Structure Elucidation and Chemistry of Catharanthus Alkaloids III: Structure of Leurosine, an Active Anticancer Alkaloid

Catharanthus Alkaloids XXXIII. 21'-Oxo-Leurosine From Catharanthus Roseus (Apocynaceae)

“…A molecular ion at m/e 822 analyzed for C^eH.-iNíOio indicated the isolate contained an additional oxygen atom and two less hydrogens than leurosine (1). In addition, the mass spectrum displayed a number of ions typical of the presence of a vindoline moiety, particularly the ion at m/e 282 (3) (21).…”

Structure elucidation of indole–indoline type alkaloids: A retrospective account from the point of view of current NMR and MS technology

“…1) was discussed on the basis of 1 H, COSY and NOESY data. The overall conclusion was that the loss of the OH function and the epimerization of C (20 ) resulted only in a slight change in the conformation as compared to that described for VLB. The piperidine ring in this structure shifted from being half-chair towards a boat conformation.…”

“…1) enabled its exact stereochemical description [61]. In this compound the C(15 ) OH was suggested to be in the ␣ position on the basis of the strong ␥-effect observed on C(3 ), C(17 ), C (19 ) and C (21 ), and on the ␤-effect observed on C (14 ) and C (20 ). In possession of this information it is interesting to note that in the latest European Pharmacopoeia 7.0 [62] the configuration of the C(15 ) stereogenic centre is not specified for the analogous VCR impurity, C(15 ) OH VCR (impurity A).…”

“…1). Since LEU was derived from VLB, and VLB has a C(20 )-␤-OH group, it was incorrectly suggested as a seemingly plausible scenario that in LEU the epoxy-ring bridging the C(15 ) C(20 ) moiety was in the ␤ position [20]. Making use of the spectral data observed for LEU, on the basis of low-resolution 1 H and 13 C NMR data the structure of C(21 )-oxo-LEU was described improperly [26] as well.…”

“…1) were also evaluated in detail, and the derived data were used later for the structure elucidation of some new bisindole alkaloids [20]. Making use of the above described phenomenon observed for VLB, the m/z 808 ion peak was suggested as originating from the molecular ion from several other ion peaks (m/z 822 and 836, differing in CH 2 units), obtained from high-resolution MS measurements.…”