221. The constitution of aspidospermine. Part III. Reactivity at the nitrogen atoms, and biogenetic considerations

Abstract

Aspidospermine methiodide and deacetyl-N-methylaspidospermine dimethiodide have been prepared, and the nature of deacetyl-N-methylaspidospermine monomethiodide has been established. Thermodynamic dissociation constants of aspidospermine and several derivatives are recorded. A tentative structure for aspidospermine is discussed from the biogenetic aspect. ASPIDOSPERMINE (Ia) does not react with methyl iodide at room temperature,l and previous attempts to prepare a methiodide at elevated temperature have resulted only in ill-defined, amorphous products. However, a crystalline methiodide (IIa) has now been obtained by prolonged interaction of the components at 56". The rather sluggish reactivity of the basic nitrogen atom, N(b), is most probably due to steric hindrance, since its basic strength (see Table ) is comparable with that of strychnine, for example, which reacts readily with methyl iodide.

Evidence for a Transient Additional Ligand Binding Site in the TAS2R46 Bitter Taste Receptor

“…Strychnine has a pK a of 8.25. 40 It was therefore considered protonated, with a total charge +1. The molecule was docked on the final protein model using HADDOCK 2.1.…”

Determination of ionization constants of alkaloids by paper electrophoresis

“…Buffer solutions of ionic strength µ 0.01 covering the pH range [2][3][4][5][6][7][8][9][10][11] were prepared from standard solutions of hydrochloric acid, potassium chloride, potassium acid phthalate, potassium dihydrogen phosphate, sodium hydroxide, and sodium borate. Paper Electrophoretic Procedure.…”

247. Zur Chemie des Beninins und des Vobtusins

“…8). Substraktion des Spektrums von 6, 7-Dehydro-aspidospermidin vom Spektrum des Tetrahydro-anhydrovobtusins (13) gibt cine Kurve, die ahnlich dem Spektrum von N~,,-Desacetyl-Ni,,-methyl-aspidospermin [12] ist ( Fig. 8 (216 u) ist typisch fur 2,3-Dihydrovincadifformin [9].…”

“…Cf. N(,)-Mcthyl-desacetylaspidospermin [12] : Imnx 265 (3,85), 305 (3,40) ; I,7zin 242 (3,50) , 288 ( 3 , 3 2 ) . Uiffercnzspektrum von Vobtusin in konz.…”