1,3-di(3-methoxybenzyl) thiourea and related lipid antioxidants

Natural lipids and oils are subject to oxidative degradation affecting color, odor, viscosity, and lubricity, which lowers the quality of the commercial products containing these lipids. In the food, cosmetics and pharmaceutical industries, maintaining high quality color and odor of oils and other lipids is important. Meadowfoam (Lininanthes alba) seed oil is more oxidatively stable than other vegetable oils and imparts this oxidative stability to other oils when mixed in combinations. This study was conducted to identify antioxidants in meadowfoam oil and to determine their properties. Structurally-related compounds were synthesized to compare to the antioxidant compound in meadowfoam. Compounds isolated from meadowfoam oil (L. alba), were concluded to be either a source of 1,3-di(3-methoxybenzyl) thiourea (3MBTU) or oxidation products from it. 3-Methoxybenzyl isothiocyanate (3MBITC) and 3-methoxybenzyl amine (3MBAm), which were identified in the oil as degradation products of the glucosinolate glucolimnanthin, reacted readily to form 3MBTU in meadowfoam oil, water and ethanol. 1,3-di(3-methoxybenzyl) urea, the oxygenated form of 3MBTU, was isolated from crude meadowfoam oil. 3MBTU and other disubstituted thioureas containing at least one 3-methoxybenzyl substituent were made from isothiocyanates and amines and the lipid solubility, antioxidant properties, toxicity (LC50), stability and spectral absorbance properties were determined. 3MBTU was an effective antioxidant in two different oxidative stability tests for mono- and polyunsaturated oils at the 0.1% level. It was also a stronger UVB absorber than most of the other disubstituted thioureas tested. Molecular models and calculations explained some of these results. The toxicity of 3MBTU was also very low compared with other thioureas and some commonly used lipid antioxidants. Solubility in meadowfoam oil was highest for 3MBTU, among those tested at 50 degreesC. In conclusion, 3MBTU, from meadowfoam oil, meadowfoam by-products, or synthesized appears to meet many of the criteria for an effective lipid antioxidant. (C) 2002 Published by Elsevier Science B.V.