Dihydro- 3-carboline anhydro-bases

Formation of a quinonoid carboline-type anhydro-base requires loss of resonance stabilization of the indole moiety. In the carboline anhydro-bases this is counterbalanced by the preservation of a 677 system in the hetero ring. No such balancing factor is present in the case of 3,4-dihydro-j3-carboline derivatives. Formation of the exocyclic anhydro-base in the latter case preserves benzenoid resonance. It is noteworthy that in the two cases where formation of a carboUne-type anhydro-base was reported in dihydro derivatives additional aromatic conjugation is present. 

This dimeric formulation also accounts for the thermal disproportionation of the compound into a mixture of 2-methyl-l,2,3,4-tetrahydro-jS-carbohne and 2-methyl-jS-carboline anhydro-base. Normal pseudobase formation (453 R = CHs ) takes place in the case of 9-methyl-3,4-dihydro-j3-carbohne methiodide (452 R = CHg). Neither the dimeric anhydro-base nor the -methyl pseudo-base undergo a base-catalyzed disproportionation reaction to give the 1,2,3,4-tetrahydro-and the l-oxo-l,2,3,4-tetrahydro-jS-carboline in a manner analogous... 

The dihydro-j8-carboliniuin salt 450 has been reported to form a pseudobase (451) on treatment with alkali. It is of interest that the pK value for this compoundi - as found to be 11.7, i.e., of the same order of magnitude as those of the jS-carboline anhydro-bases. 

Anhydro-bases derived from 3,4-dihydro-)3-carboline derivatives have received much less attention than those of the carboline series. 

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). 

Alkylation of the anhydro-bases derived from 3,4-dihydro-jS-carboline and l-methyl-3,4-dihydro-)5-carbohne takes place at the pyr-N and is accompanied by ring cleavage. It was beheved that alkylation of the anhydro-bases derived from 7-methoxy-l-methyl-3,4-dihydro-jS-carboline alkiodides occurred at the pyr-N to give quaternary salts of type 458. It has now been shown, however, that methylation of the anhydro-base 438b (R = CH3) actually gives the... 

Ultraviolet spectra of a l,2-dihydro-y-carboline derivative and of a number of quaternary l,2-benz-3,4-dihydro-j8-carbolinium derivatives and of the anhydro-bases derived from them have been... 

Ultraviolet spectra of a 1,2-dihydro-y-carboline derivative and of a number of quaternary l,2-benz-3,4-dihydro-j8-carbolinium derivatives and of the anhydro-bases derived from them have been recorded. It is noteworthy that introduction of a 6-hydroxyl group does not affect the spectrum of the l,2-benz-3,4-dihydro-j8-carbolinium ion, whereas introduction of a 7-methoxyl group leads to a bathochromic shift of 20... 

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