Both optical isomers of a quinazoline alkaloid, vasicinone, were synthesized by two different methods. The first method used (3S)-3-hydroxy-gamma-lactam as a chiral synthon, which was, after O-TBDMS protection, o-azidobenzoylated followed by treatment with tri-n-butylphosphine to afford (S)-(-)-vasicinone via the tandem Staudinger/intramolecualr aza-Wittig reaction. The second method utilized asymmetric oxygenation of deoxyvasicinone with (1S)-(+)- or (1R)-(-)-(10-camphorsulfonyl)oxaziridine (the Davis reagent), respectively. The aza-enolate anion of deoxyvasicinone was treated with (S)-(+)-reagent to afford (R)-(+)-vasicinone in 71% ee, while the reaction with (R)-(-)-reagent gave (S)-(-)-vasicinone in 62% ee. The optical purity was analyzed by HPLC on specially modified cellulose as a stationary phase. These results provided a facile method to prepare both optical isomers of vasicinone and confirmed the recently reversed stereochemistry of natural (-)-vasicinone.
alpha-[(3S)-3-[[(S)-1-(Ethoxycarbonyl)-3-phenylpropyl]amino]-2-oxo-6 or 7-phenylperhydroazepin-1-yl]acetic acids (monoester monoacids) and their dicarboxylic acids were synthesized, and their angiotensin-converting enzyme (ACE) inhibitory activities were evaluated. The dicarboxylic acids having phenyl substituents at the 6R, 6S, and 7S positions on the azepinone ring showed potent inhibition in vitro. The corresponding monoester monoacids, when administered orally, suppressed the pressor response to angiotensin I administered intravenously. The monoester monoacids having the phenyl substituent at the 6-position showed a longer duration of action than one having the substituent at the 7-position. The structure-activity relationship was studied on the basis of the conformational energy calculation.
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