Z-glycine N-hydroxysuccinimide ester

Aim: The aim of the study was to establish a novel type of covalently mucus-binding polymers by targeting selectively amino groups within mucus glycoproteins. Methods: N-Hydroxysuccinimide (NHS) was attached to carboxylic groups of polyacrylic acid (PAA). The reaction was mediated by the coupling reagent N,N'-dicyclohexylcarbodiimide (DCC) achieving polymeric NHS esters being able to form amide bonds with free amino groups. The chemical structure of the obtained conjugates was characterized via FTIR- and UV spectroscopy. Reactivity towards mucosal amino groups was evaluated UV spectrometrically upon addition of L-glycine. Furthermore, tensile force evaluations on intestinal mucosa as well as rheological experiments with mucus were performed in order to prove mucoadhesive potential. Results: Depending on the amount of NHS added to the synthesis, coupling rates of 876 to 1820 µmol NHS per gram polymer were obtained. Kinetic studies of amide bond formation showed a substrate dependent reaction velocity. Rheological synergism of PAA-NHS was proven by a 7.9-fold increased mucus viscosity compared to the control polymer. In further mucoadhesion studies PAA-NHS showed a 5.5-fold improved adhesion time compared to unmodified PAA. Tensile force evaluation confirmed these results with a 1.7-fold higher maximum detachment force (MDF) and 2.7-fold increased total work adhesion (TWA) for PAA-NHS compared to the unmodified control polymer. Conclusion: The results of the present study provide strong evidence that coupling NHS to polymers could be a promising tool for the development of novel mucoadhesive excipients.

We have developed a protocol for the direct coupling between methyl ester protected amino acids and the chlorido-gold(I)-phosphane (p-HOOC(C6H4)PPh2)AuCl. By applying the EDC·HCl/NHS strategy (EDC·HCl = N-ethyl-N'-(3-(dimethylamino)propyl)carbodiimide hydrochloride, NHS = N-hydroxysuccinimide), the methyl esters of l-phenylalanine, glycine, l-leucine, l-alanine, and l-methionine are coupled with the carboxylic acid of the gold complex in moderate to good yields (62-88%). All amino acid tagged gold complexes were characterized by (1)H and (13)C NMR spectroscopy and high-resolution mass spectrometry. As corroborated by measurement of the angle of optical rotation, no racemization occurred during the reaction. The molecular structure of the leucine derivative was determined by single-crystal X-ray diffraction. In the course of developing an efficient coupling protocol, the acyl chlorides (p-Cl(O)C(C6H4)PPh2)AuX (X = Cl, Br) were also prepared and characterized.

A new synthetic approach has been applied to obtain novel di-, tetra-, and (multi)-peptide containing polymer conjugates in quantitative yields with a high degree of conjugation. Bis-(N-hydroxysuccinimidyl) esters of PEG (Mw = 200, 600, 1400, 2000, and 3400) were synthesized and studied in a condensation reaction with synthetic peptides: glycine-glycine-tyrosine-arginine (GGYR), a model peptide, and glycine-arginine-glycine-aspartic acid-tyrosine (GRGDY), a sequence known to promote cell adhesion and aggregation. Tetra-substituted derivatives of PEG-based conjugates were synthesized by coupling L-aspartic acid and L-aspartyl-L-phenylalanine through a condensation procedure in organic media. Poly(acrylic acid) and co-polymers (Mw = 2000 and 5000) were studied as a model of multifunctional linear polymers in the reaction with L-tryptophan and GGYR. Alternative polymer-(multi)-peptide conjugates were successfully synthesized using Starburst dendrimer PAMAM (G = 3), 'short' and 'long'-chain PEG-based active esters and GRGDY. The structure of the intermediate precursors and peptide-conjugates was confirmed by spectral (UV-Vis, FTIR, H-NMR) and chromatographic (RP-HPLC and SEC) methods. By varying the properties of the interconnecting polymer--such as hydrophobicity, molecular weight, and functionality--a set of polymer-GRGDY conjugates was synthesized.