Pulsed Voltammetry of an Aspidosperma Alakaloid: Vindoline

There is steady interest in the chemistry surrounding vindoline [1] and its uses [2]. Of interest are the number of electron(s) involved in the electro-oxidation of its tertiary amine nitrogen and the dihydro-indole nitrogen. Normal pulse voltammetry (NPV) showed two successive one-electron removals respectively from the two nitrogens; essentially in conformity with reported work [3] based on a different technique. The second electron transfer likely is not reversible as reverse normal pulse voltammetry (RNPV) revealed no first current plateau [4] irrespective of the initial potential(s) selected from the second plateau of the normal pulse voltammogram. On the other hand, anodic cyclic voltammetry of vindoline [5] appears to indicate the formation of its dimers [5, 6] and trimers [7, 8]. [1] Inam ul Haque, Hina Saba, Vindoline and its reactions, Journal of the Chemical Society of Pakistan, 33 (6) 905-915 (2011) [2] Zhengqiong Zhang, Chengqi Lu, Pei Wang, Aijing Li, Hongbo Zhang, Sichuan Xu, Structural basis and mechanism for vindoline dimers interacting with α,β-tubulin, ACS Omega, 4 (7) 11938-11948 (2019) [3] Toivo Naaranlahti, Veli-Pekka Ranta, Pekka Jarho, Mervi Nordström, Seppo P. Lapinjoki, Electrochemical detection of indole alkaloids of Catharanthus roseus in high-performance liquid chromatography, The Analyst, 114 (10) 1229-1231 (1989) [4] C.L. Kulkarni, Barry J. Scheer, James F. Rusling, Potential-sweep and pulse voltammetric investigations of the anodic dimerization of tetrahydrocarbazoles, Journal of Electroanalytical Chemistry, 140 (1) 57–74 (1982) [5] Inam ul Haque, Voltammetric behaviour of meta-dimethylaminoanisidine at glassy carbon electrode, Journal of the Chemical Society of Pakistan, 12 (3) 256-259 (1990) [6] Ibro Tabakovic, Katmerka Tabakovic, One pot electrochemical synthesis of 10,10′-bisvindoline by an oxidation-reduction sequence, Tetrahedron Letters, 37 (21) 3659-3662 (1996) [7] Áron Szigetvári, András Keglevich, Péter Keglevich, Miklós Dékány, László Hazai, Csaba Szántay Jr, A mainly NMR-based structure elucidation of a surprising vindoline trimer with the aid of non-uniform sampled 1H-13C HSQC and HMBC spectra, Structural Chemistry, 30 (3) 795–804 (2019) [8] Kai Yu, Hong Zhang, Jing He, Richard N. Zare, Yingying Wang, Ling Li, Na Li, Dongmei Zhang, Jie Jiang, In situ mass spectrometric screening and studying of the fleeting chain propagation of aniline, Analytical Chemistry, 90 (12) 7154-7157 (2018)