From the alkaloidal fractions of the West African plant Cryptolepis sanguinolenta (Asclepiadaceae), two alkaloids were purified: one was identified as the known indoloquinoline alkaloid cryptolepine [1], A second, novel alkaloid was shown to have an empirical formula of C34H24N4O based on exact mass measurement. Through the concerted application of a series of homonuclear and inverse-detected 2D nmr experiments, the structure of the second alkaloid was established as a spiro-nonacyclic alkaloid, cryptospirolepine. One portion of the structure of cryptospirolepine [2] may be biogenetically derived from cryptolepine [1],Cryptolepis sanguinolenta (Lindl.) Schlechter (Asclepiadaceae), a shrub indigenous to West Africa, has long been employed by Ghanaian traditional healers in the treatment of various fevers, including malaria (1). A root decoction has been used in the clinical therapy both of malaria and of urinary and upper respiratory tract infections by Oku Ampofo at the Centre for Scientific Research into Plant Medicine in Ghana since 1974 (1). The indoloquinoline alkaloid cryptolepine (5-methyl-5H-indolo-[3,2-¿}quinoline) [1] was first isolated from extracts of the roots of Cryptolepis triangularis N. E.Br., a species native to the Belgian Congo, by Clinquart in 1929 (2). Shortly thereafter, the alkaloid was again isolated from the same species by Delvaux (3). Quite paradoxically, cryptolepine had been synthesized some 20 years prior by Fichter and coworkers (4-6). Cryptolepine was isolated from a Nigerian sample of Cr. sanguinolenta in 1951 by Gellert et al. (7). Almost 30 years later, the alkaloid was isolated from a

The roots of the indigenous West African shrub Cryptolepis sanguinolenta have proved to be a rich source of indoloquinoline alkaloids. To date, all of the alkaloids isolated have been analogs of indolo[3, 2‐b]quinoline. We now wish to report examples of two new indoloquinoline alkaloids which differ in the fusion of the indole and quinoline rings. The first, cryptosanguinolentine, is an angular indolo[3, 2‐c]quinoline. The second, cryptotackieine, is a linear indolo[2, 3‐b]quinoline system. Both of these families of alkaloids are without precedent from C. sanguinolenta. The structures of both were established through the extensive use of inverse‐detected micro nmr methods.

Quantities of material required for structural analysis were reduced substantially following the introduction of 3 mm microinverse and microdual NMR probes in 1992. We now report the first very low-level results obtainable with a new 1.7 mm submicro-inverse-detection gradient or SMIDG NMR probe. Using this technology at 600 MHz, it was possible to fully characterize an 8% impurity contained in a 0. 55 &mgr;mol sample of cryptolepine (1) that had been standing in excess of 2 years since its initial isolation. The impurity was unequivocally identified as cryptolepinone (2) through the concerted interpretation of GHSQC, GHMBC, homonuclear TOCSY, and ROESY spectra in conjunction with APCI LC/MS and CID data acquired from a portion of the serial dilution solution used to prepare the NMR sample. Submicro-inverse-detection gradient probes offer the prospect of reducing still further the quantities of sample required for full characterization under favorable circumstances, making rare and potentially novel natural products amenable to structural determination. SMIDG NMR technology is equally applicable to a range of small samples requiring characterization such as isolated impurities from drug substances, isolates from drug degradation studies, and secondary metabolites.

Numerous indoloquinoline alkaloid structures have been identified from extracts of the West African plant Cryptolepis sanguinolenta. Recently, through the use of 2D NMR methods and cryogenic NMR probe technology in conjunction with computer-assisted structure elucidation (CASE) methods, the structures of some chemical degradation products of this family of alkaloids have also been reported. We now report the characterization of a novel indoloquinoline dimeric alkaloid, quindolinocryptotackieine, through the extensive utilization of CASE methods. The NMR data presented here were collected over a decade earlier before the elucidation of the structure was possible, since manual analysis did not present a conclusive structure, whereas CASE produced a series of structures from which the structure could be verified. The original mass spectrometric (MS) data collected for the sample were problematic. Contemporary MS data were instead recollected from remaining small quantities of this alkaloid using modern instrumentation. The re-collected data gave a usable molecular ion and several key fragment ions that were diagnostically useful.