Chemical examination of calabar beans / by Arthur H. Salway.

  • Salway, Arthur H. (Arthur Henry)
Date:
[1911?]
Catalogue details

Licence: In copyright

Credit: Chemical examination of calabar beans / by Arthur H. Salway. Source: Wellcome Collection.

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    CCXLII.—Chemical Examination of Calabar Beans. By Arthur Henry Salway. The socalled Calabar beans, the ripe seed of Physostigma veneno- sum, Balfour, have previously been the subject of several investi¬ gations, and their most important constituent—the alkaloid physostigmine or eserine—has long been recognised by most of the national Pharmacopoeias on account of its valuable medicinal properties. The first chemical examination of Calabar beans was conducted by Jobst and Hesse (Annctlen, 1864, 129, 115), who ascertained that their poisonous action is due to an alkaloid, which they designated physostigmine. This substance was obtained by them only as an amorphous, varnish-like mass, but a year later Vee (Jahresber., 1865r 456) succeeded in isolating the alkaloid in a crystalline state. The lash-mentioned investigator found that the alkaloid melted at 69°, and proposed for the crystalline base the name eserine. Jobst and Hesse, in a later investigation (Annalen, 1867, 141, 913), assigned to physostigmine the formula C15H2102N3, but still expressed doubt regarding its crystalline character, although it is now known that under suitable conditions the alkaloid, as stated by Vee (loc. cit.), can be obtained in the crystalline form. In the year 1876 Harnack and Witkowski (Arch, experim. Path., 1876, 401) indicated the presence of a second alkaloid in Calabar beans, for which they proposed the name calabarine. This substance was very indefinite in character, being chiefly distinguished by its tetanus-like effects on the living organism. Subsequent investiga¬ tions, notably that of Ehrenberg (Verh. Ges. Deut. JVaturf. Aertzte, 1893, II, 102), have shown that calabarine was in all probability a product of decomposition, and could not have pre-existed in the Calabar bean. It is evident, however, that besides physostigmine a very small proportion of other alkaloids is contained in the Calabar bean; thus, in the year 1888, a crystalline base, differing from physostigmine, was obtained by Bohringer & Sohne (Pharm. Post, 1888, 21, 663), and termed by them eseridine. This base was stated to melt at 132°, to be much less poisonous than physostig¬ mine, and on heating with dilute mineral acids to become converted into the latter alkaloid. Eseridine has been further examined by Eber (Pharm. Zeit., 1892, 37, 483), who assigned to it the formula C^H^OsNs, and it is thus seen to differ from physostigmine only in the elements of one molecule of water. Ehrenberg (loc. cit.) succeeded in isolating a third alkaloid from the Calabar bean. This substance, which is present in extremely