Tabemaemontana bisindole

In addition to monomeric compounds, Tabemaemontana plants contain many bisindole alkaloids that are classified on the basis of constituent monomeric units, as in the extensive review by Cordell and Saxton in Volume XX of this series (14). This classification is more rational and comprehensive than others (I, 13, 15) and will be used as a guide for the representation of structural formulas and for the discussion of the chemistry of single alkaloids. 

The great number of different alkaloids found in Tabemaemontana precludes a discussion of the structure elucidation and chemistry of all of them. To keep the treatment concise, a major compromise was necessary. The alkaloids that have been reported in previous volumes of this treatise (as indicated in Table I) and their trivial modification will not be mentioned here. This compromise eliminates from the discussion well-established and long-known alkaloids that were isolated not only from Tabemaemontana but also from other genera. Moreover, the plumeran alkaloids isolated up to 1976 and ebuman-type and bisindole alkaloids isolated up to 1979 are covered in Volumes XVII and XX. The main efforts of this chapter will be focused on more recently isolated compounds, some of which are structurally and biogenetically relevant and have been found only in plants of the genus Tabemaemontana. 

Conoduramine occurs in the root bark of Tabemaemontana elegans, together with seven new bisindole alkaloids, tabernaelegantines A—D, tabernaelegantinines A and B, and tabernaelegantinidine. tabernaelegantines A—D are formulated as the two pairs of C-20 epimers (248)—(251), but the detailed evidence on which these structures are based is not yet available, ... 

Tabemaemontana corymbosa also provided several new bisindole alkaloids, conodiparines A-D (362-365) which are constituted from union of iboga and vobasinyl moieties [237]. The spectral data indicated that in conodiparines A (362) and C (364), the dimers are branched from C(3) of the vobasinyl unit to C(IO ) of the iboga unit whereas in conodiparines B (363) and D (365), the connection is from C(3) to C(12 ). The configuration of C( 19 ) in conodiparines A (362) and B (363) was determined to be 5 from examination of the carbon shifts of C(15 ) and C(2r) which corresponds to those of the iboga alkaloid heyneanine (345), exemplifying the 19(5) series in iboga alkaloids with a hydroxylethyl side chain [238]. 

R/S-Hydroxy-N4-demethyl ervahanine B (180) Bisindole Tabemaemontana dichotoma Bk, Rt bk 90,93... 

Conophyllidine (548) is identical in all respects with conophylline except for replacement of the epoxide function at positions 14 and 15 of the tabersonine epoxide unit by a double bond (333). Conophylhne has also been subsequently isolated from the South American species, Tabemaemontana glandulosa (336), and from the Thai species, Ervatamia microphylla (in all probabihty T. divaricatd) (337). It has also been reported from another Malaysian species, Ervatamia polyneura (T. dichotoma), under the name polyervine (338). The leaf extract of E. polyneura also yielded the related bisindole, polyervinine (549), which is similar to conophylline, except for the aromatic portion of the vincadifformine unit, which in the case of 549 incorporates an indoline dione chromophore, existing predominantly in its zwitterionic quinoniminium form. 

---