Spectral methods, alkaloid structures

Pavines and isopavines are two relatively small subgroups of the isoquinoline alkaloids, being represented by 22 and 11 compounds, respectively. Few new examples have been reported in the last decade, which stands in contrast to the rapid increase in the number of known natural compounds in recent years as a consequence of improved isolation techniques and spectral methods of structure elucidation. 

Several alkaloids (130-142) were isolated from plants of the genera Cadia, Calpurnia, Sarothamnus, and Genista. They are believed to be ethers and esters of hydroxylupanine derivatives (159-178). Alkaloid esters on hydrolysis gave the respective organic acids and hydroxylupanines. The structures of these alkaloids have been established mainly by spectral methods. 

Bisbenzylisoquinoline alkaloids. Comprehensive tabulation of literature for 1978-1981 (Chemical Abstracts Volumes 88-95), with 164 references. Covers structure revisions, additional (mainly spectral) data on known alkaloids, new sources of known alkaloids, structures, properties, summarized confirmatory reactions of new alkaloids, and biosynthetic evidence. Alkaloids are tabulated by botanical sources and pharmacological activity. A section on methods (CD, luminescence spectra, specific rotation, TLC) is included. 

Argentine (9) and argentamine (10) are two new alkaloids whose structures were determined by spectral methods (4). 

The alkaloid heptaphylline (C13H1703N) was shown to have structure 62 by means of spectral methods and confirmation by a synthesis. Girinimbine was also present in this plant (33). 

Three imidazole alkaloids have been isolated from this plant. Their structures were ascertained largely by spectral methods and confirmed wholly or partly by limited chemical reactions anantine (C15H15ON3 mp 204° [a]D —549 W-acetyl, mp 99°) (69) cynometrine... 

In addition to the known alkaloids from this plant the trunk bark yielded the new hernandonine (C18H905N mp > 280°) whose structure (109) was determined largely by spectral methods and confirmed by its synthesis from N-methylhernovine by known reactions (88). 

The structure of the alkaloid propyleine (C13H21N amorphous levorotatory) (156) from this beetle was determined by spectral methods supplemented by chemical methods. It is the dehydro derivative of coccinellin (143) into which it was converted (144). 

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. 

All alkaloids of the group have methoxyl groups at C-17 and C-21 and the same skeleton. The structure of these alkaloids was established by a combination of chemical and spectral methods. 

In this chapter, alkaloids isolated from Strychnos species are presented in tabular form (see Table II). Most recent papers on these subjects simply describe the structures of new alkaloids as determined primarily by spectral methods. Therefore, detailed description concerning structure elucidation of individual alkaloids seems unnecessary. Coverage of the literature starts from around 1965. In line with this principle, the Strychnos alkaloids tabulated by M. Hesse (7,8) are included only when they were reported to be newly found in other species of Strychnos. Thus,... 

With the aid of the above structural revision of chondrocurine and mass and n.m.r. spectral analysis, the structure of the curine-type alkaloid chondrofoline (288 R = H) from Chondrodendron platyphyllum has been established.260 A simple method for the preparation of the C(4")-trideuteriomethoxy-compound (288 R = CD3) was also described. 

Since last year s Specialist Report, the emphasis in the di terpenoid alkaloid field has focused on structure determination, both by X-ray crystallography and by chemical and spectral methods. Some interesting synthetic approaches to diterpenoid alkaloids have also been reported. The total volume of work on diterpenoid alkaloids reported this year, however, is much less than in Chapter 16 of last year s Report, which covered a longer period and was intended to give a background to the subject. 

This alkaloid was isolated from Heimia salicifolia Link et Otto and its structure (66) was elucidated by spectral methods and by its reduction to decodine in which the cyclic double bond of 66 is reduced 80). 

In addition to the quinolylimidazole alkaloids previously isolated a reinvestigation served to reveal the presence of three new alkaloids of the same general type. Spectral methods were the source of most of the structural information of these bases but chemical transformations and degradations proved decisive in distinguishing between alternatives. 

The new alkaloid, peganidine (Ci HigOaNa mp 189° [ajp 0° oxime, mp 85° semicarbazone, mp 204°) from this plant has structure 165. Spectral methods were employed in the structural elucidation 196). Also found were dioxypeganine 197) and a new alkaloid, pega-mine, whose structure (166) was determined by spectral methods 198). 

Some earlier errors regarding this alkaloid have been corrected. It forms a hydrate hydrochloride (C23H33O7N HCl HgO) which on reaction with aqueous potassium carbonate gave stemonine and a neutral oil which was identified as 4-hydroxy-3-methoxy-2-methyl crotonolactone (178). In view of the known structure of stemonine (179) the structure of protostemonine is given as either 180 or 181. The chief tools in this work were spectral methods (212a). 

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). 

In addition to the previously known carnegine this plant yielded gigantine, C13H19O3N (mp 152° [a] + 27°) which was shown, mostly by exhaustive spectral methods, to have structure XXVII (27). This alkaloid and macromerine along with berberastine are a group of bases having a benzylic hydroxyl reminiscent of that in adrenaline and ephedrine (41). 

The new alkaloid, evoprenine, C20H21O4N (mp 143°) was shown to have structure LXIV by spectral methods and by a synthesis from evoxanthine... 

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

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. 

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