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J. Nat. Prod. 1999, 62, 976-983
Synthesis and Biological Evaluation of Analogues of Cryptolepine, an Alkaloid Isolated from the Suriname Rainforest1 Shu-Wei Yang,† Maged Abdel-Kader,† Stan Malone,‡ Marga C. M. Werkhoven,§ Jan H. Wisse,⊥ Isia Bursuker,| Kim Neddermann,| Craig Fairchild,∇ Carmen Raventos-Suarez,∇ Ana T. Menendez,∇ Kate Lane,∇ and David G. I. Kingston*,† Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0212, Conservation International Suriname, Burenstrasse 7, Paramaribo, Suriname, The National Herbarium of Suriname, P.O. Box 9212, Paramaribo, Suriname, Bedrijf Geneesmiddelen Voorziening Suriname, Commissaris Roblesweg 156, Geyersluit, Suriname, Bristol-Myers Squibb Pharmaceutical Research Institute, 5 Research Parkway, Wallingford, Connecticut 06492-7660, and Bristol-Myers Squibb Pharmaceutical Research Institute, P.O. Box 4000, Princeton, New Jersey 05843 Received February 1, 1999
Bioassay-guided fractionation of an extract of a mixture of Microphilis guyanensis and Genipa americana collected in the rainforest of Suriname yielded the known alkaloid cryptolepine (2) as the major active compound in a yeast bioassay for potential DNA-damaging agents; the same compound was later reisolated from M. guyanensis. The structure of cryptolepine was identified unambiguously by spectral data and by its total synthesis. Several cryptolepine derivatives (3-29, 32-41) were synthesized based on modifications of the C-2, N-5, N-10, and C-11 positions. Two cryptolepine dimers (30, 31) were also prepared. The structure modifications did not result in compounds with a higher potency than the parent compound cryptolepine in the yeast assay system, although some derivatives did show significant activity. Selected compounds (6, 7, 17, 22, 23, 26, and 27) were also tested for cytotoxicity in mammalian cell culture, and two compounds showed significant cytotoxic activity. In continuation of our search for anticancer and other bioactive agents from the Suriname rainforest,2 an extract of a mixture of Microphilis guyanensis (A. DC) Pierre (Sapotaceae) and Genipa americana L. (Rubiaceae) collected on an ethnobotanical basis near Asindopo village in the rain forest of Suriname3 was found to show strong but nonselective activity in a yeast bioassay utilizing mutants 1138, 1140, and 1353 of the yeast Saccharomyces cerevisiae.4 In this assay system, general DNA-damaging agents and antifungal agents show activity against all three strains.2 This extract was thus selected for further investigation. Results and Discussion Isolation Studies. Bioassay-guided fractionation of the extract was carried out using a combination of column chromatography with Sephadex LH-20 and MCI gel to yield compound 1 as the major active component. Once the salt nature of 1 became clear it was obtained more efficiently by an acid-base partition using methods described in the literature,5 followed by further purification by chromatography on LH-20. The structure of compound 1 was assigned as cryptolepine hydrochloride by NMR techniques and HRFABMS, and its anion was determined as chloride using negativeion FABMS (Cl- ) m/z 35, 37). The 1H and 13C NMR resonances for 1 were assigned unambiguously by spectral data including 1H-1H COSY, HMBC, HMQC, and ROESY spectra, and are listed in the Experimental Section; most NMR data are reported for the free base cryptolepine (2) * To whom enquiries should be addressed. Tel.: (540) 231-6570. Fax: (540) 231-7702. E-mail:
[email protected]. † Virginia Polytechnic Institute and State University. ‡ Conservation International, Suriname. § National Herbarium of Suriname. ⊥ Bedrijf Geneesmiddelen Voorziening Suriname. | Bristol-Myers Squibb Pharmaceutical Research Institute, Wallingford. ∇ Bristol-Myers Squibb Pharmaceutical Research Institute, Princeton.
10.1021/np990035g CCC: $18.00
instead of its hydrochloride 1. The free base form of compound 1 was identified as cryptolepine (2) by comparison of its 1H NMR data with literature data. Compound 1 was active in the 1138, 1140, and 1353 yeast strains, with IC12 values of 0.6 µg/mL in each strain. It was also cytotoxic to the M109 cell line, with an IC50 of
