Sheng, Zhaojun, Dong, Chang-Zhi, Du, Zhiyun, Shi, Yiming, Pallois, Frédérique, Lu, Yang, and Zhang, Kun
(5 S,8 S,10a R)- tert-butyl 5-( tert-butoxycarbonylamino)-2,6-dioxooctahydro-1 H-pyrrolo[2,1-d][1,5]oxazocine-8-carboxylate 5, containing an original proline-like moiety, was prepared through Yamaguchi lactonization. However, it was observed that this 8 + 5 bicyclic lactone was spontaneously rearranged to the corresponding 7 + 5 bicyclic lactam under acid conditions, used to remove the Boc/ tBu protecting groups. Both core structures were confirmed by one-dimensional and two-dimensional NMR, as well as HRMS. The new proline-like moieties are unknown up to now, and the 7 + 5 bicyclic lactam, much more stable than its precursor, may represent a valuable template to develop constrained non-peptide mimetics. [ABSTRACT FROM AUTHOR]