A simple and efficient synthesis of norbixin and crocetin diesters is described following the schemes C2 + C2o + C2,=C24 and C3 + C14 + C3 = C20 respectively. By means of the Wittig reaction crocetin di‐aldehyde is condensed with a bromoacetic acid ester and a C14‐dialdehyde with an α‐bromopropionic acid ester. The intermediate tri‐ phenylphosphorane compounds are crystalline and easily isolated in a pure state.
To study the oxidative degradation of p‐carotene to vitamin A in the animal body, a number of possible intermediates have been prepared. Starting with 15,15′‐dehydro‐β‐apo‐12′‐carotenal(C25) vinylogous series of polyene aldehydes and acetates with 25 to 40 carbon atoms have been synthesized by successive enol ether condensations. The synthetic β‐apo‐8′‐carotenal(C30) and β‐apo‐8′‐carotenal(C30) were identical with the permanganate oxidation product of β‐carotene and its corresponding alcohol isolated by KARRER.
The industrial β‐carotene manufacturing procedure based on Inhoffen's synthesis C19 + C2 + C19 = C40 is described. β‐Ionone is first lengthened to β‐C14‐aldehyde as in our vitamin A‐synthesis. By acetalisation, condensation with vinyl ether and treatment with acid the new β‐C16‐aldehyde is obtained. Repetition of the same reactions with propenyl ether leads to the β‐C19‐aldehyde. For the final steps simple methods were developed giving high yields. All the chemical, physical and biological constants of synthetic β‐carotene are identical with those of the natural compound. Exact data on light absorption are given. Extensive experiments with the synthetic β‐carotene on rats and rabbits show that even very large doses have no toxic effects.
A simple and efficient synthesis of lycopene is described based on stepwise lengthening of a symmetrical C10‐dialdehyde as central component. This C10‐dialdehyde is lengthened at both ends, first with vinyl ether and then with propenyl ether, leading to a C20‐dialdehyde which is transformed into crocetin dialdehyde by partial hydrogenation of the central triple bond. By means of a new reaction devised by Wittig, crocetin dialdehyde is condensed at both ends with geranylidene‐triphenylphosphorane and lycopene is obtained according to the scheme C10 + C20 + C10 = C40. This synthetic pigment is identical with pure natural lycopene isolated from tomato juice. The Wittig reaction also allows a new β‐carotene synthesis using the components cyclogeranylidene‐triphenylphosphorane and 8,8′‐dehydro‐crocetin dialdehyde.
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