A new semisynthetic pyrrolizidine alkaloid, 9-O-[(±)-2-hydroxy-2-phenylbutyryl]retronecine N-oxide (2a), was synthesized and found to be more active than indicine N-oxide (1) on which it was modeled. 9-O-[(S)-(+)-2-hydroxy-2-phenylbutyryl]retronecine (5) and its diastereomer, 9-O-[(R)-(−)-2-hydroxy-2-phenylbutyryl]retronecine (6), were prepared, and their detailed 1H NMR spectra are presented. Conformational analyses of these molecules in solution are discussed on the basis of their NMR analyses and knowledge of their absolute configurations. © 1982, American Chemical Society. All rights reserved.