Acids apocarotenic acid

Saffron, an extract of flowers of Crocus sativus, contains the water-soluble pigment crocin the digentiobioside of apocarotenic acid, crocetin zeaxanthin, a P-carotene and characteristic flavoring compounds. The yellow color of this pigment is attractive in beverages, cakes, and other bakery products. However, use of this colorant is restricted by its high price. 

The literature contains other examples of the chemical oxidation of carotenoids that aim to mimic oxidation processes that potentially occur in vivo. For example, hypochlorous acid, an oxidant produced by polymorphonuclear leukocytes during inflammatory processes, was shown to oxidatively cleave [3-carotene into apocarotenals and shorter chain compounds (Sommerburg et al. 2003). 

The central cleavage of P-carotene 1 is most likely the major pathway by which mammals produce the required retinoids il), in particular, retinal 2, which is essential for vision and is subsequently oxidized to retinoic acid 3 and reduced to retinol 4. An alternative excentric cleavage of 1 has been reported involving scission of the double bond at C7-C8 producing P-8 -apocarotenal 5 (2a,2b) which is subsequently oxidized to 2 (Fig. 1) (2c). The significance of carotene metabolites such as 2, 3 and 4 to embryonic development and other vital processes such as skin and membrane protection is a major concern of medicinal chemistry. 

A C5 synthetic unit which has ylide functionality and which is likewise accessible from 2-hydroxy-2-methyl-but-3-enal-dimethylacetal (27) has proved suitable particularly for the synthesis of apocarotenals. The copper-catalyzed reaction of (27) with triphenylphosphine (15) in the presence of aqueous acid leads to 4-triphenyl-phosphonium-2-methyl-buten-2-al (33). The bifunctional C5 ylenal (34), which is important for carotenoid syntheses, is formed therefrom with proton acceptors. 

Anisic Alcohol, 456 Anisic Aldehyde, 524 Anisole, 456, 606 Anisyl Acetate, 456, 568, 606 Anisyl Acetone, 524 Anisyl Alcohol, 456, 606 Anisyl Formate, 456, 607 Annatto Extracts, 31 Anthrone TS, (Sl)114 Antimony Trichloride TS, 850, 851 APDC Extraction Method, 766 APM, 35, (S 1)4 APM-Ace, (S3)5 APO, 32 Apocarotenal, 32 p-Apo-8 -Carotenal, 32 Apparatus for Tests and Assays, 4, 727 D-Araboascorbic Acid, 134 L-Arginine, 32, (S3)5 l-Arginine Monohydrochloride, 33 Arsenic Specification, Requirements for Keeping, xv... 

Figure 9-2 Structural Formulas of Some Provitamins A. (A) P-carotene, and (B) apocarotenal (R = CHO) and apocarotenoic acid ester (R = COOC2H5).

Figure 2.4. Potential products arising from enzymic or nonenzymic symmetrical (a) or asymmetric (b to d) oxidative cleavage of, 6-carotene. Apocarotenals can undergo side chain oxidation to yield retinoic acid, but cannot form retinaldehyde or retinol.

Carotenoids such as )S-apo-8 -carotenal with its nine conjugated double bonds also form epoxides and lose all their color on oxidation. Thus, experiments using color loss at 460 nm were performed to study antioxidant activity. Table XII shows that y-tocopherol followed by BHA and a-tocopherol are the best antioxidants for apocarotenal, and if AP is added, both tocopherols are the very best. Ascorbic acid and AP both have some antioxidant activity for apocarotenal without tocopherol. 

Experimental optical spectra in the NMR region are reported for protonated adducts of (3-carotene (1), canthaxanthin (16) and an apocarotenal measured in benzene, CH2CI2 and acetonitrile solutions at room temperature [116]. Extinction coefficients were estimated. For 13-carotene (1) in the presence of 0.29 vol% trifluoroacetic acid at A,max 1022 nm in CH2CI2, s = 1.86 105 was determined. The position of A ax for protonated 1 was in the same region as that of radical cations and was only slightly dependent on the solvent. 

The Ci9 conjugated aldehyde component was reacted with the lithium derivative of this Cg acetal in ammonia to afford an hydroxy compound which was dehydrated under mild acidic conditions to the fully conjugated C25 substance. Chain extension with ethyl vinyl ether in the presence of boron trifluoride-zinc chloride and mild acidic deethanolation gave the Cjt acetal which was then converted with prop-1-enyl ethyl ether under the same conditions to the required C30 structure of dehydro-p-apocarotenal. Lindlar partial reduction followed by isomerisation afforded the final product. The route is shown in Scheme 14b Scheme 14b... 

As has been shown in previous Chapters the Wittig and the Horner-Emmons reactions are of utmost importance for the coupling of carotenoid end groups with the polyene chain. In the following example, the synthesis of the naturally occurring C25-apocarotenal 507 (12 -apo-P-caroten-12 -al, (3-apo-12 -carotenal) and also ethyl 8 -apo-P-caroten-8 -oate (1) (P-apo-8-carotenoic acid ethyl ester), which is produced industrially by means of these reactions, is described. 

Saponification is the technique most used for the removal of fatty matter and other components such as chlorophylls (when their analysis is not required). In addition, saponification hydrolyzes the fatty acid esters of xanthophylls present in many ripe fruits, facilitating subsequent stages of analysis (such as isolation, identification, and quantification). The general procedure of pigment extract saponification is usually preceded by a step of transfer to diethyl ether, which is immiscible with water and has a low boiling point (below 35°C), simplifying water removal and its own removal by evaporation. This transfer not only helps saponification, but also prevents the formation of saponification artifacts, above all by reaction between ketones (usually because of the presence of acetone in the extract) and apocarotenal aldehyde groups. 

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