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Carvacrol (CAR), a natural monoterpene particularly abundant in plants belonging to the Lamiaceae family, has recently attracted much attention for its many biological properties (antioxidant, anti-inflammatory, neuroprotective, antitumour, antibacterial, and several others). However, CAR has poor chemical-physical properties (low water solubility and high volatility), which hamper its potential pharmacological uses. In this paper, the synthesis and antimicrobial evaluation of 23 carvacrol derivatives (WSCP1-23) against a panel of selected gram-positive and gram-negative bacteria are reported. Using the prodrug approach, CAR hydrophilic (WSCP1-17) and lipophilic prodrugs (WSCP18-23) were prepared. Notably, CAR water solubility was increased by using polar neutral groups (such as natural amino acids) with the aim of improving oral drug delivery. On the other hand, CAR lipophilic prodrugs, obtained by prenylation of CAR hydroxyl group, were designed to promote membrane permeation and oral absorption. Our results revealed that WSCP1-3, showing the highest water solubility (>1700-fold compared to that of CAR), possessed good antibacterial activity against gram-negative bacteria with MIC values comparable to those of CAR and antifungal properties against different species of Candida. WSCP18-19 were the most promising prodrugs, showing good antibacterial profiles against gram-positive bacteria by interfering with the biofilm formation of Staphylococcus aureus and Staphylococcus epidermidis. Moreover, WSCP18-19 resulted more stable in simulated fluids and human plasma than WSCP1-3. Toxicity studies performed on human erythrocytes and HaCaT cells revealed that all WSCPs were not toxic at the tested concentrations., (Copyright © 2019 Elsevier Masson SAS. All rights reserved.)

Herein is described the synthesis of novel glycine-α-methyl-proline-containing tripeptides (GP(Me)X tripeptides namely GP(Me)R, GP(Me)K, and GP(Me)H) with the aim of obtaining derivatives highly stable in human plasma and able to counteract neuroinflammatory processes that are distinctive of neurodegenerative pathologies. The syntheses of GP(Me)R, GP(Me)K, and GP(Me)H were all achieved both by introducing the Pro(Me) residue into the Gly-Pro-Arg (GPR) sequence in place of the native Pro in P2 position and replacing the basic amino acid Arg in P3 position by Lys or His. Results showed that all novel GP(Me)X tripeptides are stable in human plasma (t1/2 > 51 h) and that GP(Me)H - generating stable intramolecular H-bond in a C11-turn by interaction of His imidazole ring and Gly carbonyl group - restored physiological levels of nitric oxide deriving from neuronal NOS (nNOS) activity, thus preventing the inflammatory response by suppression of the NF-kB activity and, consequently, the expression of inflammatory genes such as inducibile NOS (iNOS). Therefore, GP(Me)H could be a lead compound for further development of peptidomimetics able to contrast neuroinflammatory processes., (Copyright © 2015 Elsevier Masson SAS. All rights reserved.)