Fraser proved that by substitution of molecules in certain compounds a stimulant could be converted into a sedative action; thus by the addition of the methyl group CH 2 to the molecule of strychnine, thebaine or brucine, the tetanizing action of these drugs is converted into a paralysing action.
(4) Isoquinoline group. The opium alkaloids: morphine, codeine, thebaine, papaverine, narcotine, narceine, &c.; and the complicated substances hydrastine and berberine.
Thebaine, another alkaloid, was discovered by Thiboumery in 1835; whilst, in 1848, Merck isolated papaverine from commercial narcotine.
Cotarnine IV.Narceine The chemistry of morphine, codeine and thebaine is exceedingly complicated, and the literature enormous.
That these alkaloids are closely related may be suspected from their empirical formulae, viz.morphine = C17H19N03, codeine = C18H21N03, thebaine = C19H21N03.
Thebenine and morphothebaine, from both codeine and thebaine, thereby establishing their connexion.
Thebaine forms silvery plates, melting at 193°.
Thebaine is not so used, but is an important and sometimes very dangerous constituent of the various opium preparations, which are still largely employed, despite the complexity and inconstant composition of the drug.
Of the other alkaloids narceine is hypnotic, like morphine and codeine, whilst thebaine, papaverine and narcotine have an action which resembles that of strychnine, and is, generally speaking, undesirable or dangerous if at all well marked.
The chief difference between the action of opium and morphine is due to the presence in the former of thebaine, which readily affects the more irritable spinal cord of very young children.
The alkaloid thebaine may here be referred to, as it is not used separately in medicine.
Crum Brown and Fraser of Edinburgh showed that, whilst thebaine acts like strychnine, methyl and ethyl thebaine act like curara, paralysing the terminals of motor nerves.
At present we say of such a substance as thebaine, " it acts on the anterior cornua of grey matter in the spinal cord," but why on them and not elsewhere we do not know.
In morphine, on the higher animals at least, the narcotic action is very marked, the tetanizing action slightly so; while in thebaine there is little narcotic effect, but a tetanizing action like that of strychnine.