Asymmetric Nitrogen Atoms in Natural Products

Abstract

IT has been generally admitted that, although optical activity can be developed in compounds containing asymmetric atoms of carbon, nitrogen, phosphorus, arsenic, sulphur, selenium, tin, etc., as well as in “centro-asymmetric” compounds in which no asymmetric atom can be detected, all naturally-occurring compounds owe their optical activity to the presence of one or more asymmetric carbon atoms. It is, therefore, somewhat of a surprise to discover that the salts of nicotine contain an asymmetric nitrogen atom, in addition to the asymmetric carbon atom to which the free base owes its optical activity, since it was believed that the former type of asymmetric atom was only to be found in laboratory products. It is nevertheless clear, from the formulæ set out below, that the addition of a proton to the nitrogen atom of the pyrrolidine ring of the base does in fact convert this atom into a quaternary ammonium ion, which is linked to four different radicals, and must therefore be regarded as asymmetric, whatever opinion may be held as to the asymmetry of the tri-substituted ammonia from which it is derived.