Peripheral isomer

The unsymmetrical nature of / -mercaptoethylamine should lead to geometric isomerism among its metal complexes, cis and trans isomers might be expected with the square planar nickel (II) and palladium (II) derivatives and facial and peripheral isomers with cobalt (III). However, during the course of the preparation of various samples in which the procedure and experimental conditions were varied, no evidence of such isomerism was apparent (6, 15). This is particularly evident in the case of the cobalt (III) complex, CoL3. Samples prepared by the addition of cobalt (II) chloride 6-hydrate to strongly basic aqueous solution of the ligand and by displacement of ammonia and (ethylenedinitrilo)-... 

Isomers are distinguished by lettering the peripheral sides of the parent beginning with a for the side 1,2, and so on, lettering every side around the periphery. If necessary for clarity, the numbers of the attached position (1,2, for example) of the substituent ring are also denoted. The prefixes are cited in alphabetical order. The numbers and letters are enclosed in square brackets and placed immediately after the designation of the attached component. Examples are... 

In the third sequence, the diastereomer with a /i-epoxide at the C2-C3 site was targeted (compound 1, Scheme 6). As we have seen, intermediate 11 is not a viable starting substrate to achieve this objective because it rests comfortably in a conformation that enforces a peripheral attack by an oxidant to give the undesired C2-C3 epoxide (Scheme 4). If, on the other hand, the exocyclic methylene at C-5 was to be introduced before the oxidation reaction, then given the known preference for an s-trans diene conformation, conformer 18a (Scheme 6) would be more populated at equilibrium. The A2 3 olefin diastereoface that is interior and hindered in the context of 18b is exterior and accessible in 18a. Subjection of intermediate 11 to the established three-step olefination sequence gives intermediate 18 in 54% overall yield. On the basis of the rationale put forth above, 18 should exist mainly in conformation 18a. Selective epoxidation of the C2-C3 enone double bond with potassium tm-butylperoxide furnishes a 4 1 mixture of diastereomeric epoxides favoring the desired isomer 19 19 arises from a peripheral attack on the enone double bond by er/-butylper-oxide, and it is easily purified by crystallization. A second peripheral attack on the ketone function of 19 by dimethylsulfonium methylide gives intermediate 20 exclusively, in a yield of 69%. 

The preparations of chlorins described so far by attack of different reagents at a peripheral C — C double bond of the porphyrin macrocycle are all restricted to highly symmetric porphyrins because otherwise complex mixtures of constitutional isomers can be formed. The problem of... 

Relatively selective stimulation of Pi-adrenergic receptors can be achieved with dobutamine. This is a racemic drug of which both isomers activate the Pi-receptor, and in addition the (-) isomer activates ( -receptors whereas the (+) isomer activates p2-receptors the simultaneous activation of ai- and p2-receptors results in no major net effect on peripheral resistance, and thus the overall cardiovascular effects are mediated by Pi-stimulation leading to increases in cardiac contractility and output. Dobutamine is used for the short-term treatment of acute cardiac failure and for diagnostic purposes in stress echocardiography. 

Bioassay of alternate molecular forms supports the view that the ORs are capable of resolving isomeric distinctions in neutral (non-biological) odourants. Stereochemical pairs of odours were tested for differential sensitivities in the blind subterranean mole rat (Spalax ehrenbergi). The subjects responded to one enantiomer, but not to its stereoisomer. Both sexes were attracted to the odour of R-(-)-carvone but unresponsive to S-(+)-carvone in contrast, males and females were repelled by the odour of (+)-citronellol, but not by (-)-citronellol (Heth et al., 1992). The lack of responsiveness by mole rats could be central due to lack of salience, or peripheral due to hyposmia/anosmia for one isomer. Both carvones have distinct odours for the human nose. 

The 31P- and 29Si-NMR specta of 22 confirmed that the exo configuration is preferred at 25°C.14 At higher temperatures (above 38°C), inversion of the configuration of the peripheral phosphorus atom was observed in the 3IP-NMR spectrum that is, 22 rearranges into the endo isomer 22 and vice versa (Scheme 5). 

The second criteria, a different activity spectrum, is met by oxaliplatin (Figure 1.9A), the l isomer of [oxalatol f ra/rv-1,2-diaminocyclohexane)platinum (II)], oxaliplatin, [Pt(II)(oxalato)(DACH)]. This platinum agent is used for secondary treatment of metastatic colorectal cancer.77 Oxaliplatin, like carboplatin, has a kinetically slower leaving group, and is also less nephrotoxic than cisDDP. The limiting toxicity of oxaliplatin is peripheral sensory neuropathy, also seen with cisDDP. The neuropathy affects the extremities and increases in incidence and... 

Ono Y, Takeuchi Y, Hisanaga N. 1981. A comparative study on the toxicity of -hexane and its isomers on the peripheral nerve. Int Arch Occup Environ Health 48 289-294. 

The alkaloids namely atropine, hyoscyamine and scopolamine are obtained from Atropa belladonna. Atropine is dl-hyoscyamine, and, 1-isomer is more potent than d-form both peripherally and centrally. Atropine blocks the muscarinic effects of acetylcholine, the antagonism between acetylcholine and atropine is of competitive... 

Fenoldopam is a peripheral arteriolar dilator used for hypertensive emergencies and postoperative hypertension. It acts primarily as an agonist of dopamine D receptors, resulting in dilation of peripheral arteries and natriuresis. The commercial product is a racemic mixture with the (R)-isomer mediating the pharmacologic activity. 

Resuscitation from bupivacaine cardiovascular toxicity is extremely difficult even for experienced clinicians. Recent studies suggest that propofol can be useful in resuscitating patients acutely exposed to toxic levels of bupivacaine. The (S)-isomer, levobupivacaine, appears to have a lower propensity for cardiovascular toxicity than the racemic mixture or the (7 >isomer and has been approved for clinical use. The clinical effects of ropivacaine are similar to those of bupivacaine, but ropivacaine is allegedly associated with a lower potential for cardiovascular toxicity. Ropivacaine is available only as the ( SJ-stereoisomer, which has inherently less affinity for the cardiac sodium channel. However, both cardiac toxicity and CNS toxicity have been reported when large doses of ropivacaine were used for peripheral nerve blocks. 

Amphetamine, its derivatives and isomers are used mainly for their CNS effects which will be discussed later. They were once the drug of choice for appetite suppression(PNS and CNS effect) and were used for asthma. Effects related to their peripheral activity are anorexia, increased blood pressure, nausea, vomiting, diarrhea, and cardiac arrhythmias. 

In the IUPAC system, the four methine positions are conveniently numbered 5, 10, 15 and 20, and the eight remaining peripheral positions fall at 2, 3, 7, 8, 12, 13, 17 and 18. The nitrogen atoms are numbered 21 through 24. Owing to the continued use of trivial names, both in the IUPAC and classical systems of nomenclature, certain other features of porphyrin notation and isomerism need to be explained. If the eight peripheral substituents are made up of two sets of four (for example, four methyls and four ethyls), and if there is one of each on the individual pyrrole subunits (a situation which usually occurs in biologically derived porphyrins), then there are four possible so-called primary type isomers. These four isomers for the methyl/ethyl series, trivially named etioporphyrins, are shown in Scheme 1 the compounds are named etioporphyrin-I (14), etioporphyrin-II (15), etioporphyrin-III (16), and etioporphyrin-IV (17). 

If the eight peripheral substituents are made up of three kinds, for example two ethyls, two propionates and four methyls (with one methyl on each pyrrole subunit) then 15 isomers are possible, and these are related to the original primary type isomers as shown in Scheme 2. Further complications, many of which can be found in chlorophyll degradation products, lead to a third (larger) set of type isomers which can be directly related to those in Scheme 2. 

D-Methamphetamine, the AZ-methyl derivative of amphetamine, was first synthesized in 1919. Methamphetamine is available in the d- and l-forms. The D-form has reportedly greater central stimulant activity than the L-isomer, which has greater peripheral sympathomimetic activity. The D-form is the commonly abused form while the L-isomer is typically found in nonprescription inhalers as a decongestant. 

Scopolamine is levorotary to polarized light the racemic form, atroscine, which is often present in commercial scopolamine, acts only half as strongly on the peripheral organs, because in it the levorotary is mixed with the dextrorotary isomer, which is almost inactive. The cerebral action is equal, however, in the two forms. 

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