Proton magnetic resonance alkaloids

Physical and spectral properties of samandarine alkaloids are presented in Table II. Mass spectra of various samandarine alkaloids and derivatives have been presented 38-43). Fragments of C4H8NO (m/z 86) and C4H7NO+ (m/z 85) are typical of oxazolidine-containing samandarine alkaloids. Infrared spectra of various samandarine alkaloids have been published 33,34,43-46 and references therein). Proton magnetic resonance spectra for samandarone, samandenone, and cycloneosamandione have been presented 38,40,41). Samandarine, samandarone, and... 

Scheme 1. Proton magnetic resonance data for typical quinoline alkaloids. In CDCl3 unless stated otherwise. Figures refer to values-, s, singlet-, d, doubler, t, triplet q, quartet and m, multiplet.

Pmr. Proton magnetic resonance (pmr) spectroscopy provides a reliable analysis of pyrrolizidine alkaloids if sufficient quantities of alkaloid 1 mg) are present The amount of total alkaloid is estimated by comparison of the area of the vinyl proton (H2) signal (present in all 1,2-unsaturated and seco alkaloids) with that of an added internal standard ( dinitrobenzene)... 

Fig. 5. Proton magnetic resonance spectra (100 MHz) for batrachotoxin class alkaloids and assignments. Chemical shifts in ppm (5) for deuterochloroform with a tetramethylsilane standard. Assignments A pyrrole NH B pyrrole 5-H C olefinic proton at C-7 D oleflnic proton at C-16 proton at C-20 FI4-OCH2 and proton at C-11 G one proton at C-15, the other appears at 6 2.3 methylene protons at C-18 / pyrrole 2-CH3 T and / pyrrole 2-CH2CH3 / NCH3 K pyrrole 4-CH3 L 2I-CH3 M I9-CH3 (see Fig. 4)...

Compound I (mol. wt. 195, C13H25N) was saturated and lost a — C4H9 fragment to yield a base peak at m/z 138 in its mass spectrum. The data, including proton magnetic resonance spectrum, were compatible with a structural formulation of a 2-n-butyl-ci5 -decahydroquinoline, but a carbon-13 magnetic resonance spectrum was not obtained and this compound is tabulated for the present as 195 C under Other Alkaloids. 

A synthesis of a 2-n-propyl-cw-decahydroquinolin-5a-ol has been reported (Scheme XX) (727). This compound is of interest since it is related to structures previously and tentatively proposed for certain trace alkaloids of a so-called hydroxypumiliotoxin-C class (80). The mass spectrum was as follows m/z 197 (7) 154 (100) 136 (11) 111 (5) 72 (12). Infrared and proton magnetic resonance data were reported (727). The synthesis of the corresponding 2-n-propyl-c/.s-dehydroquinoline was reported in the early part of this century (262). 

One other pyridine alkaloid has been detected in dendrobatid frogs. The structure of this minor alkaloid, noranabasamine (XIII), was established by proton and carbon-13 magnetic resonance spectroscopy (14). The ultraviolet spectrum was as follows X ,ax (CH3OH) 244 nm, e 11,000, 275 nm, e 10,000. The optical rotation, [a]o, was -14.4° (CH3OH). Anabasamine, a plant alkaloid, also is levorotatory, but it is unknown whether noranabasamine, now given a code number 239J, has the same 2S configuration. 

There follows a discussion of proton nuclear magnetic resonance ( H NMR), carbon nuclear magnetic resonance ( C NMR), and mass spectrometry (MS) of the Narcissus alkaloids. A list of the different Narcissus alkaloids, their spectroscopic properties, and literature with the most recent spectroscopic data is given in Table X. 

Elucidation of the structures of the first group of alkaloids was slow until the advent of commercial recording ultraviolet and infrared spectrometers allowed the first major break through. We are presently witnessing a second revolution in the conduct of the art brought about by the availability of protons mappers (nuclear magnetic resonance machines) and mass spectrometers. The application, however, of the greatest ultimate promise is structure determination by means of the interpretation of X-ray diffraction data. 

Bumamicine. This natural constituent isolated in trace quantities from Hmteria eburnea is included here because of its obvious relationship to corynantheol and because it represents a good example of the use of mass spectrometry in structure deduction. Bumamicine had an ultraviolet absorption maximum typical of a 2-acylindole which changed to that of a typical indole upon either sodium borohydride reduction or solution in acid. After the latter experiment the original chromophore was regenerated in basic solution. From the nuclear magnetic resonance spectrum the four aromatic protons, the ethylidene and the N-methyl were identifiable. The recovered alkaloid upon acetylation had an ultraviolet and nuclear magnetic resonance spectrum consistent for an ind N,0-diacetate (probably primary). 

Recently, two additional batrachotoxin class alkaloids were isolated as minor constituents from skin extracts of Phyllobates terribilis. Mass spectra and proton and carbon-13 magnetic resonance spectra allowed assignment of structures as 4p-hydroxybatrachotoxin and 4P-hydroxyhomobatracho-toxin 254). 

Some of these compounds have been isolated in sufficient quantities for partial characterization by nuclear magnetic resonance spectroscopy. These include three trace compounds designated I, II and III which were isolated from extracts of some 3200 skins of Dendrobates histrionicus (86). All three compounds were bicyclic and based on the mass spectra and proton resonance spectra were proposed to be members of the pumiliotoxin-C class (cw-decahydroquinolines) of alkaloids. 

Such a protocol has been used to characterize a large number of dendrobatid alkaloids. Two additional alkaloids of the histrionicotoxin class were detected and characterized. These were histrionicotoxins 235 A and 259 (see Fig. 13). The structure of histrionicotoxin 259 has been confirmed by proton and carbon-13 magnetic resonance spectroscopy (255). Histrionicotoxins as a class are characterized by a major fragment ion (CsHioN) at m/z 96. All form O-acetyl derivatives and all of the eleven... 

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