The distribution of a homologous series of polyphenol derivatives of increasing lipophilicity has been determined in fish oil-in-water emulsions and nanoemulsions by the pseudophase model. One of the hypotheses on which the pseudophase model is based, is that its application is independent of the size of emulsion droplets. In agreement with our hypothesis, results showed that the smaller droplet size found in nanoemulsions does not affect partition constants of gallic acid (GA) and its esters. The antioxidant efficiency of GA and gallates in the emulsified systems used, correlated positively with the concentration of antioxidant at the interfacial region. The increase in the oil/water ratio increased the overall oxidative stability of emulsions but decreased the antioxidant efficiency of the more lipophilic derivatives. This can be assigned to the fact that, increasing the oil phase volume, the interfacial concentration decreased for the more lipophilic antioxidants.

BACKGROUND Controlling the interfacial concentrations of antioxidants (AOs) in oil‐in‐water emulsions can be regarded as a unique approach for increasing the efficiency of AOs in inhibiting the oxidation of lipids. Classical methods to determine the AO distribution in binary systems cannot be employed and their distribution needs to be assessed in the intact emulsion. RESULTS We have employed a well‐established kinetic method to determine the distribution of a homologous series of AOs derived of chlorogenic acid in olive oil‐in‐water emulsions and analyse the effects of AO hydrophobicity on their distributions and their efficiencies. Results indicate that variations in the efficiency of chlorogenates in emulsions are due to differences in their interfacial concentrations. Their interfacial concentrations AOI were much higher (20‐ to 150‐fold) than their stoichiometric concentrations. On the other hand, their concentrations in the oil region were 1.5‐ to 0.1‐fold. Results also show the complex effect of the oil‐to‐water ratio employed in the preparation of the emulsions on the (AOI) values. CONCLUSION Results highlight the key role of the interfacial region and of its composition (interfacial AO molarity, emulsifier concentration, oil‐to‐water ratio) in interpreting the efficiency of AOs in inhibiting lipid oxidation in emulsions. Thus, a careful modulation of these parameters is necessary to ensure optimum AO efficiency. © 2019 Society of Chemical Industry

Heterocyclic β-substituted alanine derivatives such as β-(pyrazol-1-yl) and β-(1,2,4-triazol-1yl)-alanine are synthesized in high yields by a Michael addition of heterocyclic nucleophiles to N,N-bis(tert-butyloxycarbonyl)dehydroalanine methyl ester, using mild reaction conditions and simple work-up procedures.

We have developed a modification of our previously reported high-yielding method for the synthesis of N,N-diacyldehydroamino acid derivatives to prepare N-monoprotected dehydroamino acids and dehydrodipeptides. Thus, several dehydroalanine, dehydroaminobutyric acid and dehydrophenylalanine derivatives have been prepared by treating the corresponding L-serine, L-threonine and D,L-3-phenylserine (threo-type) derivatives with 1 equiv. of di-tert-butyl dicarbonate and 4-(dimethylamino)pyridine. The reaction proceeded with the initial formation of an O-tert-butyl carbonate which, by treament with N,N,NЈ,NЈ-tetramethylguanidine, underwent β elimination to give the corresponding dehydroamino acid derivative. This two-step method can be carried out as a one-pot procedure and is stereoselective, giving only the Z isomer. The N-monoprotected dehydroamino acids were treated with N-bromosuccinimide and thereafter

With the aim to develop a practically useful, reductively more labile alternative to tosyl for protection of amino functions, initially a number of N-arenesulfonyl-protected heterocycles (pyrroles, imidazoles, indole, and carbazole) have been prepared and studied by cyclic voltammetry (CV). The recorded activation potentials vary from -1.32 to -1.99 V (vs SCE). In N-sulfonylazolides such as tosylindole the cathodic potentials are shifted by over 0.5 V compared to simple sulfonamides. An additional effect of the sulfonic acid component is also indicated. Among the compounds studied, 1-and 2-naphthalenesulfonylindole give CV peaks at about 0.4 and 0.2 V, respectively, less negative potential than tosylindole. To further investigate naphthalenesulfonyl for this purpose, we have also prepared a variety of simple 1-and 2-naphthalenesulfonyl derivatives and studied them similarly. They have activation potentials above -2.14 V and are all smoothly cleaved by Mg/ MeOH. The latter reagent is capable of cleaving N-arenesulfonyl derivatives that give CV peaks above -2.30 V, whereas Al(Hg) requires potentials above about -1.7 V. Selective cleavage of 2-naphthalenesulfonyl in the presence of tosyl by Mg/MeOH is demonstrated. Several examples of reductive cleavage of arenesulfonyl derivatives with Mg/MeOH, Al(Hg), and electrolysis on a preparative scale are given.