Natural racemate

Fig. 12 Force/area curves of stearamide films on 6n H2S04 at 25°C 1, natural racemate II, enantiomeric stearamide III, mixture of solutions of enantiomers on the surface in 1 1 ratio. Reprinted with permission from Arnett and Thompson, 1981. Copyright 1981 American Chemical Society.

Natural racemic mixtures of a-terpineol were detected in geranium oiis87,l80 Morio Muscat-wine aroma. 66 ... 

In the flavour extract of apricots, racemic dihydroactinidiolide (DHA) was found as the first natural racemate detected by enantio-MDGC analysis [16]. The absolute configurations and the optical activities have been reported to be (R)-(-) and (S)- +) enantiomers, respectively [17, 18]. 

Photocyclisation of 1 -benzylidene-2-formyl-6-methoxy-7-benzyloxy-3,4-di-hydroisoquinoline is the key step in the synthesis of bharatamine, a natural racemic protoberberine alkaloid, and thermolysis of l-biaryl-5-morpholino-v-triazolines (134) gives the amidines (135) which will undergo photocyclisation to the 6-alkylphenanthridines (136) following morpholine elimination. These 6-alkylphenanthridines can also be synthesised, but with lower... 

Lupanine Dodecahydro-7tl4-methano 4Hf6H di-pyrido[It2-a r,2 e][lt5]diQzocin-4 one. Cl5HMNaO mol wt 248,36, C 72.54% H 9.74%, N 11.28%, O 6,44%. Racemic lupanine is found in white lupins, d-tupanine is found in blue lupins /-lupanine has been prepd from the natural racemic fnrm. Structure Davis, Arch. Pharm. 235, 199,... 

The crystallization of racemic molecules is very similar to the crystallization of achiral molecules. However, because of their chirality, racemic molecules can form different types of crystals with different compositions. If the crystal lattice contains equal left and right handed molecules arranged in an ordered manner, the crystal is heterochiral and referred to as a racemic compound. In the case where the crystal lattice is composed of only one enantiomer (left or right), the crystal is homochiral and referred to as a conglomerate. In nature, racemic compounds greatly outnumber conglomerates. 

Galenical preparations such as tinctures, dried extracts, and mixtures of Atropa belladonna, Hyoscyamm niger, and Datura stramonium, still find clinical use, but most physicians prefer the pure alkaloids. Scopolamine (5), which is (-)-hyoscine, is more active than (-l-)-hyoscine, while the anticholinergic affects of atropine are almost entirely due to (—)-hyoscyamine (6) which forms 50 per cent of the natural racemate. 

Batista JM, Lopez SN, da Silva Mota J, Vanzolini KL, Cass QB, Rinaldo D, Vilegas W, da Silva Bolzani V, Kato MJ, Furlan M. Resolution and absolute configuration assignment of a natural racemic chromane from Peperomia ohtusifolia (Piperaceae). Chirality 2009 21(9) 799-801. 

A dicyclic monoterpene, the ( + )-form of which is found in oil of savin and many other essentia oils. The (—)- and racemic forms occur occasionally in nature. 

In this preparation, the ( + ) or dextro-rotatory (natural) camphor or the ( ) or racemic (synthetic) camphor can be used. Perform the oxidation in a fume-cupboard. 

Clearly, there is a need for techniques which provide access to enantiomerically pure compounds. There are a number of methods by which this goal can be achieved . One can start from naturally occurring enantiomerically pure compounds (the chiral pool). Alternatively, racemic mixtures can be separated via kinetic resolutions or via conversion into diastereomers which can be separated by crystallisation. Finally, enantiomerically pure compounds can be obtained through asymmetric synthesis. One possibility is the use of chiral auxiliaries derived from the chiral pool. The most elegant metliod, however, is enantioselective catalysis. In this method only a catalytic quantity of enantiomerically pure material suffices to convert achiral starting materials into, ideally, enantiomerically pure products. This approach has found application in a large number of organic... 

Among chiral dialkylboranes, diisopinocampheylborane (8) is the most important and best-studied asymmetric hydroborating agent. It is obtained in both enantiomeric forms from naturally occurring a-pinene. Several procedures for its synthesis have been developed (151—153). The most convenient one, providing product of essentially 100% ee, involves the hydroboration of a-pinene with borane—dimethyl sulfide in tetrahydrofuran (154). Other chiral dialkylboranes derived from terpenes, eg, 2- and 3-carene (155), limonene (156), and longifolene (157,158), can also be prepared by controlled hydroboration. A more tedious approach to chiral dialkylboranes is based on the resolution of racemates. /n j -2,5-Dimethylborolane, which shows excellent enantioselectivity in the hydroboration of all principal classes of prochiral alkenes except 1,1-disubstituted terminal double bonds, has been... 

Lactic acid is also the simplest hydroxy acid that is optically active. L (+)-Lactic acid [79-33-4] (1) occurs naturally ia blood and ia many fermentation products (7). The chemically produced lactic acid is a racemic mixture and some fermentations also produce the racemic mixture or an enantiomeric excess of D (—)-lactic acid [10326-41-7] (2) (8). 

The optical activity of malic acid changes with dilution (8). The naturally occurring, levorotatory acid shows a most peculiar behavior in this respect a 34% solution at 20°C is optically inactive. Dilution results in increasing levo rotation, whereas more concentrated solutions show dextro rotation. The effects of dilution are explained by the postulation that an additional form, the epoxide (3), occurs in solution and that the direction of rotation of the normal (open-chain) and epoxide forms is reversed (8). Synthetic (racemic) R,.9-ma1ic acid can be resolved into the two enantiomers by crystallisation of its cinchonine salts. 

Tartaric acid [526-83-0] (2,3-dihydroxybutanedioic acid, 2,3-dihydroxysuccinic acid), C H O, is a dihydroxy dicarboxyhc acid with two chiral centers. It exists as the dextro- and levorotatory acid the meso form (which is inactive owing to internal compensation), and the racemic mixture (which is commonly known as racemic acid). The commercial product in the United States is the natural, dextrorotatory form, (R-R, R )-tartaric acid (L(+)-tartaric acid) [87-69-4]. This enantiomer occurs in grapes as its acid potassium salt (cream of tartar). In the fermentation of wine (qv), this salt forms deposits in the vats free crystallized tartaric acid was first obtained from such fermentation residues by Scheele in 1769. 

Physical Properties. When crystaUized from aqueous solutions above 5°C, natural (R-R, R )-tartaric acid is obtained in the anhydrous form. Below 5°C, tartaric acid forms a monohydrate which is unstable at room temperature. The optical rotation of an aqueous solution varies with concentration. It is stable in air and racemizes with great ease on heating. Some of the physical properties of (R-R, R )-tartaric acid are Hsted in Table 7. 

Enzymatic hydrolysis is also used for the preparation of L-amino acids. Racemic D- and L-amino acids and their acyl-derivatives obtained chemically can be resolved enzymatically to yield their natural L-forms. Aminoacylases such as that from Pispergillus OTj e specifically hydrolyze L-enantiomers of acyl-DL-amino acids. The resulting L-amino acid can be separated readily from the unchanged acyl-D form which is racemized and subjected to further hydrolysis. Several L-amino acids, eg, methionine [63-68-3], phenylalanine [63-91-2], tryptophan [73-22-3], and valine [72-18-4] have been manufactured by this process in Japan and production costs have been reduced by 40% through the appHcation of immobilized cell technology (75). Cyclohexane chloride, which is a by-product in nylon manufacture, is chemically converted to DL-amino-S-caprolactam [105-60-2] (23) which is resolved and/or racemized to (24)... 

Camphor Manufacture. Camphor is obtained both naturally and synthetically. Natural camphor is obtained from the wood of the camphor tree, Cinnamormum camphora which grows ia China and Japan. The camphor is isolated by combination of steam distillation, filtration, distillation, and sublimation (169). Natural camphor is the (+)-camphor, whereas synthetic camphor is racemic both products are recognized by the USP. In 1995, the price of synthetic camphor was 7.15/kg (45). In 1992—1993, the total production of synthetic camphor ia India was 3800 t, which is estimated to be about 40% of the world consumption (170). The largest single use (80%) of camphor is for religious purposes ia Asian countries. 

Vitamin K compounds ate yellow solids or viscous liquids. The natural form of vitamin is a single diastereoisomer with 2 (E), 7 (R), ll (R) stereochemistry. The predominant commercial form of vitamin is the racemate and a 2 (E)j (Z) mixture. Table 1 fists some physical and spectral properties of vitamin K. ... 

Although the predominant commercial form of vitamin is the racemate, natural (2 (E), 7 (R), 1 h(R))—vitamin is accessible either from a... 

The racemic form of the unsubstituted nucleus (1, X = CH2) was synthesized by several groups (32—34) prior to the disclosure of the natural material. One reaction path involved an azetidinone (21) where R = CH2OH or CH=CH2 converted to the corresponding phosphorane (22) where R = o-NO.-C,H, when R = CH.OH and R = COCH, when R=CH=CH.. 

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