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6.6: Saccharolipids, polyketides, and prenols

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    Learning Objectives
    • Define and understand the basic structural features of saccharolipids, polyketides, and prenols.
    • Define mono-, sesqui-, di-, and tri-terpenes and recognize isoprene units in terpenes, terpenoids, and steroids.

    Saccharolipidsclipboard_ef53c21fc2b2b898c4ff80ebb99ea853f.png

    Saccharolipids are fatty acids linked to a saccharide (carbohydrate) backbone by linkages other than glycosidic linkages. They are compatible with membrane bilayers. For example, saccharolipid lipid A found in E. Coli is shown in the figure on the right.

    Polyketides

    Polyketides are a broad class of natural products derived from \(\beta\)-polyketones, i.e., compounds containing \(\ce{[-\!\!{\overset{\overset{\huge\enspace\!{O}}|\!\!|\enspace}{C}}\!\!-CH2{-}]_{n}}\) repeat units in their backbone or their reduced forms, such as \(\ce{[-\!\!\!\!\!{\overset{\overset{\huge\enspace\enspace{OH}}|}{C}}\!\!\!\!\!-CH2{-}]_{n}}\), and \(\ce{[-CH2-CH2{-}]_{n}}\). Polyketides are important in the pharmaceutical industry. They are used as antimicrobial, antiparasitic, and anticancer agents; some are toxins. About 20% of the top-selling medicines are polyketides. Some examples of medically important polyketide products are shown below.

    clipboard_e56c24260f8b3148a37d9c654478b8928.pngTetracycline -an antibiotic
    clipboard_e773fb1527eafa7a21f072e3d7bdc8f7e.pngErythromycin A -an antibiotic
    clipboard_e2b0bb193c8d3d0976b69c5b852f45565.pngGeldanamycin -an antitumor antibiotic
    clipboard_eb4f08c974c4e0499ed354ec61786457d.pngAflatoxin B1 -an aflatoxin

    Prenols

    Prenols are synthesized from five-carbon isoprene precursors: isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP), as shown in Figure \(\PageIndex{1}\) (left). The five-carbon skeleton of isoprene units in these products can often be easily distinguished, as shown in by different color sections of some examples in Figure \(\PageIndex{1}\) (right). Since they contain a multiple of five \(\ce{C's}\) in their skeleton, they are also classified as monoterpens (10 \(\ce{C's}\)), sesquiterpenes (15 \(\ce{C's}\)), diterpenes (20 \(\ce{C's}\)), triterpenes ((30 \(\ce{C's}\)), and tetraterpenes (40 \(\ce{C's}\)). Terpenoids are modified terpenes that contain additional functional groups, usually oxygen functional groups as those shown in \(\PageIndex{1}\) (right).

    clipboard_e838a3088735e9d1e0d852ec93fa9eecf.png
    clipboard_e694930d1a2f93df33552521d39f428fa.png
    Figure \(\PageIndex{1}\): Dimethylallyl pyrophosphate (DMAPP) and isopentenyl pyrophosphate (IPP) condense to produce geranyl pyrophosphate, a precursor to all terpenes and terpenoids (left, Copyright; Andrew Murkin, CC0, via Wikimedia Commons) and structure of Isoprene, limonene, farnesol, and retinol, respectively, showing isoprene skeleton in these products in different color sections (right, Copyright; Calvero., Public domain, via Wikimedia Commons)
    .

    Steroids -other lipids described later are derived from triterpene squalene, as illustrated in Figure \(\PageIndex{2}\).

    clipboard_e316a8aeefdb9eebe623616e0182db169.png
    Figure \(\PageIndex{2}\): A simplified scheme for steroid biosynthesis via terpenoid intermediates: isopentenyl pyrophosphate (IPP), dimethylallyl pyrophosphate (DMAPP), geranyl pyrophosphate (GPP) and squalene. (Copyright; Fvasconcellos, original by Tim Vickers, Public domain, via Wikimedia Commons)

    This page titled 6.6: Saccharolipids, polyketides, and prenols is shared under a Public Domain license and was authored, remixed, and/or curated by Muhammad Arif Malik.