

Preceding work on MEK oxidation has identified a number of possible reaction networks whereby formation of DA and the numerous observed by-products could be rationalised. Yamazoe et al. (ref. 2) and Ai (ref. 5) have proposed the formation of peroxy intermediates formed by reaction with 02"(a(jS) to explain the formation of DA and C2 scission products. 

Acid-catalyzed cracking and platinum-catalyzed hydrogenolysis proceed simultaneously over dual-function catalysts. The distribution of the scission products is determined by the relative strengths of the acidic and metal-type catalytic components. 

The distillation method (see Alternate Protocol 1) involves recovering malonaldehyde from an acidified food product. It is similar to that of the direct heating approach (see below), except that TBA is reacted only with an aliquot of the distillate. Consequently, physical and chemical interference by extraneous food constituents in the reaction with TBA is minimized because the food is never directly in contact with TBA. Unfortunately, direct heating of a food under acidic conditions enhances the degradation of existing lipid hydroperoxides as malonaldehyde precursors, and generates additional reactive radicals and scission products other than malonaldehyde that can react with TBA (Raharjo and Sofos, 1993). More malonaldehyde or reactive substances will be gener-... 

Reactions of the 3-butenyltetrazene led primarily to /8-scission products rather than products of 4-exo or 5-endo cyclizations thus, the imine and cross-combination products of the allyl radical were obtained [Eq. (1)]. 

Aldehyde Formation. Several investigators observed a marked dominance of hexanal in the volatile products of low-temperature oxidation. At the higher temperatures, however, 2,4-decadienal was the major aldehyde formed (19,20,21). Both aldehydes are typical scission products of linoleate hydroperoxides. Swoboda and Lea (20) explained this difference on the basis of a selective further oxidation of the dienal at the higher temperature, while Kimoto and Gaddis (19) speculated that the carbon-carbon bond between the carbonyl group and the double bond (Type B) is the most vulnerable to cleavage under moderate conditions of autoxidation, while scission at the carbon-carbon bond away from the olefinic linkage (Type A) is favored under stress such as heat or alkali. 

Sequence-selective RNA scission was accomplished by the attachment of oligo-amines to synthetic DNA oligomers [18]. The cleaving agent 16, composed of di-ethylenetriamine (DETA) linked to 19-mer DNA, hydrolyzed linear 30-mer RNA strand 17 in a sequence-selective manner (Scheme 13.4). Hence, treatment of the linear RNA in the presence of DNA-DETA complex 16 and EDTA at pH 8 for 4 h at 50 °C, furnished, with good selectivity, the scission products 18 and 19, albeit with a low conversion (10%) of the starting material. 

Geissoschizine, a scission product of geissospermine, belongs to this group of bases (see Chapterl9). 

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