Carbolinium salts, anhydro-bases

Anhydro-bases derived from quaternary )S-carbolinium salts are reduced to p /r-A-substituted-l,2,3,4-tetrahydro-j8-carboline derivatives on hydrogenation over Adams catalyst in methanol solution made alkaline to ensure the presence of anhydro-base. ... 

Further alkylation of the anhydro-bases derived, by treatment with strong base, from quaternary 1-alkyl-a-, 2-alkyl-j8-, 2-alkyl-y-, and l-alkyl-8-carbolinium salts takes place at the indole nitrogen which in the anhydro-bases is a center of high electron density (see Section VI). 

When a jo /r-A-alkylcarbolinium salt, unsubstituted at the ind-N atom, is treated with strong alkali, a yellow to deep orange, strongly basic solid separates. Although such products almost invariably give poor microanalytical values they can be shown to be derived from the quaternary hydroxide by loss of a molecule of water—hence the name anhydro-bases or anhydronium bases.All four carbolines form anhydro-bases e.g., j9 /r-A-methyl-j8-carbolinium iodide (419) gives 420. Most of the evidence bearing on the structures of these bases has been summarized, and discussion will therefore be limited to a few of the recent aspects of the chemistry of these compounds. 

That the ind-N atom in the anhydro-bases is the basic center is also obvious from a consideration of the ultraviolet absorption spectra of the anhydro-bases. In aqueous 0.1 A hydrochloric acid as well as in neutral alcoholic solutions each carboline anhydro-base gives rise to an ultraviolet absorption spectrum identical with that of the parent carbolinium salt. In alkaline solutions (pH above 11.5 in the case of the... 

The third structural possibility, the formulation of the compounds as pseudo-bases (445) was eliminated in the case of the anhydro-bases derived from p /r-iV -alkyl-l-methyl-3,4-dihydro-j8-carbolinium salts on the basis of their ultraviolet absorption spectra. A structure such as 445 demands indole-type absorption (A jax 280 mp) which was not encountered in the spectra of the anhydro-bases under discussion. This is in accord with general experience. Pseudo-bases are generally found only when dehydration to anhydro-bases is structurally impossible Indole-type absorption was indeed found in the case of the product obtained by treatment of 3,4-dihydro-)3-carboline methiodide (452 R = H) with alkali.In acid solution this compound gave the expected absorption (A jax 355 mp). In alkaline solution, however, an indole-type absorption (A jax 285 mp) was observed. On this basis formulation of the product as a derivative of 2-formylindole (454) ( max 315 mp) was rejected. Although the indole-type absorption is in accord with the pseudo-base structure 453 (R = H), the elemental analysis and molecular weight were not compatible with this formulation and the product was regarded as a dimeric anhydro-base (455). 

The third structural possibility, the formulation of the compounds as pseudo-bases (445) was eliminated in the case of the anhydro-bases derived from yr-JV-alkyl-l-methyl-3,4-dihydro-jS-carbolinium salts on the basis of their ultraviolet absorption spectra. A structure such as 445 demands indole-type absorption 280 mfi) which was not... 

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