Carotenoids partial synthesis

Liaaen-Jensen S. 1996. Partial synthesis of sulfates. In Britton G, Liaaen-Jensen S,PfanderH, eds. Carotenoids, Vol. 2 Synthesis. Birkhauser, Basel, Switzerland. 

Terpenoids Sesquiterpenoids Diterpenoids Triterpenoids Carotenoids and Polyter-penoids Steroids Physical Methods Steroid Reactions and Partial Synthesis. 

Partial synthesis of carotenoid sulphates is effected from carotenols by reaction with a sulphur trioxide/pyridine complex prepared from chlorosulphinic acid and pyridine, followed by sodium salt formation by... 

O 8.21%. Carotenoid pigment. Often found in plants, but in minute amounts only and never as a principal pigment. Has same structural formula, mp, rotation, and absorption as chrysanthemaxanthin, <7. V., but differs sterical -ly. Isoln from Ranunculus acris L., Ranuncuiaceae Kuhn, Brockmann. Z. Physiol. Chem. 213, 192 (1932). Structure Karrer, Rutschmann, Heiv, Ckim. Acta 25, 1144 (1942). Partial synthesis Karrer, Jucker, ibid. 28, 300 (1945). 

Besides the Cio-dial 45, crocetindialdehyde (27), the central C2o-dialdehyde, is of utmost importance, especially for the synthesis of acyclic carotenoids. Partially protected dials, which are often necessary for the synthesis of unsymmetrical carotenoids, have also been prepared. The C2o-dial 27 is synthesized by the Wittig reaction of the Cio-dial 45 with the Cs-phosphonium salt 52 (Scheme 12). 

In conclusion, it is evident that the Koenigs-Knorr reaction gives low yields for the glucosidation of carotenoids that bear a secondary hydroxy group in a ring system. Further investigations of the partial synthesis of these compounds, by use of new, recently developed approaches, are imperative and will be useful also for structure elucidation. 

All carotenoid sulphates have been prepared by partial synthesis from the corresponding carotenols by reaction with a sulphur trioxide/pyridine complex prepared from chloro-sulphonic acid and pyridine [8-10], followed by sodium salt formation by addition of NaOH or, for alkali-labile carotenoids, NaCl [11], Scheme 1. The presumed mechanism is that S-0... 

The various parts of Chapter 3 describe the preparation of polyene synthons and the synthesis of different groups of carotenoids, the partial synthesis of carotenoid glycosides, glycosyl esters and sulphates. Technical synthesis and the synthesis of isotopically labelled carotenoids are also covered. 

Excepting the carotenoids obtained at industrial scale, and thus commercially available ( -carotene, canthaxanthin, astaxanthin, (3-apo-8 -carotenal, (3-apo-8 -caro-tenoic ethyl ester and, citranaxanthin), carotenoid standards must be obtained either by total or partial synthesis, or from natural sources in which their presence is confirmed using the extraction and separation techniques described above. Table 6.2 (presence and distribution of the most common carotenoids in foods) can be used to choose the natural source from which carotenoid pigment standards can be obtained. 

Some carotenoids are obtained in the laboratory from another related carotenoid, by means of partial synthesis, which include the reactions described in the identification of functional group section. For example, auroxanthin and luteoxanthin are obtained from violaxanthin by acidification. Neochrome and mutatoxanthin are obtained from neoxanthin and antheraxanthin, respectively, using the same procedure. The Z- 3-carotene isomers are prepared by reflux heating at 200°C an acetone solution of aU-E 3-carotene obtained from a pigment extract of carrot. ... 

Shimada, A., Ezaki, Y Inanaga, J., Katsuki, T, and Yamaguchi, M. (1981) Partial synthesis of aromatic carotenoids, tedanin, agelaxanfhin A, tefhyatene, and renieratene. Tetrahedron Lett., 22, 773-774. 

Carotenoid oxidation products were not only formed from the parent molecules in order to elucidate structure, they were also obtained by partial or total synthesis or by direct oxidation of carotenoid precursors. Thus, apo-8 -lycopenal was synthesized in 1966 more recently, the ozonide of canthaxanthin was obtained by chemical oxidation of canthaxanthin. ... 

It should be noted that partial or total organic synthesis was used to produce carotenoid oxygenated cleavage products such as, for example, apo-8 -lycopenal (Surmatis et al. 1966). 

The special potential for constructing double bonds stereoselectively, often necessary in natural material syntheses, makes the Wittig reaction a valuable alternative compared to partial hydrogenation of acetylenes. It is used in the synthesis of carotenoids, fragrance and aroma compounds, terpenes, steroides, hormones, prostaglandins, pheromones, fatty acid derivatives, plant substances, and a variety of other olefinic naturally occurring compounds. Because of the considerable volume of this topic we would like to consider only selected paths of the synthesis of natural compounds in the following sections and to restrict it to reactions of phosphoranes (ylides) only. 

The formation of the normally present cyclic carotenoids is Inhibited. The transformation of the acyclic lycopene to the monocyclic gamma-carotene Is partially inhibited and further cyclizatlon to the bicyclic beta-carotene is totally Inhibited. However, when the treatment of the entire tree which Is sprayed with 2,000 ppm MPTA Is conducted preharvest at the fully mature stage of fruit development [2], the carotenoid composition of the endocarp reflects a net synthesis of the cyclic pigments and differs from the pattern seen in the peel as shown in Table II. 

The commercial apo-p-carotenoids ethyl 8 -apo-p-caroten-8 -oate (286) and 8 -apo-p-caroten-8 -al (287) may be prepared from the Cig-aldehyde 53, used in the synthesis of p,p-carotene (2). By reaction of 53 with the Cg-acetal 288 the C25-aldehyde 15,15 -didehydro-12 -apo-p-caroten-12 -al (289) is obtained [115], This compound can be transformed into the Cso-aldehyde 287 by consecutive enol ether condensations first with vinyl ethyl ether (17), to give the C2/-aldehyde 290, and then with prop-1-enyl ether (18), followed by partial hydrogenation and isomerization [116] Scheme 59... 

Horner-Emmons reaction of 46 with the dianion of the Cio-bis-phosphonate 47 smoothly gave the (all- )-carotenoid 48. In the final steps of the synthesis, 48 was deprotected (H2SO4) followed by peracetylation of the free hydroxy groups, partial hydrogenation of the central triple bond (Lindlar catalyst/quinoline) and isomerization. The isolated tetraacetoxy-pirardixanthin (36) proved identical in every respect (UV/Vis, H-NMR, CD) with the acetate of the natural product isolated from Penaeus vannamei [42,43]. 

Oxidation of 5 with Mn02 in acetone led to the acetylenic Cio-dialdehyde 6. Partial hydrogenation over Lindlar catalyst [3,4] provided (2 ,4Z,6 )-2,7-dimethylocta-2,4,6-triene-1,8-dialdehyde (7), which was isomerized to the (all- )-Cio-dialdehyde 8. This Cio-building block 8 (Cio-dialdehyde) is by far the most important unit in carotenoid synthesis. 

Historically, the first synthesis of (Z)-isomers of carotenoids became possible after the introduction of a special palladium catalyst (Lindlar catalyst) for the partial hydrogenation of carbon-carbon triple bonds [4]. Thus (15Z)-P,P-carotene [(15Z)-3] [5] and (11Z,1 l Z)-p,13-carotene [(11Z,1 rZ)-3] [6-8] were obtained as intermediates in the synthesis of the (all- 3 target carotene. This partial hydrogenation of triple bonds, proceeding stereospecifically as a syn addition, is still a valuable method for the synthesis of disubstituted double bonds in the (Z)-configuration. The various reactions used to form carbon-carbon double bonds in the construction of the carotenoid skeleton generally proceed with variable stereoselectivity and result in ( 7Z)-mixtures (Chapter 2 Parts I, HI and IV). 

The units 49 and 50 used in the synthesis of vitamin A are also used in many ways in carotenoid syntheses and are produced industrially in large scale. p-Ionone (17) can be converted into vinyl-p-ionol (51) by ethynylation to 52 and partial hydrogenation [42]. This conversion is also achieved in one step by 1,2-addition of vinylmagnesium chloride 55[43]. The two routes are, in principle, equivalent, and which one is used in practice is decided by conditions on site. In this example, the main considerations are the availability of acetylene (4) and vinyl chloride, operating experience, and permits for handling these materials. The Ci5-phosphonium salt 49 is formed directly from 51 by the action of triphenylphosphine and acid [44,45]. A step involving labile P-ionylidene-ethyl halide is thus avoided. Crystalline (lE,9E)-49 is obtained in excellent yield by reaction of 51 with triphenylphosphine and sulphuric acid in isopropanol/heptane [46]. 

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