Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2001-09-13
2002-04-16
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S348000, C568S362000, C568S374000
Reexamination Certificate
active
06372946
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of direct oxidative conversion of &bgr;-carotene and &bgr;-carotene derivatives such as 3,3′-dihydroxy-&bgr;-carotene (zeaxanthin) to 4,4′diketo-&bgr;-carotene and 3,3′-dihydroxy-4,4′-diketo-&bgr;-carotene (astaxanthin), respectively. In this manner, canthaxanthin, which is a commercial poultry food additive, and astaxanthin, which is a commercial fish food additive, can be prepared from inexpensive naturally derived starting materials.
2. Description of the Related Art
Commercially, astaxanthin is an economically important natural carotenoid which is extensively used in aquaculture to impart natural color in certain species of fish, specifically salmon and trout, as these fish do not have access to these natural pigmentation sources. Likewise, canthaxanthin is a reddish natural pigment which is used in the poultry industry to impart color to the egg yolk and skin. Both compounds are prepared synthetically.
Astaxanthin can be prepared by total synthesis or by algae culture and bacterial fermentation (See, for example, U.S. Pat. Nos. 6,022,701, 6,015,684, 5,972,642 and 5,935,808). The manufacture by total synthesis is costly, requiring expensive raw materials and reagents and is very laborious. The synthesis produces a complete mixture of isomers that are normally not found in nature. The culturing of algae and the fermentation of bacteria produce only low yields of product and mixtures including other carotenoids which make them not suitable for food additives. Likewise, these methods are very costly.
We (patent application No. 09/813,685) have previously described the conversion of zeaxanthin to astaxanthin but the present method provides a cleaner reaction and higher yields. The synthetic conversion of &bgr;-carotene to canthaxanthin has been previously described (U.S. Pat. No. 4,212,827). However, this procedure employs expensive iodide reagents or molecular bromine in order to carry out the oxidation. The present procedure employs hypobromide instead of molecular bromine and does not need the 5 day reaction indicated in the above-cited patent. Masuda et al. (Masuda et al. J. (1994) Org. Chem. 59: 5550-5555) reported that hypobromous acid (BrOH) can be generated from NaBrO
3
and NaHSO
3
. Sakaguchi et al. (Sakaguchi et al. (1997) Bull. Chem. Soc. Jpn. 70: 2561-2566) reported that the above reagent can be used in oxidation of various diols to form ketones. However, the use of hypobromide in the oxidation of complex biomolecules such as &bgr;-carotene and zeaxanthin to form commercially important pigments has not been reported. The presently disclosed method provides a distinct advantage over previously described methods in that the reaction time is significantly reduced.
SUMMARY OF THE INVENTION
In one embodiment of the invention a method of preparing 4,4′-diketo derivatives from &bgr;-carotene or &bgr;-carotene derivatives is described which includes contacting the &bgr;-carotene or &bgr;-carotene derivatives in an organic solvent with a solution of an oxidizing agent, wherein the oxidizing agent is formed by mixing acidified aqueous solutions of the sodium or potassium salts of sulfite, hydrogen sulfite, or bisulfite solutions and sodium or potassium bromate solutions in water to produce 4,4′-diketo derivative products. In one embodiment, the &bgr;-carotene derivative is zeaxanthin and the product is astaxanthin. In an alternate embodiment, &bgr;-carotene is employed and the product is canthaxanthin.
In one embodiment of the described method, the oxidizing agent is formed by addition of an acidified solution selected from the group including sodium or potassium sulfite, sodium or potassium hydrogen sulfite, and sodium or potassium bisulfite to a biphasic media consisting of &bgr;-carotene or &bgr;-carotene derivatives in an organic solvent and either sodium bromate or potassium bromate in an aqueous solvent. In a preferred embodiment, the oxidizing agent is formed by mixing aqueous solutions selected from the group including acidified sodium or potassium sulfite, acidified sodium or potassium hydrogen sulfite, and acidified sodium or potassium bisulfite with aqueous solutions of either sodium bromate or potassium bromate and adding the resulting solution to an organic solvent solution of &bgr;-carotene or &bgr;-carotene derivatives. In a most preferred embodiment, the aqueous solution is acidic. In a preferred embodiment, the &bgr;-carotene derivative is zeaxanthin and the product is astaxanthin. In an alternate preferred embodiment, &bgr;-carotene is employed and the product is canthaxanthin.
In a preferred embodiment of the described method, the organic solvent is chloroform or methylene chloride.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
While the described embodiment represents the preferred embodiment of the present invention, it is to be understood that modifications will occur to those skilled in the art without departing from the spirit of the invention. The scope of the invention is therefore to be determined solely by the appended claims.
The present invention relates to a method for the oxidative conversion of &bgr;-carotene and &bgr;-carotene derivatives to the corresponding 4,4′-diketo-&bgr;-carotene derivatives. Compounds of economic importance such as canthaxanthin and astaxanthin can be formed readily from &bgr;-carotene and zeaxanthin by the disclosed method. The method includes contacting zeaxanthin or &bgr;-carotene in an organic solvent with an oxidizing agent formed by the addition of salts of sulfite, hydrogen sulfite or bisulfite to an aqueous solution of a bromate salt. In a preferred embodiment, the salt is a sodium or potassium salt.
In one embodiment, the reaction solvent is a halogen containing solvent and the pH of the solution is acidic. The bromate and sulfite can be mixed either prior to the reaction or added later during the reaction itself. In a preferred embodiment, zeaxanthin or &bgr;-carotene is slurried or dissolved in chloroform and an aqueous solution containing sodium or potassium bromate. An aqueous solution of sodium hydrogen sulfite is added slowly to effect the reaction. In another preferred embodiment, an aqueous solution of the oxidant is prepared by mixing sodium bromate and sodium hydrogen sulfite and this solution is added to the chloroform solution or slurry of zeaxanthin or &bgr;-carotene to effect reaction.
The present invention also may have some utility in the formation of 4,4′-keto groups of other carotenoid compounds. Such compounds include but are not limited to echinenone, astacene, phoenicopterone, 3-hydroxycanthaxanthin, and 3,3′-dihydroxyechinenone.
The present invention is directed toward a method of treating &bgr;-carotene and &bgr;-carotene derivatives with an oxidizing agent. Non-limiting examples of performing allylic oxidations or agents that may be employed in oxidation reactions have been reviewed in Barry Trost and Ian Fleming, eds. “Comprehensive Organic Synthesis”, Volume 7, Pergamon Press, New York, 1991, Pages 83-117, and Richard C. Larock “Comprehensive Organic Transformations”, Wiley-VCH, New York, 1999, pages 1207-1209, which are incorporated herein in their entirety by refe
Davis Jeffery L.
Schloemer Danuta A.
Schloemer George C.
Prodemex, S.A. DE C.V.
Richter Johann
Witherspoon Sikarl A.
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