Alkaloid structures spectral methods, study

Alkaloid structures forensic chemistry of, 32, 1 (1988) spectral methods, study, 24,287 (1985) unknown structure... 

The literature dealing with alkaloids shows no obvious signs of abatement. The classic methods of the organic chemist employed in structural determinations have evolved into spectral methods, and chemical reactions are involved largely in confirmatory and periferal studies. Inasmuch as the spectral methods have become largely standardized we incline to limit the details in these volumes. 

If this interaction is not possible, the shift does not occur.37 The ultraviolet spectra have been studied in connection with the structure of aliphatic 3 and cyclic enamines,1, 28,37, 43 cis-trans isomerism about their double bond,27 and the structures of enamines with additional functional groups.17, 20, 31,32 Ultraviolet spectral data have been used also as a general method to determine the structure of alkaloids and in the study of some reaction mechanisms. 

Alkaloid A4 (C20N24O2N2 mp 154° [ ] +131°) from this plant was shown to be identical with that already described (219). Its structure (189) was determined by spectral methods, and finally by an X-ray study (220). 

The classical example of this type of reaction is the v. Braun method of degradation, by which a secondary amine can be transformed into a primary amine, and finally into ammonia, via the imidoyl chloride intermediates. This reaction has been used for the structure elucidation of alkaloids. Although degradative studies are not conducted to any extent today due to the convenience of spectral methods, the v. Braun elimination is still used in organic synthesis to prepare nitriles as well as alkyl halides. 

The structure of HRP-I has been identified as an Fe(IV) porphyrin -ir-cation radical by a variety of spectroscopic methods (71-74). The oxidized forms of HRP present differences in their visible absorption spectra (75-77). These distinct spectral characteristics of HRP have made this a very useful redox protein for studying one-electron transfers in alkaloid reactions. An example is illustrated in Fig. 2 where the one-electron oxidation of vindoline is followed by observing the oxidation of native HRP (curve A) with equimolar H202 to HRP-compound I (curve B). Addition of vindoline to the reaction mixture yields the absorption spectrum of HRP-compound II (curve C) (78). This methodology can yield useful information on the stoichiometry and kinetics of electron transfer from an alkaloid substrate to HRP. Several excellent reviews on the properties, mechanism, and oxidation states of peroxidases have been published (79-81). 

The main alkaloid, porantherine (C15H23N mp 36-40° [a]D +29°) was shown, by X-ray analysis, to have structure 153. Other spectral studies are consonant therewith (140). Two further alkaloids have been reported and their structures have also been elucidated by X-ray methods. Poranthericine (C15H27ON oil [a]D —20° B.HBr, mp 308°) has structure 154. Its acetyl derivatives (oil) was also isolated from the plant. Porantheridine (C15H270N oil [a]D -26° B.HBr, mp 165-166° [a]D —19°) has structure 155 (140-142). 

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