Analytical Determination of Nicotine and Related Compounds and their Metabolites

J.W. Gorrod, P. Jacob III, J.W. Gorrod, P. Jacob III

• Editorial: Elsevier Science
• Año: 1999
• ISBN:
  9780080525518
• Categoría: Ciencias físicas
• Categoría: Química analítica

This book provides for the first time a single comprehensive source of information on the analytical chemistry of nicotine and related alkaloids. The editors have brought together scientists from academia and the tobacco industry to describe the state-of-the-art of the chemistry and analytical methods for measurement of nicotine. Both the scope and detail of the book are impressive. Chapters describe the history, pharmacology and toxicology of nicotine, the biosynthesis of nicotine and other alkaloids in the tobacco plant, the general chemistry of nicotine and the analytical methodologies that have been used to measure nicotine and related alkaloids in biological specimens, in tobacco and pharmaceutical products and in tobacco smoke. There is also a comprehensive review of the chemistry and toxicology of nicotine-derived nitrosamines, an important class of tobacco carcinogens.

Chapter 1

Pharmacological significance of nicotine

Edward F. Domino, Department of Pharmacology, University of Michigan, Ann Arbor, MI 48109-0632, USA

I. INTRODUCTION

It is generally acknowledged that nicotine is the principal alkaloid that accounts for the widespread human use of tobacco products throughout the world. In addition to its importance in tobacco products, nicotine is used as an insecticide for agricultural and horticultural purposes. Nicotine alone as a chemical has a commercial and environmental impact: in addition, its chemical and pharmacological significance is of fundamental biological importance.

II. HISTORICAL ASPECTS

Jean Nicot, a French ambassador 449 years ago, in 1550 sent tobacco and seeds to Paris from Portugal and, thus, introduced the French to tobacco from the New World. Nicotiana tabacum was indigenous to tropical America; the dried leaves were smoked by native Indians at the time Columbus discovered the New World. The dried leaves were called tabacum which was then used by the Spanish and Portuguese, and subsequently by the French and Italians. The English obtained their tobacco directly from America. It did not take long for the rest of the world to become involved with tobacco use and abuse. Crude aqueous extracts of tobacco were used by native tropical American populations, but by 1571 such extracts became more generally available.

The history of the chemical identification of nicotine has been well described (see [1, 2]). Cerioli in 1807 and Vauquelin in 1808 isolated the ‘essential oil’ or ‘essence of tobacco’. In 1828, Posselt and Reimann isolated nicotine from tobacco and in 1843 Melsens described its chemical empirical formula. Pictet and Crepieux synthesized nicotine in 1893 and in 1904 Pictet and Rotschy described the chemical isomerism of nicotine. Only 21 years ago, in 1978, Pitner et al. identified the spacial orientation of natural (S)-nicotine, herein called nicotine.

The experimental use of nicotine contributed substantially to our knowledge of physiology. Langley and Dickenson [3, 4] noted that large concentrations of nicotine blocked autonomic ganglia, proving that autonomic nerves synapse in ganglia. Langley’s continued use of nicotine as a pharmacological tool greatly enlarged our knowledge of neuronal cholinergic synapses [5]. Heymans and colleagues showed that nicotine stimulates respiration via chemoreceptors in the carotid and aortic bodies associated with the carotid sinus and aortic arch [6]. The only central nervous system synapse in the spinal cord shown to be activated via the nicotinic actions of acetylcholine is the Golgi recurrent collateral-Renshaw cell synapse [7–11].

III. OCCURRENCE IN NATURE (see also Chapter 2)

Nicotine and related alkaloids are found in genus Nicotiana plants. Nicotiana tabacum is cultivated throughout the world for preparation of cigars, cigarettes, pipe and chewing tobacco. Nicotine usually constitutes about 2–8% of the dry weight of the cured leaf, although a much larger range exists in some Nicotiana plants. Other related alkaloids, including anabasine, anatabine, and nornicotine are also present, usually in much lower amounts. There are different relative amounts of all of these alkaloids in various Nicotiana species. The leaf content of nornicotine in some species is as high as 15–20% of the nicotine content. The chemical reviews on the alkaloids of tobacco by Jackson [12] and Pailer [13] are especially useful sources of more information. In other species such as N. glauca (tree tobacco), the main alkaloid is anabasine rather than nicotine. Interestingly, anabasine has been found in the marine worm Amphiporus and the ant Aphaenogaster. Other species of plants besides Nicotiana contain nicotine including Duboisia, Equisetum (horsetails), Lycopersicum (tomatoes), Lycopodium (club mosses), Sedum (succulent plants) and Solanum (potatoes). Therefore, it is not unexpected that trace amounts of nicotine are present in some edible human foods [14–18]. This is of interest in establishing threshold levels in human fluids of second hand tobacco smoke exposure. Surprisingly, this area of research has not been pursued, in part because of a lack of interest by granting agencies. Commercial nicotine is a byproduct of the tobacco industry. By adding lime or caustic soda to a filtered, concentrated aqueous extract of tobacco plant parts, the alkaloid can be isolated with either an organic solvent or by steam distillation. The addition of a chemical drying agent such as potash and subsequent fractional distillation further purifies nicotine.

IV. CHEMISTRY (see also Chapters 4 and 5)

The chemical characteristics of nicotine are well known [19]. Pure nicotine is a colorless liquid with a characteristic acrimonious odor. Nicotine boils at 246–247°C. On exposure to air and light, or even on standing in the dark in a sealed bottle, over time the colorless or pale yellow oily liquid becomes the brownish color of stored nicotine. Brown colored nicotine is as toxic as pure colorless or pale yellow nicotine. Nicotine is known chemically as 3-(1-methyl-2-pyrrolidinyl)pyridine; 1-methyl-2-(3-pyridyl)pyrrolidine; or β-pyridyl-α-N-methylpyrrolidine. Its empirical formula is C₁₀H₁₄N₂. Its molecular weight is 162.23; C 74.03%, H 8.70%, N 17.27%. Its density d²⁰₄ is 1.0097. Pure nicotine has a specific rotation [α]²⁵_D = −169°. When (S)-nicotine is boiled at 250°C with potassium tertiary butoxide, it racemizes. Therefore, nicotine can exist either as the (S)- or (R)-form. In this chapter, the natural (S) form is referred to as nicotine unless otherwise noted. After the absolute configuration of hydroxyproline and related compounds was determined, Hudson and Neuberger suggested that natural nicotine be designated as Ls-nicotine because the COOH group of N-methyl-Ls-proline can be replaced with a pyridine group [20]. The two isomers of nicotine are important in understanding its molecular pharmacology; they were used in the historical accumulation of evidence of cholinergic receptive substances, i.e., cholinergic nicotinic receptors.

A key chemical concept that determines nicotine’s absorption, excretion, pharmacology and toxicology is that its charged and uncharged forms are pH dependent. Nicotine is dibasic because of its pyrrolidine (pKa=7.84) and pyridine nitrogens (pKa=3.04) at 15°C. At a pH of 7.4 and a temperature of 37°C about 69% of the pyrrolidine nitrogen is ionized or positively charged, whereas the pyridine nitrogen exists in an unionized form [21]. Thus, the pH of a nicotine solution dramatically alters its protonated state. Uncharged organic bases are lipophilic, whereas charged organic bases are hydrophilic. Nicotine at pH 7.4 exists in both forms; one diffuses through lipoprotein membranes, the other does not. Nicotine, like other alkaloids with similar pKas, exists with a ratio of charged to uncharged forms of about 2 to 1 at pH 7.4. This chemical fact permits nicotine to have important biological actions.

V. TOXICOLOGY

The symptoms of nicotine poisoning are similar to those of tobacco poisoning. The naive tobacco smoker who overindulges experiences a strange feeling which soon progresses to increased salivation, nausea, and vomiting. Cardiac palpitation is noted with a rapid, pounding pulse and an increase in blood pressure. Nicotine poisoning involves central and peripheral nervous system effects consisting of initial stimulation followed by depression. Very rapid light headedness, severe nausea, vomiting, skeletal muscle weakness, prostration, tremor and convulsions can occur. Death is due to peripheral skeletal neuromuscular blockade. Hence, artificial ventilation is the most important therapeutic measure in treating a person with a potentially lethal nicotine overdose. Self-intoxication with Nicotiana tabacum and rustica historically was used by shamans and others for inducing stupor or narcosis [22]. Nicotiana tabacum was native to Pre-Conquest...