Mechanistic information and structure-based design methods have been used to design a series of nonpeptide cyclic ureas that are potent inhibitors of human immunodeficiency virus (HIV) protease and HIV replication. A fundamental feature of these inhibitors is the cyclic urea carbonyl oxygen that mimics the hydrogen-bonding features of a key structural water molecule. The success of the design in both displacing and mimicking the structural water molecule was confirmed by x-ray crystallographic studies. Highly selective, preorganized inhibitors with relatively low molecular weight and high oral bioavailability were synthesized.

Analysis of peptides by reverse-phase highpressure liquid chromatography would be simplified if retention times could be predicted by summing the contribution to retention of each of the peptide's amino acid side chains. This paper describes the derivation of values ("retention coefficients") that represent the contribution to retention of each of the common amino acids and end groups. Peptide retention times were determined on a Bio-Rad "ODS" column at room temperature with a linear gradient from 0.1 M NaCIO4, pH 7.4 or 2.1, at 0 min to 60% acetonitrile/0.1 M NaCIO4 at 80 min. The NaClO4, a chaotropic agent, was added to improve peak shape and to minimize conformational effects. Retention coefficients for the amino acids were computed by using a Hewlett-Packard 9815A calculator programmed to change the retention coefficients for all amino acids sequentially to obtain a maximum correlation between actual and predicted retention times. Correlations of 0.999 at pH 7.4 and 0.997 at pH 2.1 were obtained for 25 peptides including glucagon, oxytocin, [Metlenkephalin, neurotensin, and somatostatin. This high degree of correlation suggests that, for peptides containing up to 20 residues, retention is primarily due to partition processes that involve all the residues. Although steric or conformational factors do have some effect on retention, the data suggest that under the above chromatographic conditions the retention of peptides containing up to 20 residues can be predicted solely on the basis of their amino acid composition. This possibility was tested by using data taken from the literature.The possibilities for separating and isolating small peptides have been markedly improved by the introduction of reverse-phase high-pressure liquid chromatography (HPLC) (1-5). This technique depends upon the hydrophobic interactions between a hydrocarbonaceous column and the peptides to be separated: the more hydrophobic (lipophilic) the compound, the stronger its retention by the column. To elute strongly retained compounds, aqueous solutions (the "mobile phase") containing a large amount of organic solvent must be pumped through the column. Choice of the optimum mobile phase and chromatographic conditions for given peptides can be found by trial and error after qualitatively examining the balance of hydrophobic and hydrophilic amino acids present in the peptide. However, as noted by Molna'r and Horvath (1), it should be possible to obtain quantitative estimates of the hydrophobicity of the amino acids contained in a peptide, which will reflect their retention on the reverse-phase column. Estimates of hydrophobicity based on octanol/water partition coefficients exist for many but not all amino acids. By using such values, O'Hare and Nice (2) noted that the retention order for small peptides was generally correlated with the sum of the values for the most hydrophobic residues of the peptides. The many deviations they found between the observed order of elution and the lipophilicity estimates presumably derive from th...

A simple, rapid method is presented for the determination of acetylcholine (ACh) and choline (Ch) in neuronal tissue using HPLC with electrochemical detection. The method is based on the separation of ACh and Ch by reverse-phase HPLC and mixing the effluent as it emerges from the column with acetylcholinesterase and Ch oxidase, which converts endogenous Ch and Ch produced by the hydrolysis of ACh to betaine and hydrogen peroxide. Production of hydrogen peroxide is continuously monitored electrochemically. The sensitivity of the procedure is 1 pmol for Ch and 2 pmol for ACh. Specificity of the method is based on HPLC, two specific enzymatic reactions, and the detection of hydrogen peroxide.