CHAPTER I - ISOLATION AND CHARACTERIZATION OF INDOLE ALKALOIDS

Abstract

Publisher Summary This chapter discusses the isolation and characterization of indole alkaloids. Many precipitation and chromogenic methods were developed by classical chemist for the isolation of alkaloids. They either depended on the water insolubility and color of complex acid salts or the generation of characteristic colors with oxidizing agents under defined conditions. For indole alkaloids, some color reactions are specific to a particular indolic system and in a very crude mixture, such a test is often more useful than attempting to measure and interpret an ultraviolet absorption spectrum. Once the crude alkaloids have been obtained, separation methods are applied that take advantage of previous experience and modern methodology, such as column, partition, or ion exchange chromatography; countercurrent distribution; and the like. The results of the fractionation can be followed by all or as many of the physical methods as need be brought to bear to the problem. The isolated pure base can be characterized via its melting point, via its optical rotation, via its ultimate analyses, and by the formation of derivatives. The ultraviolet absorption spectrum defines the chromophoric moiety and the infrared spectrum, besides fingerprinting the molecule by its wealth of bands, detects various functionalities, in particular carbonyl groups and hydrogen attached to nitrogen or oxygen. Nuclear magnetic resonance spectroscopy yields information from which the proton topography can be deduced. There is also the mass spectrum; the interpretation of whose line-rich spectrum often allows the entire structure of the alkaloid to be deduced. With the structure of the indole alkaloid largely defined by the use of the above methods, the chemist can operate more meaningfully with small amounts of material to complete the structure proof.