Ita-conic acid

Two classes of a-hydroxylated lignans have been enantioselectively prepared a) wikstromol (3) [10, 38] and related natural products [39] and b) gomisin A (1) and congeners [40, 41]. In both cases, chiral, non-racemic ita-conic acid derivatives have been synthesized as key compounds for the preparation of -benzyl-y-butyrolactones (either by resolution (g [32]) or by asymmetric hydrogenation (h [25])). 

Citra-conic. Mesa-conic and Ita-conic Acids... 

Ita-conic Acid.—There is, however, a third acid known of the same composition as the two preceding. It is called ita-conic acid and like the others is obtained from citric acid by distiUation. More than the two isomers just explained are not possible according to geometric isomerism. The isomerism, therefore, of this new acid with the other two must be explained in some other way and has been shown to be structural isomerism due to the different position of the double bond. We have spoken of the fact that both citra-conic and mesa-conic acids, by the addition of hydrogen, are converted into methyl succinic acid. This same result is obtained with ita-conic acid also as may be explained by the following reactions. 

Ita-conic acid, however, yields 2- hrom-methyl) butan-di-oic acid. 

The constitution of ita-conic acid as methylene succinic acid is thus established. Di-basic acids which contain a triple bond and, therefore, related to propin-oic acid are known but will not be considered. 

A few of the more important ones are listed in Tab. 1. Our colleagues at Hoff-mann-LaRoche have added about a dozen more nonaromatic members to this list using DIPAMP. This generality can be extended to a variety of enol esters and ita-conic acid derivatives. Evidently what is required is the ability to chelate with the metal. Thus, the nitrogen atom can be replaced with an oxygen atom or a methylene group (1-3, Fig. 9) [3],... 

Citraconic Acid. 2-Methyi-2-butenedioic acid methylmaleic acid. C H604 mol wt 130.10. C 46.16%, H 4-65%, O 49.19%. Obtained by carefully heating citric acid at about 175. Production o( citraconic anhydride from ita -conic acid Humphrey. U.S. pat. 2.966,498 (i960 to Pfizer). 

Typical examples of this elass of substrates include atropic acid (AA), ita-conic acid (lA) and their methyl esters. With those substrates enantioselec-tivities tend to be somewhat lower eompared to a-dehydroamino acids/ but at present many P-stereogenie ligands have provided excellent results (Table 7.4). 

As noted earher, copolymers currently used in conventional GIs are water-soluble polyelectrolytes having carboxylic acid groups directly or very closely attached to the copolymer backbone. The two primary examples are poly(acrylic acid-co-ita-conic acid) (Fig. 4) or poly(acrylic acid-co-maleic acid) (Fig. 5) both are currently used in commercial formulations. 

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