Ephedrine is an alkaloid that is present in various forms of the ephedrine family, and which is still extracted from Ephedra sinica and Ephedra equisetina. Because of the presence of two asymmetric atoms, there are four isomeric forms. Pseudoepinephrine (d-isoephrine) is a stereoisomer with pharmacological action that differs slightly from ephedrine. The pharmacological action of ephedrine is typical of noncatecholamine sympathomimetics of mixed action. It stimulates both a- and ¡-adrenoreceptors, and simultaneously causes a release of norepinephrine from synaptic neurons. Its vasoconstrictive ability is approximately 100 times weaker than that of epinephrine; however, the duration of action is approximately 10 times longer. It is much less toxic than epinephrine, which allows it to be used widely in medicine.
It is mainly used for bronchial asthma, allergic illnesses, as an antiedemic for mucous membranes in rhinitis, and also as a drug to increase blood pressure during surgical interventions. It is used locally in ophthalmology as a vasoconstricting agent for dilating pupils. Synonyms of this drug are epipen, ephedrol, manadrin, calcidrin, and others.
Phenylpropanolamine: Phenylpropanolamine, d,l-erythro-1-phenyl-2-methylamino-propanol-1 (11.3.7), is synthesized from propiophenone by nitrosation into an isonitroso derivative (11.3.6). Reduction of this by hydrogen in hydrochloric acid while simultaneously using two catalysts, palladium on carbon and platinum on carbon, gives norephedrine (11.3.7) [56-59].
O CH3NO2 O H2/Pd-C + Pt-C ; HCI NH2 4 ^-C-CH2-CH3 -i j^C-IC-C^ -^ ^ CH _CH _ch3
The pharmacological action of phenylpropanolamine is similar to the action of ephedrine. This sympathomimetic can temporarily elevate blood pressure, and it is used for the same indications as is ephedrine, which is primarily in combination with other drugs for catarrhal illnesses. In addition, it possesses weak central-stimulatory and anorectic action. The primary synonym is norephedrine.
Metaraminol: Metaraminol, l-1-(3-hydroxyphenyl)-2-aminopropan-1-ol (11.3.11), is synthesized in two ways. The first way is synthetic, and it is from 3-hydroxypropiophenone. The hydroxyl group is protected by alkylation with benzyl chloride, giving 3-benzy-loxypropiophenone (11.3.8). Upon reaction with butylnitrite, it undergoes nitrosation into the isonitrosoketone (11.3.9), which by reduction using hydrogen over Raney nickel turns into 1-(3-benzyloxyphenyl)-2-aminopropan-1-ol (11.3.10), the protecting benzyl group is removed by reduction using hydrogen over palladium catalyst, to give racemic metaraminol (11.3.11). The desired l-isomer is isolated with the help of (+)- tartaric acid [60,61].
O C6H5CH2O C6H5CH2O
)=\ O C6H5CH2C )=\ O C4H9NO2 ¿ \ C C CH ^^-C-CH2-CH3 -- -^ jj"™3
The second way is semisynthetic, consisting of fermentation of d-glucose in the presence of 3-acetoxybenzaldehyde, which forms (-)-1-hydroxy-1-(3-hydroxyphenyl)-acetone (11.3.12), the carbonyl group of which is reduced by hydrogen over a palladium catalyst in the presence of ammonia, giving metaraminol (11.3.11) [62-65].
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