The Structure and Stereoisomerism of Three Mitragyna Alkaloids

Abstract

Isorhyncophylline, the isomer into which rhyncophylline is convertible, has been f o~~n d to occur in nature. Both bases are interconvertible. Isorhyncophylline on hydrolysis with dilute hydrochloric acid is converted to an aldehyde reducible to isorhy~~cophyllol. When the aldehyde is reduced in the Wolff-Icishner reaction, it is also isomerized and the product is isorhyncophyllane. This reduction product is oxidized by mercuric acetate to a neutral dilactam w h i~h still contains the oxindole carbonyl and further contains a new lactam carbonyl present in a six-membered ring. Reduction of the dilactam with lithium aluminum hydride gave a product having the spectroscopic properties of a n indole. This confirms the assumption previously made that in rhyncophylline, ring C is five-membered. The isomerization of rhyncophylline, mitraphylline, and formosanine is described. Formosanine has been shown t o be identical with uncarine-B and thus uncarine-A is the iso base derivable from formosanine.

Diastereomeric Spirooxindoles as Highly Potent and Efficacious MDM2 Inhibitors

“…Recyclization of a-TS affords four stereoisomers. 9 We did not attempt to determine the crystal structures of stereoisomers c and d because very limited amounts of the compounds could be obtained, due to their facile conversion to other isomers. Stereochemistry of isomers c and d were assigned based on the stability profiles of 5c and 5d in Figure 2 and the stereochemistry for isomers a and b .…”

Construction of Spiro[pyrrolidine‐3,3′‐oxindoles] − Recent Applications to the Synthesis of Oxindole Alkaloids

“…Wenkert and Marion both proposed a retro-Mannich reaction involving the open-ring intermediate 7. [6,7] Synthetically, the spiro[pyrrolidine-3,3Ј-oxindoles] core can be assembled by an intramolecular Mannich reaction. The precursors are available from tryptamine or a tryptophane-derived oxindole and an aldehyde.…”

Indole Alkaloids. XX. Isolation and Structural Elucidation of Four Minor Alkaloids from Voacanga Chalotiana Pierre Ex Stapf

“…1) It is well known that in acetic acid or pyridine solution the individual oxindole alkaloids corresponding to the seco and the hetero yohimbane type [16] undergo isomerization at carbon 7 and/or 3. This isomerization takes place through an iminium salt of the type represented in figure 4 [17]. In the case of voachalotine oxindole such an iminium structure (and therefore such an isomerization) is forbidden because of the bridgehead position of the NB nitrogen atom.…”