Separation and purification of constituents of the stem bark extract from Alstonia constricts yielded eight alkaloids. Some of these alkaloids had been previously isolated from the root bark of this species (alstonilidine, alstonidine, and O-3,4,5-trimethoxybenzoylquebrachidine), but others (vincamedine, 1-carbomethoxycarboline, and quebrachidine) had not. A new alkaloid, 14-ketoalstonidine [1], is described. Although the alkaloidal constituents of the root bark of Alstonia constricta F. Muell. (Apocynaceae) (1) have been known for many years, the stem bark appears not to have been investigated. We have now isolated eight alkaloids, one of them new, from this source. The separation scheme used was mainly dependent on the different polarity of the alkaloids in the various fractions. The ground bark after removal of lipid materials via hexane extraction was extracted with MeOH. The MeOH extract was extracted with 5% HCl, the aqueous acidic extract was basified with NH4OH, and the free bases were extracted from the aqueous basic extract first with Et2O and then CHCl3. The Et2O extract was further partitioned between buffer (pH 3) and CHCl3. The aqueous buffer extract was basified with NH4OH and extracted with CHCl3. The CHCl3 extract was separated by low pressure column chromatography into six fractions (A-F). TIC of these fractions showed that neither tetrahydroalstonine nor alstoniline was present. By gradient elution flash column chromatography (Si gel) of Fraction A and tlc of the subfractions, the known alkaloid, alstonilidine, was obtained, as well as a new alkaloid, identified as 14-ketoalstonidine [1]. 14-Ketoalstonidine, a labile, non-crystalline compound, was purified by flash column chromatography and preparative tlc. The uv absorption spectrum in EtOH (λ max 226, 292, 376 nm) suggested the presence of a carbonyl group conjugated to a harman nucleus. (2) The ir spectrum showed the presence of an O-H group (3220 cm-1), and strong bands at 1720, 1695, and 1635 cm-1 indicated the presence of two carbonyl groups and an enol ether double bond. The 1H-nmr spectrum of the new alkaloid was similar to that of alstonidine. The aromatic region was identical except that the C6-H signal was shifted downfield. The signals are assigned as follows (the chemical shifts shown in brackets are the corresponding ones in alstonidine). A one-proton doublet at δ 8.45 (8.39) (J5,6=5.0 Hz) is assigned to H-5, a one-proton doublet at δ 8.22 (7.91) (J6,5=5.0 Hz) is assigned to H-6, a one-proton broad doublet at δ 8.18 (8.80) (J9,10=7.8 Hz) is assigned to H-9, a one-proton octet at δ 7.67 (7.68) (J10,11=8.3, J10,9=7.8, J11,12=1.3 Hz) is assigned to H-10, a one-proton broad doublet at δ 7.52 (7.48) (J12,11=8.4 Hz) to H-12, a one-proton multiplet at δ 7.34 (J11,12=8.4, J11,10=8.3, J=1 Hz) to H-11, a one-proton singlet at δ 7.87 (7.69) to H-17, and a one-proton signal (d,d,d) at δ 4.63 (J19,20=10, J19-H,Me=6.3 Hz) to H-19. The methyl ester signal appeared as a singlet at δ 3.52 (3.44). A one-proton multiplet at δ 2.23 (2.22) is assigned to H-20. The 19-Me group appeared as a doublet at δ 1.40 (1.49) (J19-Me,19=6.4 Hz). Lamberton (2) reported that the signal from H-15 of alstonidine acetate was obscured by that of the methyl ester at δ 3.68. The new alkaloid gave a signal at δ 5.08 (doublet, J15,20=4.9 Hz) which we assigned to H-15. This represents a downfield shift relative to that in alstonidine acetate. The coupling constant, 4.9 Hz, is ascribed to a pseudo-cis relationship of H-15 and H-20. The signals at δ 3.80 and 3.36 are assigned to the two C21 hydrogens. The Hb-21 signal appeared as a doublet of doublets (Jgem=11.7 and JHb,H-20=4.2 Hz) at δ 3.80, and the Ha-21 signal appeared as a triplet (doublet of doublets, Jgem=JHa,20-H=11.7 Hz). The C21 hydrogens are not equivalent, owing, we believe, to an intramolecular hydrogen bonding between C21-OH and either the carbonyl group at C14 or Nb of the β-carboline nucleus. Therefore, restricted rotation was expected. From models the angle between H-20 and Ha-21 is 170°, and that between H-20 and Hb-21 is 40°. A high resolution mass spectrum showed the molecular ion peak at m/z 394.15329 (C21H22N2O5 requires 394.15288). Further support for the assigned structure for this alkaloid was shown by its fragmentation pattern in the mass spectrum as shown in Scheme 1. Vincamedine was separated from other subfractions of fraction A by column chromatography. The known alkaloid alstonidine, presumably the biogenetic precursor of the 14 keto-derivative, was crystallized from fraction B. Evaporation of the mother liquor of fraction B followed by flash column chromatography gave 1-carbomethoxy-β-carboline as a major alkaloid. A second alkaloid was separated by prolonged chromatography (flash column chromatography, tlc, and hplc), and identified as O-3,4,5-trimethoxybenzoylquebrachidine. Quebrachidine was separated from fraction C. 3,4,5-Trimethoxybenzamide was separated from the first set of fractions from the low pressure column chromatography of the CHCl3-soluble extract. It is likely that this compound is an artifact arising from 3,4,5-trimethoxybenzoylquebrachidine during processing of the alkaloidal extracts with NH4OH.