Tetrahydro 3-Carboline and Related Alkaloids

The identification of alkaloids of this type has been greatly facilitated by the introduction of mass spectrometry (165,162,163). By examination of a large number of derivatives, the breakdown pattern has been established, the principal peaks being represented by the fragments v and w which are formed by a cyclic transfer of electrons in ring D 

The structures assigned to the fragments observed are based on the following evidence (165, 171). 

Fifty per cent of the M-l peak is found at M-2 in the spectra of 3-deu-terioyohimbine (CCCVII, prepared by NaBD4 reduction of 3,4-dehydro-yohimbine perchlorate) and of 3,5,6-trideuterioajmalicine (CCCIX, prepared by NaBD4 reduction of serpentine hydrochloride), so that one-half of the hydrogen lost in the formation of this peak comes from C-3 or, in the case of ajmalicine, from C-3 and C-6. 

These four peaks remain invariable at m/e 170, 169, 184, and 156 respectively when alterations are made in ring E as in the series, CCXCV, CCCX, CCCXI, CCCXII, and CCCXIII, and they do. not therefore contain atoms from this ring. The addition of substituents at positions 1,3,10, and 11 results in a corresponding increment in the mass of these fragments as is seen in the spectra of CCCXIV, CCCXV, and CCCVII (Table V). The importance of these peaks is explained by the ready cleavage of the allylically activated 3,14 bond. 

Peak v, already shown to contain the indole residue, contains in addition carbon atoms 3, 5, and 6, for in the spectrum of 3,5,6-trideuterioajmalicine (CCCIX) all three deuterium atoms are retained in this fragment. In the spectrum of 3,14-dideuterioajmalicine (CCCVIII), prepared from serpentine by the successive action of NaBH4, HC1, and NaBD4, however, only one deuterium atom is retained in v which therefore does not contain C-14. Fragment w is derived from v by loss of one hydrogen from either C-5 or C-6 and this is shown by the fact that in the spectrum of 3,5,6-trideuterioajmalicine (CCCIX) w is split into two peaks, one in which one, and one in which two deuterium atoms have been retained. 

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