Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 8, 2004
Publication Date: October 1, 2004
Citation: Compton, D.L., Laszlo, J.A., Isbell, T.A. 2004. Cinnamoyl esters of lesquerella and castor oil: Novel sunscreen active ingredients. Journal of the American Oil Chemists' Society. 81:945-951. Interpretive Summary: One of the missions at the National Center for Agricultural Utilization Research (a research lab within the USDA) is to develop new crops and new uses for crop products. Lesquerella is a plant that is native to the desert southwest with some species growing as far north as Tennessee. One of the most promising species, L. fendleri, has been grown in Arizona with yields of 1500 to 2000 lbs/acre. Research in our New Crops and Processing Technology group has been to improve the processing of the meal and develop new products from the lesquerella oil (an excellent alternative to castor oil, which is currently imported into the U.S.) and meal. Over the last year, a method has been developed to transform lesquerella oil into substances that may potentially be used in sunscreens. We are able to combine leaquerella oil and cinnamates (molecules similar to cinnamon) using only high temperatures. Several cinnamates absorb UV-B, the light from the sun responsible for sunburns. The result of the process is a cinnamate-oil that may have the desired properties needed for use in waterproof sunscreens. If developed as a sunscreen ingredient, the cinnamoyl-lesquerella oil would be made from all natural products, while providing a value added use for lesquerella oil. New, value added uses will make lesquerella a more attractive alternative cash crop for farmers.
Technical Abstract: Lesquerella and castor oil were esterified with cinnamic acid (CA) and 4-methoxycimmic acid (MCA). Esterification of the hydroxy oils reached 85% conversion with CA and 50% conversion with MCA. The hydroxyl oils were esterified at 200°C under a nitrogen atmosphere within a sealed system. Unreacted CA and MCA were removed from the reaction mixtures by sublimation at 100°C under vacuum. The resultant methoxycinnamic-oils possessed a broader, more blue-shifted ultraviolet (UV) absorbance, 250 to 350 nm with a max of 305 nm, compared to the cinnamic-oils which adsorbed from 260 to 320 nm, max of 273 nm. The methoxycinnamic-oils provide better UVB adsorption and, thus, are better candidates for sunscreen active ingredients. Esterifications of the hydroxy oils with MCA at 200 °C resulted in 40% of the MCA converted to undesirable byproducts. Esterifications with MCA performed at 175°C in the presence of a tin catalyst resulted in similar percent conversions to product without the degradation of MCA. Esterifications of lesquerella oil with MCA resulted in higher conversions, 43%, than analogous esterifications with castor oil, 29%. The hydroxyl groups of the lesquerella and castor provide the oils' excellent emolliency, lubricity, and non-comedogenicity in skin and personal care products. Therefore, reactions that only convert 50% of the available hydroxyl groups of the lesquerella oil to cinnamoyl-esters are preferred.