ÿþDrugs of Natural Origin

Author: Gunnar Samuelson

Year of Publication: 1999, Gunnar Samuelsson and Apotekarsocieteten

Swedish Parmaceutical Press, ISBN: 91862274813

The book of Drugs of Natural Origin is designed as a textbook for students of Pharmacognosy and hence it uses an easy and comprehensive language. The author well-defined new terminology and re-iterate commonly used words in pharmacognosy.

The author introduces the book by emphasizing that a proportion of current commercially available drugs originates for the nature. Drugs may come from plant's primary parts or secondary metabolites, animals and microorganism. In chapter one the author also stated the current perspective of pharmaceutical industries in developing and isolating compounds with both new structures and new biological activities.

Further in chapter two, crude drugs which is the starting material from which chemically pure compounds can be isolated are discussed in great detail. Crude drugs include whole plants or parts of plants, extracts and exudates and parts of animals. The chapter reveals the factors affecting cultivation of medicinal plants. These can be external such as climate, soil, irrigation, and infestation or internal such as methods of propagation, plant breeding and mutation. Harvesting and post harvesting treatments are briefly mentioned and overviews of methods of isolation of pure compounds and their subsequent quality controls are given sufficiently.

Plant tissue culture as a modern biotechnology tool for obtaining secondary metabolites or reducing mutation of differentiated plants is given a full chapter to indicate the importance of this aspect in pharmacology.

Photosynthesis in plants is taken as a general example of biosynthetic pathways for formation of pharmacologically active compounds. Chemical structures of all compounds involved in photosynthesis are elucidated and described clearly in chapter 4. From this chapter onwards pharmacologically active natural products are grouped according to biosynthetic principles.

Being the product of photosynthesis, carbohydrates are subsequently discussed early in chapter 5 and their biosynthetic derivatives are explained in terms of methods of isolation, preparation, chemical structures, pharmaceutical usage and their interaction.

Two the commonest biosynthetic pathways related to carbohydrates and derivatives are shikimate and acetate are described in chapter 6 and 7, respectively. These both pathways are biosynthetic series in which aromatic compounds are formed in nature. The precursor in the shikimate pathways is shikimic acid that can be used in the biosynthesis of gallic acid and tannin, phenylalanine, tyrosine, tryptophan, and groups of phenylpropanes. Shikimic acid itself can be synthesized from aldol condensation of phosphoenol pyruvate and the carbohydrate 4-phospho-D-erythrose.

While the precursor in acetate pathways is pyruvic acid that is formed from carbohydrate. Two main routes originate with acetate: the acylpolymalonate pathway leading to fatty acids and polyketides and the isopentenyl diphosphate pathway that gives terpenes and steroids. Although the book presents compounds based on their biosynthetic pathways, it also contains broad cover-ups about certain topics. For example, anthraquinone biosynthesis is first discussed under the heading of acylpolymanonate pathway and then supplemented by the shikimic acid pathways because in certain plant as such Rubia tinctorum both pathways are responsible in producing anthraquinones.

In most of biosynthetic reactions, enzymes, catalisators and reaction conditions are provided and their sources are often given. Moreover, several attractive and colorful pictures are selected to show where those particular biosynthetic products can be found. Similarities and differences of a particular product from other pharmacologically active compounds are remarked with full interest.

Chapter 8 of the books sets the overview of formation of amino acids and incorporates the previous information in chapter 6 and 7 about biosynthetic pathways of aromatic compounds. Amino acids are grouped accordingly to (-ketoglutaric acid group (glutamine, proline, hydroxyproline, aspartic acid, ornithine and arginine), pyruvic acid group (alanine, valine and leucine), oxalacetic group (asparagine, lysine, threonine, methionine and isoleucine), Serine group (serine, glycine, cysteine, cystine and histidine) and aromatic amino acids (tyrosine, phenylalanine and tryptophan). Further these amino acid in health issue are separated into either essential or non-essential amino acids. The essential amino acids mean that they have to be supplied from diets for their availability.

Subsequently chapter 9 discusses the natural products derived bio-synthetically from amino acids. Before further into detail the chapter has a brief explanation regarding contemporary notation of amino acids whether the three-letter-code or the one-letter-code. This coding system will help reader understand further amino acid derivatives. However, the book is only concentrating on some enzymes isolated from plants, some toxicologically interesting proteins and peptides of plant origin, lectins and snake venom as amino acid derivatives.

Amino acids also form alkaloids with the integration of other precursors such as terpenes and steroids into the final alkaloid skeleton. However, the author discussed alkaloids separately in chapter 10 that classifies the alkaloids based on the biosynthesis of main ring system. Under this category, there are 15 major differences of alkaloid backbone.

Based on structures and origin, it is hard to define alkaloids and hence the author boldly defines alkaloids as follows: a cyclic organic compound containing nitrogen in a negative oxidation state that is of limited distribution among living organisms.

Alkaloids are not found in all plant families. The apocynaceae are by far the richest source of alkaloids and followed by papaveraceae and fabaceae. Due to unclear function of alkaloids in a plant it is recognized as a secondary metabolite, which is hypothetically used mainly for defense against external attack.

Chapter 11 compiles three purine derivatives including caffeine, theobromine and thephylline in one group as they are practically devoid of basic properties despite of sometimes being categorized as alkaloids for having nitrogen on the ring and pharmacological activity.

Further chapter 12 describes 12 steps of biosynthetic formation of vitamin B12 whose chemical elucidation is characterized in Escherichia coli. B12 is one of the constituents of vitamin B complex that is abundantly found from dried yeast of brewing fermentation. Vitamin B12 has a complicated structure having a corrin ring.

Finally the last chapter concludes the book in two pages mentioning about allergy and allergens. They are included because some of pharmacological active compounds such as penicillin can promotes allergy for certain people although pollen is the most well-known allergen. Cunningly, sodium cromoglycate isolated from fruits of the Egyptian plant Ammi visnaga (L.) Lam. (Apiaceae) is usually used to alleviate common allergic effects.

In overall, the book is well presented and can provide quick searched information regarding new and contemporary issues in pharmacology. Nevertheless, being a textbook it contains lots of chemical structure that can slow down and impede the learning of self- learner and hence this book will be more beneficial if accompanied by several tutorials and lectures.

Each chapter is split into several little subheadings that enable readers to memorize better and encourage readers to fully comprehend each section before moving to another subheadings or chapter.

At the end of each chapter, related references are listed for further reading recommendation. This is very helpful especially in digging out more detail information about special issues. This promotes a better understanding because reading the original articles or papers after knowing a little bit information gives clearer insights.

This book follows a continuous layout and hence reading the information randomly can hardly satisfy a reader because the previous information should be understood better in order to understand the next section although the author sometimes refers a topic of interest to other related pages in the book.

The number of words and sentences per pages of the book is suitable for a fun and light reading and the paper size is ergonomic and can be easily handled.

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