Preparation and evaluation of radioiodinated (iodophenyl)cholines and their morpholinium and piperidinium analogues as myocardial perfusion imaging agents

General approach for the stereocontrolled construction of the beta-lactam ring in amino acid-derived 4-alkyl-4-carboxy-2-azetidinones

The first general approach toward the asymmetric synthesis of 4-alkyl-4-carboxy-2-azetidinones derived from amino acids is described. The stereoselective construction of the beta-lactam ring was achieved through base-mediated intramolecular cyclization of the corresponding N(alpha)-chloroacetyl derivatives bearing (+)- or (-)-10-(N,N-dicyclohexylsulfamoyl)isoborneol as chiral auxiliary (ee up to 82%).

Entry to New Conformationally Constrained Amino Acids. First Synthesis of 3-Unsubstituted 4-Alkyl-4-carboxy-2-azetidinone Derivatives via an Intramolecular Nα-Cα-Cyclization Strategy

A systematic study on the base-assisted intramolecular alkylation of N-benzyl-N-chloroacetyl amino acid derivatives is described. This study resulted in the first concise and versatile route to the preparation of 3-unsubstituted 4-alkyl-4-carboxy-2-azetidinones, to be included into the scarce family of beta-lactams with quaternary centers at the C(4) position. Particularly noteworthy is that the intramolecular N(alpha)-C(alpha)-cyclization of Phe and Leu derivatives afforded the corresponding beta-lactam derivatives with moderate enantioselectivity (up to 56%). It is suggested that, in these particular cases, the cyclization reaction proceeds by way of planar enolate intermediates, which possess dynamic chirality. The described sequence of reactions, that is compatible with commonly used protecting moieties for the alpha-carboxy group, cannot be applied to dipeptides, since the cyclization to the six-membered 2,5-diketopiperazine ring occurs preferentially.

Synthesis and evaluation of 1-[11C]methyl-4-aryl-piperazinium salts as myocardial imaging agents

Our previous study with radioiodinated 1-methyl-1-(2-hydroxyethyl)-4- phenylpiperazinium derivatives indicated that these compounds localize selectively in the rat myocardium. Based upon these results, 1-[11C]methyl-1-alkyl-4-phenylpiperazinium cations were synthesized and evaluated for their potential as myocardial imaging agents. Biodistribution studies were performed in rats and imaging studies in normal dogs. The results indicate high concentrations of 3-4% ID/g in the rat heart at 5 min, comparable to those obtained with the radioiodinated analogs. Sequential imaging of the canine heart showed a similar pattern of uptake. The level of activity reached at 20 min was maintained over the 1-h time period. These results suggest that the phenylpiperazinium agents may have potential application as myocardial imaging agents.