Resolution carboxylic acids

Di- and tri-carboxylic acids. Resolution by anion-exchange chromatography. [Bengtsson and Samuelson Anal Chim Acta 44 217b 1969.]... 

Hydrolysis Esters Alcohols and carboxylic acids Synthesis of alcohols and carboxylic acids resolution of esters, alcohols, acids Lipase, esterase, protease... 

Nitriles Carboxylic acids Synthesis of carboxylic acids resolutions of acids Nitrilase... 

It is also possible to measure microwave spectra of some more strongly bound Van der Waals complexes in a gas cell ratlier tlian a molecular beam. Indeed, tire first microwave studies on molecular clusters were of this type, on carboxylic acid dimers [jd]. The resolution tliat can be achieved is not as high as in a molecular beam, but bulk gas studies have tire advantage tliat vibrational satellites, due to pure rotational transitions in complexes witli intennolecular bending and stretching modes excited, can often be identified. The frequencies of tire vibrational satellites contain infonnation on how the vibrationally averaged stmcture changes in tire excited states, while their intensities allow tire vibrational frequencies to be estimated. 

This method is widely used for the resolution of chiral amines and carboxylic acids Analogous methods based on the formation and separation of diastereomers have been developed for other functional groups the precise approach depends on the kind of chem ical reactivity associated with the functional groups present m the molecule... 

The latter approach is used in the enantioselective determination of a Phase I metabolite of the antihistaminic drug, terfenadine. Terfenadine is metabolized to several Phase I compounds (Fig. 7-13), among which the carboxylic acid MDL 16.455 is an active metabolite for which plasma concentrations must often be determined. Although terfenadine can be separated directly on Chiralpak AD - an amy-lose-based CSP - the adsorption of the metabolite MDL 16.455 is too high to permit adequate resolution. By derivatizing the plasma sample with diazomethane, the carboxylic acid is converted selectively to the methyl ester, which can be separated in the presence of all other plasma compounds on the above-mentioned CSP Chiralpak AD [24] (Fig. 7-14). Recently, MDL 16.455 has been introduced as a new antihistaminic drug, fexofenadine. 

The most common method of resolution uses an acid-base reaction between a racemic mixture of chiral carboxylic acids (RC02H) and an amine base (RNH2) to yield an ammonium salt. 

The synthesis of key intermediate 12, in optically active form, commences with the resolution of racemic trans-2,3-epoxybutyric acid (27), a substance readily obtained by epoxidation of crotonic acid (26) (see Scheme 5). Treatment of racemic 27 with enantio-merically pure (S)-(-)-1 -a-napthylethylamine affords a 1 1 mixture of diastereomeric ammonium salts which can be resolved by recrystallization from absolute ethanol. Acidification of the resolved diastereomeric ammonium salts with methanesulfonic acid and extraction furnishes both epoxy acid enantiomers in eantiomerically pure form. Because the optical rotation and absolute configuration of one of the antipodes was known, the identity of enantiomerically pure epoxy acid, (+)-27, with the absolute configuration required for a synthesis of erythronolide B, could be confirmed. Sequential treatment of (+)-27 with ethyl chloroformate, excess sodium boro-hydride, and 2-methoxypropene with a trace of phosphorous oxychloride affords protected intermediate 28 in an overall yield of 76%. The action of ethyl chloroformate on carboxylic acid (+)-27 affords a mixed carbonic anhydride which is subsequently reduced by sodium borohydride to a primary alcohol. Protection of the primary hydroxyl group in the form of a mixed ketal is achieved easily with 2-methoxypropene and a catalytic amount of phosphorous oxychloride. 

Several early reports dealt with the resolution of racemic aziridine-2-carboxylic acids [72, 73], Treatment of ( )-78 (Scheme 3.25) with (-)-trans-2,3-bis(hydroxydi-phenylmethyl)-l,4-dioxaspiro[5.4]decane (79), for example, afforded the 1 1 ratio inclusion compound 80. Upon distillation, the inclusion compound 80 gave en-antiomerically pure (-)-78 in 33% yield. 

Most resolution is done on carboxylic acids and often, when a molecule does not contain a carboxyl group, it is converted to a carboxylic acid before resolution is attempted. However, the principle of conversion to diastereomers is not confined to carboxylic acids, and other groupsmay serve as handles to be coupled to an optically active reagent. Racemic bases can be converted to diastereomeric salts with active acids. Alcohols can be converted to diastereomeric esters, aldehydes to diastereomeric hydrazones, and so on. Even hydrocarbons can be converted to diastereomeric inclusion... 

Enantiopure (R)- and (S)-nipecotic acid (Nip) derivatives 64 were obtained following classical resolution of ethyl nipecotate with either enantiomer of tartaric acid and successive recrystallization of the corresponding salts [153, 154, 156] or by resolution of racemic nipecotic acid with enantiomerically pure camphorsul-fonic acid [154]. N-Boc protected pyrrolidine-3-carboxylic acid (PCA) 65 for the synthesis of homo-ohgomers [155] was prepared by GeUman from trans-4-hydroxy-L-prohne according to a known procedure [157]. 

One of the most important characteristics of IL is its wide temperature range for the liquid phase with no vapor pressure, so next we tested the lipase-catalyzed reaction under reduced pressure. It is known that usual methyl esters are not suitable for lipase-catalyzed transesterification as acyl donors because reverse reaction with produced methanol takes place. However, we can avoid such difficulty when the reaction is carried out under reduced pressure even if methyl esters are used as the acyl donor, because the produced methanol is removed immediately from the reaction mixture and thus the reaction equilibrium goes through to produce the desired product. To realize this idea, proper choice of the acyl donor ester was very important. The desired reaction was accomplished using methyl phenylth-ioacetate as acyl donor. Various methyl esters can also be used as acyl donor for these reactions methyl nonanoate was also recommended and efficient optical resolution was accomplished. Using our system, we demonstrated the completely recyclable use of lipase. The transesterification took place smoothly under reduced pressure at 10 Torr at 40°C when 0.5 equivalent of methyl phenylthioacetate was used as acyl donor, and we were able to obtain this compound in optically pure form. Five repetitions of this process showed no drop in the reaction rate (Fig. 4). Recently Kato reported nice additional examples of lipase-catalyzed reaction based on the same idea that CAL-B-catalyzed esterification or amidation of carboxylic acid was accomplished under reduced pressure conditions. ... 

If, according to a modified Horeau method (partial kinetic resolution of a racemate), an optically active carboxylic acid is treated with an excess of racemic amine or alcohol, the configuration of the carboxylic acid can be inferred from the optical rotation of the residual amine or alcohol [48]... 

Use of the relatively small cyclopropane ring drastically reduces the potential for deleterious steric bulk effects and adds only a relatively small lipophilic increment to the partition coefficient of the drug. One of the clever elements of the rolicyprine synthesis itself is the reaction of d,l tranylcypromine (67) with L-5-pyrrolidone-2-carboxylic acid (derived from glutamic acid) to form a highly crystalline diastereomeric salt, thereby effecting resolution. Addition of dicyclohexylcarbodiimide activates the carboxyl group to nucleophilic attack by the primary amine thus forming the amide rolicyprine (68). 

Seifert, W.K. Teeter, R.M. Preparative Thin-layer Chromatography and High Resolution Mass Spectrometry of Crude Oil Carboxylic Acids, Anal. Chem. 1969, 41, 786. 

Adam, W., Lazarus, M., Boss, B. et al. (1997) Enzymic resolution of chiral 2-hydroxy carboxylic acids by enantioselective oxidation with molecular oxygen catalyzed by the glycolate oxidase from spinach (Spinacia oleracea). The Journal of Organic Chemistry, 62 (22), 7841-7843. 

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