title: Design, synthesis and characterization of linear unnatural amino acids for skin moisturization.
abstract: OBJECTIVE
  This work aimed to design, synthesize and characterize replacement natural moisturizing factor (NMF) composed of modified hygroscopic linear amino acids to pre-empt or repair skin barrier dysfunction.
  
  
  METHODS
  Following synthesis and characterization, thermo-gravimetric analysis and quantum mechanics molecular modelling quantified and depicted water binding to the new compounds. Deliquescence relative humidity demonstrated the water-scavenging ability of the compounds, whereas snake skin moisturizing studies showed they increased water uptake into snake skin.
  
  
  RESULTS
  From thermal analysis, N-hydroxyglycine showed greatest water-holding capacity followed by N-hydroxyserine, l-homoserine and α-hydroxyglycine; coupled with quantum mechanics molecular modelling, between 8 and 12 molecules of water could associate with each molecule of either N-hydroxyglycine, N-hydroxyserine or l-homoserine. All of our modified amino acids were efficacious and induced similar or greater water uptake compared with the established moisturizing compounds hyaluronic acid, glycerine and urea in snake skin. Incorporated at 10% in Oilatum, N-hydroxyserine induced >200% greater moisture uptake into dry snake skin compared to treatment with water alone, with efficacy related to the molecule structure and ability to bind to 12 water molecules. Oilatum cream spiked with all our unnatural amino acid hydrotropes increased water uptake into snake skin compared with Oilatum alone. The compound series was designed to elucidate some structure - efficacy relationships. Amino acid chirality did not affect the water-holding capacity but did affect uptake into skin. Compounds with high melting points and bond energies tended to decrease water-holding capacity. With isosteric replacement, the more electronegative atoms gave greater water-holding capacities.
  
  
  CONCLUSIONS
  This work demonstrates the potential of unnatural amino acid hydrotropes as skin moisturizers and has developed some predictive 'rules' for further design and refinement of chemical structures.
authors.affiliation: Department of Pharmacy, University of Reading, PO Box 226, Whiteknights, Reading, RG6 6AP.|MedPharm Ltd., 50 Occam Road, Surrey Buisness Park, Guildford, GU2 7AB, UK.
authors.forename: N R
authors.initials: NR
authors.lastname: Arezki
authors.affiliation: Department of Pharmacy, University of Reading, PO Box 226, Whiteknights, Reading, RG6 6AP.
authors.forename: A C
authors.initials: AC
authors.lastname: Williams
authors.affiliation: Department of Pharmacy, University of Reading, PO Box 226, Whiteknights, Reading, RG6 6AP.
authors.forename: A J A
authors.initials: AJ
authors.lastname: Cobb
authors.affiliation: MedPharm Ltd., 50 Occam Road, Surrey Buisness Park, Guildford, GU2 7AB, UK.
authors.forename: M B
authors.initials: MB
authors.lastname: Brown
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D000818:Animals; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D033362:Powder Diffraction; D012879:Skin Physiological Phenomena; D012911:Snakes; D013055:Spectrophotometry, Infrared; D013818:Thermogravimetry; D014870:Water Loss, Insensible
chemical_list: D000596:Amino Acids
keywords: chemical synthesis; deliquescence relative humidity; delivery; hygroscopic; natural moisturizing factor; skin barrier