Malic acid biological activities

There are some classes of compounds present in seawater which have known biological activity but have received little attention. Compounds involved in chemical communication, especially halogenated compounds, will be discussed in other chapters. Other compounds of interest are those involved in the citric acid cycle, the major pathway of metabolism in almost all cells. Citric acid cycle intermediates and reactions are involved in the biosynthesis of most of the major metabolites, from amino acids and carbohydrates to long-chain fatty acids and porphyrins (Mahler and Cordes, 1971). The intermediates, such as succinic, fumaric, malic, oxaloacetic, citric, gly-oxylic, and oxoglutaric acids are present in almost all organisms and are certainly being produced in the sea. 

The chemistry discussed in this section illustrates various techniques used to manipulate each of the four carbon sites of malic acid derivatives, leading ultimately to useful chiral intermediates, biologically active compounds, or interesting natural products. 

Functional groups like the -carboxyhc acid in malic add were also used to immobilize the carbonyl precursor by mask-linking it to suitable supporting resins. This allows for the generation of libraries of tetronic adds with potential biological activity. The potent enzyme inhibitor 3-palmitoyl-5-hydroxymethyl-tetronic acid RK-682 (36) was prepared in this way [34]. It had originally been isolated from various strains of Actinomycetes and Strep-tomycetes [35] and was found to inhibit HIV-1 protease and various other protein phosphatases such as VHR (vaccinia VH-1 related phosphatase) and... 

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