Chapter 29 LIPIDS

Lipids (Greek lipos for fat) are organic compounds of natural origin that can dissolve in nonpolar organic solvents, such as chloroform, ether, benzene, but not in water. This group includes compounds different in chemical composition and structure, so there is no single comprehensive definition of lipids as of today. Lipids are important biological substances comprising living cells. The current chapter emphasizes the structure and chemical properties of lipids important for practical use in pharmacy.

29.1. Main structural components

With all structural diversity, the majority of lipids typically have two obligatory constituents in their composition: higher (long-chain) fatty acids and alcohols.

29.1.1. Higher fatty acids

Many higher carboxylic acids were first isolated from fats and therefore were called ?fatty?; accounting for the typical relatively long hydrocarbon chain, they are called higher fatty acids (HFA). Over 500 HFA representatives have been found in nature. However, just a little over 20 of them have a significant practical value.

According to their structure, most natural HFA are characterized by the following features: they are monocarboxylic, contain an even number of carbon atoms, have an unbranched hydrocarbon chain and the cis configuration of double bond(s) (if present).

The following types of higher fatty acids exist:

• saturated;

• unsaturated;

• modified.

Saturated higher fatty acids. Most commonly, lipids comprise acids with an unbranched chain, including 16, 18, 20, or 22 carbons (Table 29.1). The most widespread acids are palmitic and stearic acids typical of solid fats and several solid vegetable oils (e.g., cocoa oil, palm oil). The so-called medium-chain fatty acids, lau-ric (C₁₂) and myristic (C₁₄) acid, are typical of lipids of plants from the palm family.