Alkyl- and Acyl-Derivatives of Copsinine and Pseudocopsinine and Their Crystal Structures

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Acyl- and alkyl-derivatives at the N1 and N4 atoms, respectively, of the indoline alkaloids copsinine (1) and pseudocopsinine (2), which were isolated from the plant Vinca erecta, were synthesized. Alkaloids 1 and 2 reacted with alkyl halides to give N4 substitution; with acetic anhydride, N1. In turn, N1-acyl-1 and -2 reacted with alkyl halides to bond the alkyl radical to the N4 position. Reaction products were identified using IR spectroscopy and HPLC-MS. Their structures were elucidated by X-ray crystal structure analyses (XSAs). The tetrahedral hybridization of N1 in the indoline alkaloids was favorable for forming their N1-acetyl derivatives, which is improbable in indole and α-methyleneindoline alkaloids.