Nα-Fmoc-L-histidine

Microwave energy represents an efficient manner to accelerate both the deprotection and coupling reactions in 9-fluorenylmethyloxycarbonyl (Fmoc) solid phase peptide synthesis (SPPS). Typical SPPS side reactions including racemization and aspartimide formation can occur with microwave energy but can easily be controlled by routine use of optimized methods. Cysteine, histidine, and aspartic acid were susceptible to racemization during microwave SPPS of a model 20mer peptide containing all 20 natural amino acids. Lowering the microwave coupling temperature from 80 degrees C to 50 degrees C limited racemization of histidine and cysteine. Additionally, coupling of both histidine and cysteine can be performed conventionally while the rest of the peptide is synthesized using microwave without any deleterious effect, as racemization during the coupling reaction was limited to the activated ester state of the amino acids up to 80 degrees C. Use of the hindered amine, collidine, in the coupling reaction also minimized formation of D-cysteine.

Cone snail venoms provide a largely untapped source of novel peptide drug leads. To enhance the discovery phase, a detailed comparative proteomic analysis was undertaken on milked venom from the mollusk-hunting cone snail, Conus textile, from three different geographic locations (Hawai'i, American Samoa and Australia's Great Barrier Reef). A novel milked venom conopeptide rich in post-translational modifications was discovered, characterized and named α-conotoxin TxIC. We assign this conopeptide to the 4/7 α-conotoxin family based on the peptide's sequence homology and cDNA pre-propeptide alignment. Pharmacologically, α-conotoxin TxIC demonstrates minimal activity on human acetylcholine receptor models (100 μM, <5% inhibition), compared to its high paralytic potency in invertebrates, PD50 = 34.2 nMol kg(-1). The non-post-translationally modified form, [Pro](2,8)[Glu](16)α-conotoxin TxIC, demonstrates differential selectivity for the α3β2 isoform of the nicotinic acetylcholine receptor with maximal inhibition of 96% and an observed IC50 of 5.

A literature overview is given of HPLC methods currently in use to determine amino acids as their 9-fluorenylmethyloxycarbonyl (FMOC) derivatives. On the basis of the detailed literature overview an exhaustive derivatization study was performed with 22 amino acids, applying photodiode array (DAD) and fluorescence (FL) detection simultaneously, in order to clear up the controversial points of FMOC derivatization. Model investigations have been carried out as a function of the reaction time and reaction conditions, such as the molar concentration of the reagent, the molar ratios of the reactants, the pH and the solvent composition of the reaction medium. Special emphasis was put (i) on the evaluation of the blank values of the reagents, as a function of the composition and that of the pH of the reaction medium, (ii) on the unambiguous quantitation of all amino acids, including the less reactive aspartic and glutamic acids, as well as on the formation and transformation of histidine and tyrosine, existing partly, as single (N-FMOC-histidine, N-FMOC-tyrosine), partly as double labeled species (N,NH-FMOC-histidine, N,O-FMOC-tyrosine).

We have studied the dynamic interaction of surfactants with carbon surfaces by using a series of Fmoc- (N-(fluorenyl-9-methoxycarbonyl)) terminated amino acid derivatives (Fmoc-X, where X is glycine, tyrosine, phenylalanine, tryptophan, or histidine) as a model system. In these systems, highly conjugated fluorenyl groups and aromatic amino acid side chains interact with the carbon surface, while carboxylate groups provide an overall negative charge. Ideal carbon surfaces were selected which possessed either predominantly macroscale (graphite) or nanoscale features (multiwalled carbon nanotube (MWNT) mats). The adsorption equilibrium for the Fmoc-X solutions with the graphitic surfaces was well-described by the Freundlich model. When a library containing various Fmoc-X compounds were exposed to a target graphite surface, Fmoc-tryptophan was found to bind preferentially at the expense of the other components present, leading to a substantial difference in the observed binding behavior compared to individual adsorption experiments.