4624
K . BIEMANN,P BOMMER, A L BURLISGARIE, A K D \\ J ~ I c ~ I u R R . % Y
[CONTRIBUTION FROM THE
DEPARTMEST OF
CHEMISTRY, MASSACHCSETTS ISSTITL'TE OF
Yo1 h(i
TECHSOLOGY, CAhlBRIDCE 39, M A S S ]
High-Resolution Mass Spectra of Ajmaline and Related Alkaloids',2 BY K . RIEMANN,P. BORIRIER, A. L. BCRLINGASIE, A N D LV. J. ~ I C ~ I C R R A Y RECEIVED J L S E 11, 1964 T h e mass spectra of ajrnaline ( I ) and a series of derivatives, such as 21-deosy, l;-epi, l;-keto, 19,20-dehl-dro, and 2-epi analogs, as well as others ha\-ing additional substituents a t C-16 or in the benzene ring, have heen determined. The fragmentation processes, some of ~ l i i c hare very sensitive to subtle structural changes ( e . n . , epirnerization a t C-2), are discussed in t h e light of more precise d a t a ohtained with a douhlc-focusing mass spectrometer
As part of a systematic study of the mass spectra of alkaloids3 and during the course of the determination of the structure of cluebrachidined we determined the mass spectra of a series of compounds related to ajmaline ( I ) , the major alkaloid of liciuw\o(fia serpentinn Benth. The availability of a number of derivatives of this alkaloid5 such as 21-deoxy analogs, Ii-ketones (e.g., ajmalidine, V ) , 19,20-dehydro derivatives ( ~ . g . , tetraphyllicine, IV) as well as epimers a t the C-2, C-17, or C-21 position provided an interesting set of compounds possessing the same carbon skeleton but differing in rather subtle details which in some instances do and in others do not change the fragmentation of the molecule as shall be shown below. The earlier part of this study3 made use of conventional mass spectra obtained with a single focusing spectrometer and this work has more recently been augmented by the determination of the accurate masses of all ions produced from these compounds on electron impact using a high-resolution mass spectrometer of the Mattauch-Herzog type. These data permit a much more detailed and better supported interpretation than earlier studies of the mass spectra of alkaloids in which single-focusing instruments were employed. AS implied in previous brief communications on some of the aspects of this the mass spectra of ajmaline derivatives fall into three general groups, namely, those. that are similar to the mass spectrum of ajmaline (I, Fig. 1) itself, those t h a t possess a ITketone group and differ considerably in mass spectrometric behavior from ajnaline but are very similar to the spectrum of ajmalidine (TT),R and finally those which again differing in the stereochemistry a t C-2, greatly alters their fragmentation behavior as illustrated by the spectrum of quebrachidine (X). 4 The mass spectral characteristics of these three groups shall be outlined below along with proposals for the course of the fragmentation deduced from the highresolution mass spectra of these compounds. T h e mass spectrum of ajmaline ( I ) is plotted in Fig. 1 as recorded with a conventional single-focusing spectrometer except t h a t the elemental composition, deduced from accurate mass measurements with a high-resolution spectrometer, has been added for those peaks whose (1) P a p e r X X I I on t h e "Application oi 5lass Spcctrometsy t o S t r u c t u r e Problem." :2) P a p e r X X I : K . B i e m a n n , P B o m m e r , a n d I ) 51. I)esiderio, Teli'ahedroir L e l l n . s , No. 2 6 , 1726 (19641 ( 3 ) h I.. Burlingame, Ph.L). Thesis. 51 I . T . . 1962 (1) 11,G o r m a n , A I,, Burlingame, a n d K. Biemann. T c t ~ n h c d i . o i 1I . r l l e v s , No. 1, 39 (1968). ( 5 ) F o r leading references t o t h e s t r u c t u r e s of t h e c o m p o u n d s see h l . I;. B a r t l e t t . R . S k l a r , W I . T a y l o r , E. Schlittler, I
