How to Synthesize Wax Esters? Three Synthetic Routes

Wax esters are esters formed by long-chain fatty acids and fatty alcohols. Owing to their biodegradability and good lubricity, wax esters can be used as base materials for advanced lubricants and advanced emollient oils for aviation, machinery, and chemical industries as well as for daily cosmetics and other fields. Wax esters can be divided into saturated and unsaturated types. The wax esters produced in the marine environment are called marine wax esters and are mainly distributed in marine animals. The number of carbon atoms of fatty acids in marine wax esters is generally C14-C22, and in surface organisms, C20:5 and C22:6 are polyunsaturated fats. Oil fish is a deep-sea fish that contains many wax esters. More than 40% of its total weight is wax ester. Due to the high melting point of wax esters, the human body cannot decompose and absorb them. Therefore, after the human body ingests excessive wax esters, the intestines will be stimulated and diarrhea will occur due to inability to digest and absorb wax ester, but this will not cause poisoning. Synthetic route of wax esters in microorganisms Wax esters are important storage lipids in microorganisms. When cells contain too much free fatty acids, they are converted into non-toxic storage complexes such as wax esters to protect cells from damage. In 2002, Ishige et al. found that long-chain fatty alcohols for wax ester formation can be synthesized by the corresponding fatty acyl-CoA reduction reaction in two steps. Kalscheuer et al. took Acineto-bacter calcoaceticus strain ADP1 (later named as Acinetobacter bay-lyi strain ADP1) as the research object and conducted a detailed study on the biosynthetic route of the wax esters. First, an NADPH-dependent long-chain fatty acyl-CoA reductase (Acr1) catalyzes the reduction of fatty acyl-CoA to fatty aldehydes. Acr1 is located on the plasma membrane and catalyzes the reduction of C14-C22 acyl-CoA. It is further reduced to the corresponding fatty alcohol by an NADPH-dependent fatty aldehyde reductase. Wahlen et al. cloned the fatty aldehyde reductase in the bacterial wax ester synthesis route from Marinobacteraquaeolei VT8 for the first time. Finally, the wax ester synthase/ Acyl-CoA-diacylglycerol acyltransferase (WS/DGAT) catalyzes the esterification of fatty alcohols with long-chain fatty acyl-CoA to form wax esters. The Synthetic Route of Wax Esters in Plants The research on the synthesis of wax esters in plants was first carried out in Arabidopsis thaliana, and the wax esters were mainly synthesized through the acyl reduction route. In plants, fatty alcohols are formed differently. Kolattukudy’s research shows that in cabbage (Brassica olera-cea), the synthesis of primary alcohols requires a two-step reaction process and two separate enzyme catalysis, one is NADH-dependent fatty acyl-CoA reductase, which acts to convert the ultra-long chain fatty acids to fatty aldehydes; the other is an NADPH-dependent fatty aldehyde reductase that further reduces fatty aldehydes to primary alcohols. Vioque and Kolattuku-dy also demonstrated that in pea (Pisum sativum), the formation of fatty alcohols from very long-chain fatty acid precursors is accomplished by only one fatty acyl-CoA reductase. Also, although fatty aldehyde intermediates are required for fatty alcohol formation, these fatty aldehydes are not released. The synthesis route of wax esters in mammals Similar to plants, fatty acyl-CoA reductase first reduces fatty acyl-CoA into fatty alcohols and coenzymes using reducing NADPH, and then wax ester synthase catalyzes the transesterification of fatty acids and fatty alcohols to form wax esters. As wax esters are widely used in cosmetics, pharmaceutical and industrial applications, the demand for such types of lipids is on the rise.