Polyketide

As polyketides refers to a large group of natural substances, which is composed with respect to their chemical structures and pharmacological properties of highly heterogeneous. They share the biosynthesis via the so-called polyketide pathway. Many polyketides are of high importance as drugs, including antibiotics such as the tetracyclines or erythromycin, the anticancer drugs doxorubicin and epothilones and the antiparasitic agent avermectin.

Biosynthesis

Special enzyme complexes, the polyketide synthases form of simple, coenzyme A activated acyl groups (usually acetyl -CoA, malonyl -CoA) precursors of polyketides. Depending on the number of involved in the synthesis of acyl -CoAs can speak of Tetraketiden (four), Pentaketiden (five) etc.. This stepwise chain extension is similar to the fatty acid synthesis. In contrast to this, however, rarely a reduction in an aliphatic chain takes place. Each acetyl building block of the chain can remain at various stages of modifications that theoretically lead to fatty acid ( keto group > hydroxy > double bond > single bond ). Other enzymes reactions (eg cyclization, methylation or oxygenation ) complete the biosynthesis of polyketides.

Structural diversity

The diversity and complexity is evidenced by a few examples: One of the simplest polyketides is the 6- methyl salicylic acid. From complex natural vegetable dyes such as flavonoid quercetin, the mycotoxins zearalenone, Alternariol or aflatoxins, the macrolide antibiotic erythromycin or the polyene antifungal agent amphotericin B (also a macrolide ). Particularly complex structures occur in the polyketide of marine organisms, such as the maitotoxin or palytoxin.