Natural Products Sources - Natural Products Chemistry: Sources, Separations, and Structures - page 1

1 Natural Products Sources
Sand is a natural product. But we will not cover the chemistry of silica. Natural prod-
ucts of interest are those organic compounds that contain at a minimum the element
carbon. Carbon (chemical symbol: C) has a valency of 4 and is bound to another
carbon either as a single, double, or triple bond. Carbon is also attached to other ele-
ments, typically other carbons, hydrogen (H), oxygen (O), and nitrogen (N); and also
sulfur (S) and phosphorous (P). The various combinations lead to the bewildering
array of natural products structures: some simple and others complex. Examples are
provided throughout the topic.
1.1 PRIMARY AND SECONDARY METABOLITES
Metabolites are intermediates in metabolic processes in nature and are usually small
molecules. A primary metabolite is directly involved in normal growth, development,
and reproduction, for example, fermentation products (ethanol, acetic acid, citric and
lactic acid) and cell constituents (lipids, vitamins, and polysaccharides). A secondary
metabolite is not directly involved in those processes and usually has a function but
is not that important for the organism (e.g., antibiotics, pigments, and carotenoids).
Metabolic processes and enzymatic reactions begin from simple building blocks,
which are outlined in Figure 1.1. The building blocks and pathways are further
elaborated upon in Chapter 4. These metabolites are divided into various classes
depending on the functionality of the molecule (e.g., phenolic, alkaloid, steroid),
and are discussed in detail in Chapters 6 and 7. Several simple but important natural
products structures and their sources in nature are described next.
EXAMPLE 1.1: PHENOLIC COMPOUNDS FROM THE WILLOW BARK
The active ingredient in willow bark is salicin, converted in the body into salicylic
acid (Figure 1.2). The presence of a phenol is recognized by the attachment of
an OH group to the benzene ring. Substitutions on the phenolic group of various
natural products include, but are not limited to, methyl, acetyl, and ether linkages.
HISTORICAL NOTE
Chewing the willow bark from the tree Salix alba reduced fever and inflam-
mation, and was recognized by ancient Greek physician Hippocrates to possess
health benefits. In the 1800s, pharmacists created salicylic acid in its acetylated
form (acetylsalicylic acid), more commonly known as aspirin. Aspirin was first
isolated and synthesized by Felix Hoffmann, a chemist with the German com-
pany Bayer and marketed in 1897. Thus, the most widely used drug in the world
continues to be aspirin.
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