3-Methyl-2-butenyl caffeate

DFT study of the effect of solvent on the H-atom transfer involved in the scavenging of the free radicals (.)HO2 and (.)O2(-) by caffeic acid phenethyl ester and some of its derivatives.[Pubmed:25388279]

J Mol Model. 2014 Nov;20(11):2509.

H-atom transfer from caffeic acid phenethyl ester (CAPE), MBC (3-Methyl-2-butenyl caffeate), BC (benzoic caffeate), P3HC (phenethyl-3-hydroxycinnamate), and P4HC (phenethyl-4-hydroxycinnamate) to the selected free radicals (.)HO2 and (.)O2(-) was studied. Such a transfer can proceed in three different ways: concerted proton-coupled electron transfer (CPCET), electron transfer followed by proton transfer (ET-PT), and proton transfer followed by electron transfer (PT-ET). The latter pathway is sometimes competitive with SPLET (sequential proton loss electron transfer) in polar media. Analyzing the thermodynamic descriptors of the reactions of CAPE and its derivatives with co-reactive species-in particular, the free energies of reactions, the activation barrier to the CPCET mechanism, and their rate constants-appears to be the most realistic method of investigating the H-atom transfers of interest. These analyses were performed via DFT calculations, which agree well with the data acquired from experimental studies (IC50) and from CBS calculations. The CPCM solvation model was used throughout the work, while the SMD model-employed as a reference-was used only for CAPE. The main conclusion drawn from the analysis was that SPLET is the mechanism that governs the reaction of phenolic acids with (.)HO2, while PT-ET governs the reaction of phenols with (.)O2(-). In kinetic investigations of the CPCET process, the rate constant decreases as the solvent polarity increases, so the reaction velocity slows down.

Allergic contact dermatitis from propolis.[Pubmed:16536336]

Dermatitis. 2005 Dec;16(4):209-15.

Propolis is commonly used in cosmetic and medicinal preparations because of its antiseptic, antiinflammatory, and anesthetic properties. Its therapeutic qualities have been well documented. However, 1.2 to 6.6% of patients who are patch-tested for dermatitis are sensitive to propolis. The main allergens are 3-Methyl-2-butenyl caffeate and phenylethyl caffeate. Benzyl salicylate and benzyl cinnamate are less frequent sensitizers. Propolis is found in a number of "natural" products, including lip balms, cosmetics, lotions and ointments, shampoos, conditioners, and toothpastes. Dermatologists should consider patch testing with propolis in users of such remedies.

Evaluation of the main contact allergens in propolis (1995 to 2005).[Pubmed:16242084]

Dermatitis. 2005 Sep;16(3):127-9.

BACKGROUND: Propolis, the bee glue, is increasingly used in biocosmetics and for the self-treatment of various diseases. OBJECTIVE: Patients reacting to propolis were requested to participate in further testing with the breakdown constituents of the bee glue. METHODS: Twenty-seven patients agreed to be tested with 18 constituents, including four caffeates (the typical allergens of propolis) derived from the sticky exudates of poplar buds. RESULTS: Seven patients did not react to the propolis constituents tested. In the remaining 20 patients, the four caffeates produced strong reactions. Phenylethyl caffeate, which produced positive reactions in 20 patients, was the leading contact allergen. Benzyl caffeate elicited strong responses in 18 patients, and 3-Methyl-2-butenyl caffeate produced reactions in 17 patients. Geranyl caffeate produced positive reactions in 11 patients. The flavonoid tectochrysin gave positive results in 2 patients; ferulic acid, coumaric acid, and methyl cinnamate produced weak responses. CONCLUSIONS: In middle Europe, the caffeates are the responsible allergens in propolis allergy. Patients from other countries, where poplar trees do not grow, become allergic to other propolis constituents but not to the caffeates.

Propolis allergy (IV). Studies with further sensitizers from propolis and constituents common to propolis, poplar buds and balsam of Peru.[Pubmed:1600736]

Contact Dermatitis. 1992 Jan;26(1):34-44.

26 different compounds have been investigated experimentally for their sensitizing capacity in guinea pigs. 19 of these occur in propolis as well as in poplar bud exudates, and 14 of them are also found in balsam of Peru. 4 caffeates and benzyl isoferulate were found to be strong sensitizers. 7 compounds were moderate, and 13 compounds showed only weak sensitizing potency. Methyl cinnamate was negative. Patch tests in 11 propolis-sensitive patients once more revealed 3-Methyl-2-butenyl caffeate and phenylethyl caffeate as the major sensitizers. In addition to the 8 compounds already known to occur in propolis as well as in balsam of Peru, we detected 5 further substances that both materials have in common. Among these, benzyl isoferulate is considered a noteworthy sensitizer. Coniferyl benzoate, which was shown to be a moderate sensitizer, is present in fresh samples of balsam of Peru, while in propolis it has been detected only once so far. The flavonoid aglycones occurring in poplar bud exudates, and hence also in propolis, are weak sensitizers which play only a minor role in propolis hypersensitivity.

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