Dextro form

A chiral molecule is one which exists in two forms, known as enantiomers. Each of the enantiomers is optically active, which means that they can rotate the plane of plane-polarized light. The enantiomer that rotates the plane to the right (clockwise) has been called the d (or dextro) form and the one that rotates it to the left (anticlockwise) the I (or laevo) form. Nowadays, it is more usual to refer to the d and I forms as the ( + ) and (—) forms, respectively. 

Dextro Form. To the filtrate A immediately after the removal of the levo diastereoisomer J is added 2 g. of ammonium bromide. The sides of the flask are scratched with a glass rod and the mixture allowed to crystallize at 20 to 25° for 5 minutes. The impure d-bromide is collected and washed once on the Buchner with 10 ml. of ice water. From the filtrate B dZ-[Co(en)2(N02)2]I can be recovered by the addition of sodium or potassium iodide, 5 g. being a sufficient amount (yield approximately 40%). The impure... 

Right-handed and Left-handed Molecules. Every amino acid except glycine can exist in two isomeric forms. These two forms, called L (levo) and n (dextro) forms, are identical with one another except for the arrangement in space of the four groups attached to the a-carbon atom. The two molecules are mirror images of one another- one can be called the left-handed molecule, and the other the right-handed... 

Isomerism.—Isomerism in the case of the acids is of the same character as that of the alkyl halides and the alcohols if we consider the acids as mono-carboxyl substitution products of the hydrocarbons. In the five carbon acids, the pentanoic or valeric acids, we have one compound which possesses an asymmetric carbon atom. It is the 2-methyl butanoic-i acid. According to the van t Hofif-LeBel theory this compound should exist in three forms, dextro lew and inactive. By oxidation of the fermentation amyl alcohol which is a mixture of 2-methyl butanol-1 and 2-methyl butanol-4 there is obtained a mixture of two of the valeric acids, viz., the 2-methyl butanoic-i acid and the 2-methyl butanoic-4. This same mixture is found naturally in the roots of Valeriana officinalis. By separating out the 2-methyl butanoic-4 acid the 2-methyl butanoic-1 acid is obtained. This acid is inactive, but has nevery with certaintyy been separated into its optical components, though it is claimed that a dextro form has been obtained. 

One of the above formulas may be taken to represent the dextro form and the other the levo. The mixture of the two will produce the inactive acid. Now these three forms of tartaric acid are all known and they bear to each other exactly the same relation as has been explained in connection with lactic acid. The inactive form is able to be split into its two optical components like the inactive lactic acid. These three acids are as follows,... 

It must be emphasized, that the designations d-, dextro and /-levo for the stereo-isomers, refers wholly to their configuration in space and has no reference to the optical activity, so far as the direction of the rotation is concerned, for this may be the same or different. This is illustrated by the fact that d-glucose, which itself is dextro rotatory, by means of its osazone and osone, is converted into the corresponding ketose sugar which, therefore, must be the dextro form of fructose. It is, however, levo in the direction of its optical rotation, i.e., d-/ructose is levo-rotatory. 

Derivatives of Menthene.— The most important alcohols and ketones derived from the menthene unsaturated group of terpenes are terpineol, di-hydro carveol, di-hydro carvone and pulegone. The first one, the alcohol terpineol, occurs in its dextro form in cardamon oil and marjoram oil, in its leoo form in neroU oil and in its inactive form in cajeput oil. The constitution is proven by Perkin s synthesis from As-tetra-hydro para-toluic acid by means of the Grignard reaction. 

Sympathomimetics are also generally optically active drugs, with only one stereoisomer conferring most of the clinical efficacy of the racemate for instance laevo-noradrenaline is at least 50 times as active as the dextro- form. Noradrenaline, adrenaline and phenylephrine are all used clinically as their laevo-isomers. 

Hyoscyamine is Ihe lero form of Ihe racemie mixture known as atropine. The dextro form does not exist naturally but has been synthesized. Cushny compared the activities of (-)-hyoscyamine. (-) )-hyoseyaminc. and Ihe racemate (atropine) in 1904 and found greater peripheral potency for Ihe (-) isomer and twice Ihe potency of the racemate. All later studies have essentially confirmed that the (-)-) isomer is only weakly active and that Ihe (-) i.somer is. in effect. Ihe active portion of alropinc. Inspection of the relative do.ses of alropinc sulfate and hyo.scyamine sulfate illustrates the differences very nicely. The principal criticism offered against the use of hyoscyamine. sulfate cxclu.sively is that it lends to rdccmizc to atropine sulfate rather easily in solution, so that atropine sulfate llicn becomes the more stable of Ihe two. All of the isomers behave very much the. same in Ihe CNS. 

Amphetamine (Benzedrine, Dexedrine) H H H ch3 H Anorectic, narcolepsy, hyperkinesisd marketed as racemic and dextro forms... 

Ctmphene. 2,2-Dimethyl-3-methylenebicyclo-(12. l]beplane 2,2-dimethyl-3-methylenenorbornane 3,3-dimethyl-2-methylenenorcamphane. C,0HU mol wt 136.23. C 8 . 16%, H [1.84%. Occurs in many essential oils, such as tnpeatine (levo and dextro forms), in cypress oil (dextro form), in camphor oil from species of Lauraceae (dextro), in bergamot oil, in oil of citronella, neroli, ginger, valerian. Reviews on isolation, preparation and properties J. L. 

As an example of the co-existence of systematic, semi-systematic and trivial names, we could look at the monoterpenoid ketone, carvone. Carvone occurs in both enantiomeric forms in nature, the laevo-form in spearmint and the dextro-form in caraway. The trivial name carvone is derived from the Latin name for caraway, Carum carvi. The basic carbon skeleton is that of l-isopropyl-4-methylcyclohexane. This skeleton is very common in nature and is particularly important in the genus Mentha, which includes various types of mint, since it forms the backbone of most of the important components of mint oils. The skeleton has therefore been given the name p-menthane and the numbering system used for it is shown in Figure 1.3. Therefore, any of the following names may be used to describe the same molecule carvone, p-mentha-1,8-dien-6-one and 1 -methyl-4-(l-methylethenyl)cyclohex-l-ene-6-one. To classify it, we could say it was an unsaturated ketone of the /7-menthane family of monoterpenoids. 

An active form of an acid may be obtained from the inactive variety by subjecting it to the action of certain bacteria, which destroy one form of the acid more rapidly than the other. In the case of lactic acid the dextro form may be obtained by the action of the mould called penicillium glaucum on inactive ammonium lactate. When lactic acid is made by the fermenta-... 

Scholtz first isolated bebeerine from the commercial powder in levorotatory form (56), but later he was able to isolate also the dextro form (60, 62) as well as a fraction claimed to be the racemic form on the basis that he could also obtain it by mixing chloroform solutions of the dextro- and... 

The physiological action of dextro, levo, and racemic forms of bebeerine has been studied (61, 62). Injections of solutions of their salts into animals brought results dependent upon the animal and upon the rotation of the alkaloid. The dextro form was found to be much more toxic to rabbits, cats, and white mice than the other forms, while in dogs it had little effect. 

The active dextro form, containing the two dextro rotating molecules. 

The importance of this reaction relies on the fact that the Betti bases can function as both excellent ligands and auxiliaries in asymmetric synthesis. The racemic Betti amines can be separated into their optical antipodes. In this respect, among the Betti bases from monochlorobenzaldehydes, only the dextro form of the ortho and meta chloro compounds could be resolved with satisfaction, while the levo antipodes are extremely difficult to obtain due to their higher solubilities. ... 

A racemate may also be resolved by forming a salt or ester with an optically active base (usually an amine) or alcohol. For example, a racemate of an acidic substance A with, say, the dextro form of an optically active base B will give... 

Hgure 1 Structures of stereoisomer of amphetamine and methamphetamine. Note The references to the stereoisomer of amphetamine and methamphetamine are often designated using various different indications of the orientation. Common designations for the dextro form of the drugs include d, d, d, S, and (+) and similarty for the levo form the designations I, I, l, R, and (-) are used. 

Amebiasis - Studies on the synthesis of emetine and its relatives continue and evidence is presented suggesting that the activity and toxicity of racemic 2-dehydroemetine are attributable principally to the levo enantiomer, while the dextro form is relatively inactive. vitro and in amebic liver abscess of the hamster no difference in activity could be detected between natural levo emetine, racemic 2-dehydroemetine and levo-2-de-hydroemetine49. Against rat caecad infections natural levo emetine and levo 2-dehydroemetine had similar activities, about twice that of racemic 2-dehydroemetine. The more active compounds were also about twice as toxic. 

The most important chemically established compound is a-lipoic acid, the cyclic disulfide of 6, 8-dithiooctanoic acid. This has been isolated in crystalline form from acid-hydrolyzed liver, and also prepared synthetically. Thioctic acids with the —SH groups in different positions than the 6, 8 carbons have also been prepared. Because of the asymmetry of Ce of the octanoate chain, the compound is optically active the dextro form is believed to be the one biologically active. The synthetic DL-form has only half of the activity of the natural product in certain enzyme reactions. 

Rose oxide is found in a number of essential oils, but particularly those of rose and geranium. It is used to give dry, green, and rosy top-notes to fragrances. Racemates and optically pure (both laevo- and dextro-) forms are commercially available and used in fragrances. The homochiral products, especially the laevorotatory ones, command much higher prices than does the racemate. 

It is important to differentiate the two forms of carnitine, which are L-camitine and D-camitine (Dextro form). L-camitine is the physiologically active form and is endogenously produced within the human, whereas D-camitine is not physiologically active and is a synthetic. Research has shown that subjects given D-camitine saw a depletion of their endogenous stores of L-camitine, 3-which may manifest itself as carnitine deficiency, especially during intense bouts of exercise. Supplementation of D-camitine is therefore not recommended because it may have a deleterious effect on the body as well as performance. 

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