Synthesis And Activities Of Substituted Cinnamoyl Amino Acid Ester Derivatives

Food preservatives are commonly used in food processing to inhibit the growth of microorganism, prevent food spoilage and prolong shelf life of the product. Food preservatives has become an interesting research field and many scientists have payed much attention to search for the highly efficient and safe preservatives. In addition, multi-functional food additives have become an important orientation in developing the food additives. Thirty amino acid ester intermediates and forty-two hydroxycinnamoyl amino acid esters have been synthesized in our working. The target compounds were characterized by IR, MS and 1H NMR spectroscopy. The antimicrobial activity, antioxidative activity and inhibiting tyrosinase effect of these compounds were researched in vitro.1. The Preparation of hydroxycinnamoyl amino acid estersThe hydroxycinnamoyl amino acid esters were synthesized by retaining the biological activity part of cinnamate,i e the a, P-unsaturated carbonyl structure.30 amino acid ester hydrochlorides were prepared using dichloro sulfoxide or p-toluenesulfonic acid (TsOH) as catalyst, then through the carbonyl chloride method or EDC-HCl and HOBt procedure,42 hydroxycinnamoyl amino acid esters were synthesized.2. Anti-microbial characteristics of hydroxycinnamoyl amino acid estersThis paper studied the anti-microbial activity of hydroxycinnamoyl amino acid esters. Most of the compounds exhibit better anti-microbial activity comparing with cinnamic acid, but less active than benzoic acid, except for compounds a5 and compounds b6. The growth inhibition conditions of compounds a5 and compounds b6 on Eschericheae coli, Bacillus subtilis, Saccharomyces cerivisiae and milk spoilage microorganism were studied in different pH. It showed that compound a5 and compound b6 could effectively prolong adaptive phase and decrease growth quantity of Eschericheae coli, Bacillus subtilis, Saccharomyces cerivisiae, and milk spoilage microorganism. Compound a5 showed better inhibitory activities on milk spoilage microorganisms growth than benzoic acid at pH of 7 and 7.5.3. Free radical scavenging and antioxidative activity of hydroxycinnamic acid amide and ester analoguesIn order to find potential antioxidants with hydroxycinnamic acid moity we synthesized a series of hydroxycinnamic acid analogues and compared their capacity to scavenge 2,2-diphenyl-l-picrylhydrazyl (DPPH) radical and to protect human red blood cells (RBCs) from oxidative haemolysis. It was found that the caffeic amides exhibited the highest DPPH-scavenging activities while the higher hydrophobic ferulic amides demonstrated the highest antihaemolysis activities among the three different hydroxycinnamic analogues (Caffeic acid, ferulic acid, p-coumaric acid), and that hydroxycinnamoyl amides were more effective than their corresponding acid and ester compounds in both DPPH and RBC haemolysis test. This experiment proved that the radical scavenging activities of the compounds increased with the increasing numbers of hydroxyl groups or catechol moieties in DPPH-scavenging test, while in the emulsion system, the antioxidative activity of the test compounds depends not only on the hydroxyl groups but also on the partition coefficient (log P) or hydrophobicity of the compounds.4. The evaluation as tyrosinase inhibitorsHydroxylated cinnamic acid derivatives, such as, caffeic and ferulic acids are common in plant cells and have been reported to inhibit tyrosinase. Hydroxycinnamoyl amino acid esters were evaluated as tyrosinase inhibitors. The results demonstrated that most of target compounds had better inhibitory activities on tyrosinase than their parent compounds.