Chromatographic Analysis of Alkaloids

Milan Popl, Jan Fahnrich, Vlastimil Tatar, Popl

• Publisher: CRC Press
• Year: 2018
• Print ISBN: 9780367834937
• eBook ISBN: 9781351460873
• Topic: Physical Sciences
• Subtopic: Chemistry
• Index: Chemistry

Beginning with classification, nomenclature, and structures, this reference discussesphysicochemical properties of alkaloids relevant to the chromatographic process.Chromatographic Analysis of Alkaloids explores the main experimental factors affectingthe separation and detection of alkaloids in gas (GC), liquid (LC), and thinlayer(1LC) chromatography ... illustrates separation conditions described in recentliterature ... provides, for a given compound, the GC, LC, and 1LC techniquesavailable within the same paragraph ... surveys, in tabular form, the methods forsample preparation for chromatographic analysis ... contains over 1,200 up-to-datereferences covering the majority of papers on the chromatography of alkaloids... and more.Serving as a rich resource of practical information, Chromatographic Analysis ofAlkaloids is essential reading for analytical, organic, natural products, and forensicchemists and biochemists, pharmacologists, and graduate-level students in thesedisciplines.

1

Classification of Alkaloids

The alkaloids, comprising over 5000 compounds of all structural types, belong to a large class of natural products. In this class the use of trivial names entirely dominates and systematic nomenclature is missing. The trivial names of alkaloids characteristically end with -ine. According to the definition (1), almost all alkaloids occur exclusively in plants and contain at least one nitrogen atom per molecule, which is basic in character and usually constitutes part of a heterocyclic system. However, some other natural products not belonging to the alkaloids meet this specification and, conversely, some well-known alkaloids do not fully comply. A few dozen alkaloids have been isolated from animals and in certain cases the same compound has been found in both plants and animals. Some neutral or weakly basic compounds are classified as alkaloid, e.g., colchicine (pK_b 12.35) in which the nitrogen is involved in an amide group. A newer definition (2) of alkaloids is much simpler: an alkaloid is a cyclic organic compound containing nitrogen in a negative oxidation state which is of limited distribution among living organisms. This definition can be supplemented by the statement that almost all alkaloids are toxic and the large majority of them have shown pharmacological activity.

The classification of alkaloids is a difficult task even for specialists in the field; therefore, in this book the alkaloids will be classified roughly according to the type of heterocyclic system which contains the nitrogen atom. These large groups are further divided into subgroups in accordance with botanical classification of plant species in which a certain type of alkaloid occurs, e.g., tobacco alkaloids, Amaryllidaceae alkaloids, Senecio alkaloids, and so on. Sometimes the name of the subgroup is derived from that of a well-known alkaloid, e.g., quinine, yohimbine, etc.

The brief review of the major alkaloid groups given in the following sections is drawn from the literature (3–5). Due to the large number and structural diversity of alkaloids, one cannot expect this review to be exhaustive.

I. PHENYLETHYLAMINE DERIVATIVES

This group of alkaloids, structurally based on 2-phenylethylamine C₈H₁₁N [1], is occasionally associated with the group of isoquinoline alkaloids by virtue of being biosynthetically related to tetrahydroisoquinoline C₉H₁₁N [2]. Structure [1] has been isolated from Accacia prominens as well as its N-methyl derivative. Among this group mescaline C₁₁H₁₇O₃N [3] as a drug of abuse is of greatest importance.

Mescaline has been found in extracts from the cactus Anhalonium lewinii in addition to N-methylmescaline C₁₂H₁₉O₃N and N-acetylmescaline C₁₃H₁₉O₄4N.

Some derivatives of phenylethylamine occur in plants as quaternary ammonium compounds, e.g., candicine C₁₁H₁₈ON⁺ [4], which has been found in the cactus Trichocereus candicans. A special subgroup is formed by ephedrine C₁₀H₁₅ON [5] and its derivatives. In the molecule of this base are two asymmetric carbon atoms, which means that ephedrine can create four optical antipodes and two racemates. In plants, e.g., Ephedra vulgaris, levorotatory ephedrine and dextrorotatory ψ-ephedrine have been found, which are not optical antipodes but diastereoisomers. Ephedrine is widely used in pharmaceutical preparations. In plant species ephedrine is accompanied by norephedrine C₉H₁₃ON (phenylpropanolamine) and N-methylephedrine C₁₁H₁₇ON.

To the ephedrine subgroup can be formally added colchicine C₂₂H₂₅O₆N and other alkaloids obtained from Colchicum autumnale in which nitrogen is not involved in a heterocyclic ring. Colchicine contains an amide group and is essentially a neutral compound.

II. PYRIDINE AND PIPERIDINE ALKALOIDS

These bases form a large group containing compounds with aromatic rings as well as dihydro and tetrahydro derivatives, and hexahydro derivatives (piperidines). The large majority of this group is formed by the subgroup of piperidine derivatives in which the tropane alkaloids are included.

A. Pyridine Alkaloids

The important tobacco alkaloids occur in plants of the Nicotiana genus. The well-known compound nicotine C₁₀H₁₄N₂ [6] contains pyridine and pyrrolidine rings. The isomer of nicotine is called anabasine C₁₀H₁₄N₂ [7] and has in its molecule a piperidine ring. The two optical isomers of tobacco nornicotine C₉H₁₂N₂ and nicotyrine C₁₀H₁₀N₂, can be prepared by the dehydrogenation of nicotine.

B. Dihydro- and Tetrahydropyridine Derivatives

The representative compound with a dihydropyridine ring is ricinine C₈H₈O₂N₂ [8], which is found in Ricinus communis. Alkaloids based on tetrahydropyridine structure have been isolated from Areca catechu. They are arecaidine C₇H₁₁O₂N [9], its nor derivative guvacine C₆H₉O₂N, and its methyl ester arecoline C₈H₁₃O₂N.

C. Piperidine Alkal...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Preface
• Chapter 1. Classification of Alkaloids
• Chapter 2. Properties of Alkaloids Relevant to Chromatography
• Chapter 3. Chromatography
• Chapter 4. Gas Chromatography
• Chapter 5. Liquid Chromatography
• Chapter 6. Thin-Layer Chromatography
• Chapter 7. Applications
• Chapter 8. Conclusion
• Index