Catalytic Conversion of a Diene into Deeply Coloured Polyenes

Eisler, B.; Wassermann, A.; Farnsworth, F. D.; Kendrick, David A.; Schnurmann, Robert

doi:10.1038/168459a0

Cited by 8 publications

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“…A given metabolite, however, might well accumulate as a result of inadequate thiamine. which could initiate or terminate a polymerization (18). This is not to suggest that individual syntheses would be expected in each case.…”

Section: Pigmcntmentioning

confidence: 98%

“…To this might well be added the likelihood of the initial attack occurring where double bond character is at its greatest for a given stereoisomeric configuration, The rupture would then obviously be ex pected at a point of greatest instability, Thus, under a given set of condi tions, the organism might produce epoxides, furanoids, or even cleavage products such as crocetin or vitamin A, In the photooxidation of chlorophyll preparations, Lonie & Ritchie (17) obscrvcd an oxygen : carotene mole ratio of unity. They considered their final stable product to be a hydroperoxide, and in manometric studies, they noted a partial reversibility on lowering the oxygen partial pressure, A direct synthesis.-The synthesis of a polyene directly from cyclopenta diene (18) has been studied kinetically, and three elementary steps have been deduced, namely initiation, propagation, and termination. The compound, a polycyclopentadiene, was isolated as the trichloroacetic acid adduct.…”

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Carotenoids

Mackinney¹

1952

Annu. Rev. Biochem.

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A period of descriptive and analytical examination of the carotenoids has now reached a culminating point with the complete synthesis of vitamin A and of representative carotenoid pigments." Thus Endeavour introduces a definitive discussion by Heilbron & Cook (1) on carotenoids and vitamin A. Total synthesis of the common carotenes has been achieved, those of {j-carotene (2) and lycopene (3) being of special interest. The synthesis of an artificial carotenoid free from the limitation of the normal C40 skeleton, yet retaining the cyclohexenyl rings and the isoprenic pattern, a decapreno-,6carotene (Le., with 10 isoprene units), C50H68 (4), gives emphasis to the re mark that a culminating point has been reached, that it is indeed the end of a chapter (1).Two other remarks may be singled out for attention: "that the polyene system as it occurs in the carotenoids remains one of largely unknown po tentialities," and, secondly, that "attention wiII undoubtedly be increasingly directed to the role of these substances in the living cell." It is proposed to elaborate upon these points in this review, with particular emphasis on the biosynthesis of carotenoids.Customary omissions include aspects considered in other chapters, on nu trition, fat-soluble vitamins, and photosynthesis. Carotenoid metabolism in marine invertebrates and the nature of carotenoids found in deep sea muds have already been discussed by Fox (5). Because of a review on the biochem istry of vision next year, the role of carotenoids in the visual purple cycle is also omitted.1 GENERAL Nomenclature.-Carotenoid nomenclature offers difficulties for reasons listed by Zechmeister (6), and sympathy with several of his objections to the report of the Committee on Biochemical N omenc1ature (7) may be expressed. Full discussion of all views is essential, though ultimately compromises or arbitrary decisions are inevitable, and there may indeed be reservations over some of Zechmeister's objections. As he rightly suggests, the pigment C4DH68 should not be termed carotene, but dihydrocarotene. However, we are then confronted with the dilemma of r-carotene, a simple and useful designation for a natural carotenoid hydrocarbon pigment considered by Porter & Lincoln (8) to be an octahydrolycopen�. For simplicity and ease of reference in the immediate future, a useful distinction might be to retain designations such as t-carotene and even If-carotene (9) for naturally oc-I The survey of the literature ' pertaining to this review was completed in De cember. 1951. 473 Annu. Rev. Biochem. 1952.21:473-492. Downloaded from www.annualreviews.org Access provided by University of Washington on 02/05/15. For personal use only. Quick links to online content Further ANNUAL REVIEWS 474 MACKINNEY cUfring hydrocarbons, but not for syntheti� products such as dihydrocaro tene.A second reservation involves unambiguous usage of the prefixes pro and proto-. The Committee may not have followed the most desirable usage with regard to designating precursors, but it can be defended against seri...

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Section: Pigmcntmentioning

confidence: 98%

mentioning

confidence: 99%

Carotenoids

Mackinney¹

1952

Annu. Rev. Biochem.

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“…The behavior corresponds to that observed by Wassermann and his explanation seems to be applicable. Either the dimerization of the cyclopentadiene may be catalyzed by acids or the acids may be involved in a teleomerization, such as has actually been observed (8,9).…”

Section: VIImentioning

confidence: 99%

Methods for Acceleration of a Typical Diels-Alder Reaction

Rodgman¹,

Wright²

1953

J. Org. Chem.

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An addition reaction such as that of Diels and Alder, which occurs with a marked decrease in entropy is obviously favored by low temperature. However in many cases elevated temperatures are required in order to attain equilibrium wit,hin a reasonable time. It is apparent that conditions permitting reaction at moderate temperatures are desirable. In the present report it will be shown that these conditions include choice of reaction medium and inclusion of acidic catalysts. Our observations have partly been anticipated by Wassermann, et al.( l ) , who reported the catalytic effect of acids on the reaction between benzoquinone and cyclopentadiene.The reaction which we have chosen for study is the original one of Diels and Alder (2, 3). We chose the addition of dialkyl azodicarboxylate (I) to cyclopentadiene (11) because the diene and the adduct, 1,2-dicarboalkoxy-3,6-COOR N N COOR /I &?TC 0 0 R (i) I I1 I11endomethylene-1 ,2,3,6-tetrahydropyridazine (111) are colorless in the spectral range over which I is highly absorptive of light. Furthermore solutions of the colored ester follow Beer's Lam closely. We were thus able to examine the kinetics of the reaction. When benzene, dioxane, or petroleum ether (b.p. 60-70') is used as the medium the reaction between ester (I) and diene (11) can be described fully by equation (i). The over-all reaction appears to be second-order, first order in respect of either ester or diene. This is in agreement with the kinetic results obtained by other authors for the Diels-Alder reaction both in the gas phase and in solution (4). An example of extensive investigations using the dimethyl and the diethyl ester and cyclopentadiene in benzene is shown in Table I. The calculation of the specific rate constants in Table I adapted the usual second order rate expression : k = ! [ w h e n a = h t a -x aJ (ii) or 2.303 b(ax) (ab)t log a(bx) k = when a # b (iii) 465

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The significance of some parameters in formulas of polymerization kinetics

Murphy

Wassermann

1954

J. Polym. Sci.

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A treatment of polymerization reactions is described that involves the assumptions that: (a) intermediates of short lifetime play a role and (b) the velocity coefficients of propagation, (kp)r, and of termination, (kt)r, vary with the chain length, r, of the growing polymers. General formulas are derived and it is shown that they reduce to the previously deduced formulas if the ratio kt/kp is independent of r. Identical formulas can also be deduced, however, if the ratio (kt)r/(kp)r depends on r in a specified manner. Agreement between the previously deduced formulas and the results of experiments does not prove, therefore, that the ratio (kt)r/(kp)r is actually independent of the chain length.

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Catalytic Conversion of a Diene into Deeply Coloured Polyenes

Cited by 8 publications

References 3 publications

Carotenoids

Carotenoids

Methods for Acceleration of a Typical Diels-Alder Reaction

The significance of some parameters in formulas of polymerization kinetics

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