Modulation of the multidrug-resistance phenotype by new tropane alkaloid aromatic esters from Erythroxylum pervillei

Alkaloids in Contemporary Drug Discovery to Meet Global Disease Needs

An overview is presented of the well-established role of alkaloids in drug discovery, the application of more sustainable chemicals, and biological approaches, and the implementation of information systems to address the current challenges faced in meeting global disease needs. The necessity for a new international paradigm for natural product discovery and development for the treatment of multidrug resistant organisms, and rare and neglected tropical diseases in the era of the Fourth Industrial Revolution and the Quintuple Helix is discussed.

Tropane alkaloids from the stem bark of Erythroxylum bezerrae

Six previously undescribed tropane alkaloids, designated as erythrobezerrines A-F, were isolated from the EtOH extract from the stem bark of Erythroxylum bezerrae Plowman. Their structures were elucidated based on the interpretation of the NMR and MS data and in some instances, confirmed by X-ray diffraction analysis. The cytotoxicity of the isolated compounds was evaluated against the cancer cell lines L929, PC-3, HCT-116, SNB-19 and NCI-H460, but only erythrobezerrine C showed moderate activity with IC₅₀ values of 3.38 and 5.43 μM for HCT-116 and NCI-H460, respectively.

Erythroxylum in Focus: An Interdisciplinary Review of an Overlooked Genus

The genus Erythroxylum contains species used by indigenous people of South America long before the domestication of plants. Two species, E. coca and E. novogranatense, have been utilized for thousands of years specifically for their tropane alkaloid content. While abuse of the narcotic cocaine has impacted society on many levels, these species and their wild relatives contain untapped resources for the benefit of mankind in the form of foods, pharmaceuticals, phytotherapeutic products, and other high-value plant-derived metabolites. In this review, we describe the current state of knowledge of members within the genus and the recent advances in the realm of molecular biology and biochemistry.

Selective Acetogenins and Their Potential as Anticancer Agents

The Kingdom Plantae has provided several successful drugs for the treatment of different diseases, including cancer, and continues to be a source of new possible therapeutic molecules. For example, the annonaceous acetogenins (AAs) are secondary metabolites found in the Annonaceae family, which are plants employed in traditional medicine for the treatment of cancer and various other diseases. These polyketides are inhibitors of Complex I in the respiratory chain of tumor cells, a process that is closely related to tumor metabolism, cell death, apoptosis, and autophagy. The goal of this review is to update readers on the role of the AAs as antitumor agents using in vitro and in vivo studies to demonstrate their importance in the area of oncology drug discovery. For this purpose, we performed a literature search in the PubMed scientific database using a range of keywords, including acetogenins and cancer, acetogenins antitumor activity, acetogenins and cytotoxicity, and acetogenins mechanism of action, among others. As a result, we found that the AAs are cytotoxic compounds that can induce apoptosis, cell cycle arrest, and autophagy in vitro, in addition to exhibiting tumor growth inhibition in vivo. The functional group related to their antineoplastic activity is suggested to be the mono or bis tetrahydrofuran ring accompanied by two or more hydroxy groups. The versatility of the AA bioactivity therefore renders them potential therapeutic agents for cancer treatment. It is therefore apparent that nature is worth further examination to aid in the discovery of more effective, accurate, and less harmful therapies in the fight against cancer.

Natural Products Mediated Targeting of Virally Infected Cancer

The role of viral infection in developing cancer was determined in the start of 20th century. Until now, 8 different virus-associated cancers have been discovered and most of them progressed in immunosuppressed individuals. The aim of the present study is to look into the benefits of natural products in treating virally infected cancers. The study focuses on bioactive compounds derived from natural sources. Numerous pharmaceutical agents have been identified from plants (vincristine, vinblastine, stilbenes, combretastatin, and silymarin), marine organisms (bryostatins, cephalostatin, ecteinascidins, didemnin, and dolastatin), insects (cantharidin, mastoparan, parectadial, and cecropins), and microorganisms (vancomycin, rhizoxin, ansamitocins, mitomycin, and rapamycin). Beside these, various compounds have been observed from fruits and vegetables which can be utilized in anticancer therapy. These include curcumin in turmeric, resveratrol in red grapes, S-allyl cysteine in allium, allicin in garlic, catechins in green tea, and β-carotene in carrots. The present study addresses various types of virally infected cancers, their mechanism of action, and the role of different cell surface molecules elicited during viral binding and entry into the target cell along with the anticancer drugs derived from natural products by targeting screening of bioactive compounds from natural sources.

Isolation, spectral characterization, molecular docking, and cytotoxic activity of alkaloids from Erythroxylum pungens O. E. Shulz

Stem bark, root bark, and leaf extracts of Erythroxylum pungens were subjected to phytochemical analysis. N,N-dimethyltryptamine (DMT) was isolated and characterized from E. pungens roots. This unprecedented result is remarkable since no indole alkaloid has been previously reported from Erythroxylaceae so far. Eleven known tropane alkaloids were identified by their mass spectra and 3-(2-methylbutyryloxy)tropan-6,7-diol as well as 3-(2-methylbutyryloxy)nortropan-6,7-diol were isolated and characterized based on mass spectrometry, ¹H, ¹³C, COSY, and NOESY NMR analysis. The complete NMR data are reported for the first time. Inverse Structure-based and Ligand-Based virtual screening were carried out to identify possible targets for 3-(2-methylbutyryloxy)tropan-6,7-diol. The level of cytotoxicity of this tropane alkaloid aliphatic ester was discrete with potencies on the order of 0.3-1.0 mg/mL and better results against HeLa (50% cell viability reduction). Otherwise, atropine (0.3 mg/mL), a Solanaceae tropane alkaloid, and DMT (0.5 mg/mL) from E. pungens roots impaired at 50% the cell viability against HeLa, SiHa, PC3, and 786-0. This study stimulates scientific investigation of the impact of edaphoclimatic features in a semi-arid environment on tropane alkaloid biosynthesis.

The Chemical Synthesis and Applications of Tropane Alkaloids

Tropanes are an important class of alkaloid natural products that are found in plants all over the world. These compounds can exhibit significant biological activity and are among the oldest known medicines. In the early 19th century, tropanes were isolated, characterized, and synthesized by notable chemical researchers. Their significant biological activities have inspired tremendous research efforts toward their synthesis and the elucidation of their pharmacological activity both in academia and in industry. In this chapter, which addresses the developments in this field since 1994, the focus is on the synthesis of these compounds, and several examples of sophisticated synthetic protocols involving both asymmetric and catalytic approaches are described. In addition, the structures of more than 100 new alkaloids are included as well as the applications and pharmacological properties of some tropane alkaloids.

Application of (4+3) cycloaddition strategies in the synthesis of natural products

This review summarizes the applications of (4+3) cycloadditions, both classical and formal, in the syntheses of natural products in the last two decades.

The Search for Anticancer Agents from Tropical Plants

Many of the clinically used anticancer agents in Western medicine are derived from secondary metabolites found in terrestrial microbes, marine organisms, and higher plants, with additional compounds of this type being currently in clinical trials. If plants are taken specifically, it is generally agreed that the prospects of encountering enhanced small organic-molecule chemical diversity are better if tropical rather than temperate species are investigated in drug discovery efforts. Plant collection in tropical source countries requires considerable preparation and organization to conduct in a responsible manner that abides by the provisions of the 1992 Rio Convention of Biological Diversity and the 2010 Nagoya Protocol on Access to Genetic Resources. Correct taxonomic identifications and enhanced procedures for processing and documenting plant samples when collected in often difficult terrain are required. Phytochemical aspects of the work involve solvent fractionation, known compound dereplication, preliminary in vitro testing, and prioritization, leading to "activity-guided fractionation", compound structure determination, and analog development. Further evaluation of lead compounds requires solubility, formulation, preliminary pharmacokinetics, and in vivo testing in suitable models. Covering the work of the authors carried out in two sequential multidisciplinary, multi-institutional research projects, examples of very promising compounds discovered from plants acquired from Africa, Southeast Asia, the Americas, and the Caribbean region, and with potential anticancer activity will be mentioned. These include plant secondary metabolites of the diphyllin lignan, cyclopenta[b]benzofuran, triterpenoid, and tropane alkaloid types.

Role of NO-cGMP pathway in ovine cervical relaxation induced by Erythroxylum caatingae Plowman

Erythroxylum caatingae Plowman has a myorelaxing effect on smooth muscle tissue. We investigated the effect of the crude ethanolic extract of E. caatingae Plowman (Ec-EtOH) on the contractility of the ovine cervix. In an isometric system, circular strips were subjected to 90mM potassium (K(+)) or 30μM carbamylcholine (CCh)-induced contraction. We then exposed the tissue to cumulative concentrations of Ec-EtOH (1-729 μg/ml). In other bath solutions, the tissues were exposed to l-NG-nitroarginine methyl ester (l-NAME; 100μM), l-NAME (100μM)+l-arginine (300μM), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, ODQ; 5μM), 4-aminopyridine (4-AP; 3mM), tetraethylammonium (TEA; 0.3mM), glybenclamide (1μM), atosiban (10μM) or verapamil (3μM), followed by the addition of Ec-EtOH (1-729 μg/ml). We also evaluated the effect of cervical Ec-EtOH infusion (2mg) on cervical contractility in vivo. Ec-EtOH decreased cervical contractility induced by K(+) or CCh, and 729 μg/ml Ec-EtOH decreased 85.4±5.1% the amplitude of basal contractility in vitro, with an EC50 of 17.9±3.7 μg/ml. This effect of Ec-EtOH was prevented by l-NAME or ODQ. l-arginine impaired the blunting effect of l-NAME on cervical relaxation caused by Ec-EtOH. However, the potassium channel blockers 4-AP, TEA, and glybenclamide did not modify this myorelaxation triggered by Ec-EtOH. Ec-EtOH also decreased acetylcholine-induced contractions in tissue preincubated with verapamil. In addition, Ec-EtOH decreased ovine cervical contractions in vivo. Thus, Ec-EtOH had a relaxant effect on ovine cervical contractions. This may involve the nitric oxide signal, mediated by cGMP cellular transduction, and be related to intracellular calcium sequestration.

P-glycoprotein inhibitors of natural origin as potential tumor chemo-sensitizers: A review

Resistance of solid tumors to treatment is significantly attributed to pharmacokinetic reasons at both cellular and multi-cellular levels. Anticancer agent must be bio-available at the site of action in a cytotoxic concentration to exert its proposed activity. P-glycoprotein (P-gp) is a member of the ATP-dependent membrane transport proteins; it is known to pump substrates out of cells in ATP-dependent mechanism. The over-expression of P-gp in tumor cells reduces the intracellular drug concentrations, which decreases the cytotoxicity of a broad spectrum of antitumor drugs. Accordingly, P-gp inhibitors/blockers are potential enhancer for the cellular bioavailability of several clinically important anticancer drugs such as, anthracyclines, taxanes, vinca alkaloids, and podophyllotoxins. Besides several chemically synthesized P-gp inhibitors/blockers, some naturally occurring compounds and plant extracts were reported for their modulation of multidrug resistance; however, this review will focus only on major classes of naturally occurring inhibitors viz., flavonoids, coumarins, terpenoids, alkaloids and saponins.

Chiral Resolution and Absolute Configuration of 3α,6β-Dicinnamoyloxytropane and 3α,6β-Di(1-ethyl-1H-pyrrol-2-ylcarbonyloxy)tropane, Constituents of Erythroxylum Species

Chiral resolution of (±)-3α,6β-dicinnamoyloxytropane (1) and (±)-3α,6β-di(1-methyl-1 H-pyrrol-2-ylcarbonyloxy)tropane (2), prepared by esterification of (±)-3α,6β-tropanediol (3), was achieved using an amylose-derived HPLC stationary phase and normal phase conditions. The corresponding vibrational circular dichroism (VCD) spectra provided the absolute configuration of the enantiomers as (-)-(3 R,6 R)-1, (+)-(3S,6S)- 1, (-)-(3 R,6 R)-2 and (+)-(3S,6S)- 2. In each case, characteristic VCD bands for the absolute configuration determination of the 3α,6β-tropandiol esters were observed. While the absolute configuration of natural 1, previously isolated from Erythroxylum hypericifolium, could not be established due to the lack of literature optical rotation values, that of catuabine E, previously isolated from E. vacciniifolium, is now assigned as (-)-(3 R,6 R)-2 by comparison with the optical rotation values of the prepared samples and the reported rotation of the natural product.

Antimicrobial, antiproliferative and proapoptotic activities of extract, fractions and isolated compounds from the stem of Erythroxylum caatingae plowman

In the study, we have examined the antitumor and antimicrobial activities of the methanol extract, the fractions, a fraction of total alkaloids and two alkaloids isolated from the stem of Erythroxylum caatingae Plowman. All test fractions, except the hexane fractions, showed antimicrobial activity on gram-positive bacteria and fungi. The acetate: methanol (95:5), acetate, chloroform and hexane fractions show the highest cytotoxicity activity against the NCI-H292, HEp-2 and K562 cell lines using MTT. The absence of hemolysis in the erythrocytes of mice was observed in these fractions and 6β-Benzoyloxy-3α-(3,4,5- trimethoxybenzoyloxy) tropane (catuabine B). Staining with Annexin V-FITC and JC-1 was used to verify the mechanism of action of the compounds of E. caatingae that showed cytotoxicity less than 30 μg/mL in leukemic cells. After 48 h of incubation, we observed that the acetate: methanol (95:5), acetate, and chloroform fractions, as well as the catuabine B, increased in the number of cells in early apoptosis, from 53.0 to 74.8%. An analysis of the potential of the mitochondrial membrane by incorporation of JC-1 showed that most cells during incubation of the acetate: methanol (95:5) and acetate fractions (63.85 and 59.2%) were stained, suggesting the involvement of an intrinsic pathway of apoptosis.

Reversal of multidrug resistance by morning glory resin glycosides in human breast cancer cells

Reversal of multidrug resistance (MDR) by thirty resin glycosides from the morning glory family (Convolvulaceae) was evaluated in vinblastine-resistant human breast carcinoma cells (MCF-7/Vin). The effects of these amphipathic compounds on the cytotoxicity and P-glycoprotein (P-gp)-mediated MDR were estimated with the sulforhodamine B colorimetric assay. Active noncytotoxic compounds exerted a potentiation effect of vinblastine susceptibility by 1- to over 1906-fold at tested concentrations of 5 and 25 μg/mL. Murucoidin V (1) enhanced vinblastine activity 255-fold when incorporated at 25 μg/mL and also, based on flow cytometry, significantly increased the intracellular accumulation of rhodamine 123 with the use of reserpine as a positive control for a MDR reversal agent. Incubation of MCF-7/Vin cells with 1 caused an increase in uptake and notably lowered the efflux rate of rhodamine 123. Decreased expression of P-glycoprotein by compound 1 was detected by immunofluorescence flow cytometry after incubation with an anti-P-gp monoclonal antibody. These results suggest that resin glycosides represent potential efflux pump inhibitors for overcoming MDR in cancer therapy.

The relevance of higher plants in lead compound discovery programs

Along with compounds from terrestrial microorganisms, the constituents of higher plants have provided a substantial number of the natural product-derived drugs used currently in Western medicine. Interest in the elucidation of new structures of the secondary metabolite constituents of plants has remained high among the natural products community over the first decade of the 21st century, particularly of species that are used in systems of traditional medicine or are utilized as botanical dietary supplements. In this review, progress made in the senior author's laboratory in research work on naturally occurring sweeteners and other taste-modifying substances and on potential anticancer agents from tropical plants will be described.

Tropane alkaloids from Erythroxylum genus: distribution and compilation of 13C-NMR spectral data

Erythroxylum, the most representative genus of the Erythroxylaceae family, presents tropane alkaloids as main constituents. This class of compounds greatly contributes to the chemotaxonomic characterization of plants of this genus, and it has important medical uses and shows toxic effects. This review describes 186 tropane alkaloids in the 35 species of Erythroxylum distributed worldwide. In addition, a compilation of their (13)C-NMR spectral data is presented.

Absolute configuration determination and conformational analysis of (-)-(3S,6S)-3alpha,6beta-diacetoxytropane using vibrational circular dichroism and DFT techniques

The absolute configuration of semisynthetic (-)-3alpha,6beta-acetoxytropane 1, prepared from (-)-6beta-hydroxyhyoscyamine 2, has been determined using vibrational circular dichroism (VCD) spectroscopy. The vibrational spectra (IR and VCD) were calculated using DFT at the B3LYP/DGDZVP level of theory for the eight more stable conformers which account for 99.97% of the total relative abundance in the first 10 kcal/mol range. The calculated VCD spectra of all considered conformations showed two distinctive spectral ranges, one between 1300 and 1200 cm(-1), and the other one in the 1150-950 cm(-1) region. When compared with the experimental VCD spectrum, the first spectral region confirmed the calculated conformational preferences, whereas the second region showed little change with conformation, thus allowing the determination of the absolute configuration of 1 as (3S,6S)-3alpha,6beta-diacetoxytropane. Also, the bands in the second region showed similarities between 1 and 2 in both the experimental and calculated VCD spectra, suggesting that these bands are mainly related to the absolute configuration of the rigid tropane ring system, since they show conformational independency, no variations with the nature of the substituent, and are composed by closely related vibrational modes.

Absolute configuration of tropane alkaloids from Schizanthus species by vibrational circular dichroism

The absolute configuration (AC) of 6beta-hydroxy-3alpha-senecioyloxytropane (1), 3alpha-hydroxy-6beta-tigloyloxytropane (2), 3alpha-hydroxy-6beta-senecioyloxytropane (3), and 3alpha-hydroxy-6beta-angeloyloxytropane (4) was assigned as (1R,3R,5S,6R) using density functional theory (DFT) calculations at the B3LYP/DGDZVP level of theory in combination with experimental vibrational circular dichroism (VCD) measurements and comparison with the spectra of similar tropanes. The AC of 1 followed from a sample isolated from Schizanthus grahamii, while those of the mixture of 2 and 3, isolated from the same source, were determined by comparing the VCD measurement to a weighted calculation of the individual VCD spectra according to a 69:31 ratio of 2:3 determined by (1)H NMR signal integration. In turn, Schizanthus pinnatus provided a 7:3 mixture of 1:4 whose AC was determined using the experimental VCD absorptions in the 1150-950 cm(-1) spectral region which were compared with those observed for 1-3 and with those described for other 3alpha,6beta-tropanediol derivatives.

Two New Tropane Alkaloids from the Bark of Erythroxylum vacciniifolium Mart. (Erythroxylaceae)

Two new tropane alkaloid N-oxides substituted by a methylpyrrole moiety were isolated from the bark of Erythroxylum vacciniifolium Mart. (Erythroxylaceae), a Brazilian indigenous plant, locally known as catuaba and used in traditional medicine as an aphrodisiac. The alkaloid structures were determined by a combination of high resolution mass spectrometry and multi-dimensional NMR spectroscopy.

Evaluation of the cholinergic and adrenergic effects of two tropane alkaloids from Erythroxylum pervillei

Pervilleine A is an aromatic ester tropane alkaloid from Erythroxylum pervillei that has shown promising activity as a multidrug resistance inhibitor. Due to its structural similarity with the well known (-)-hyoscyamine and (-)-cocaine, the cholinergic and adrenergic activities of pervilleine A were evaluated. At 30 microm (+/-)-pervilleine A hydrochloride exhibited non-competitive inhibition of the cholinergic response in the guinea-pig ileum and did not affect the carbachol-induced contraction of the rat anococcygeus smooth muscle. (+/-)-Pervilleine A hydrochloride blocked nonspecifically the vascular response of (-)-norepinephrine in the rat aorta ring, while the contractile response of rat vas deferens to (-)-norepinephrine was not affected significantly at a 100 microm concentration. An analogue of pervilleine A, (+/-)-pervilleine H, without a 6-O-trans-3,4,5-trimethoxycinnamoyl ester substituent required for anti-multidrug resistance activity, did not exhibit any effects in these experiments. The data suggest that (+/-)-pervilleine A hydrochloride has weak nonspecific anticholinergic and vascular antiadrenergic activities. The lack of significant cholinergic and adrenergic receptor-mediated activities may be considered advantageous for the further development of pervilleine A as a new adjuvant in cancer chemotherapy.

Relationships between inhibitory activity against a cancer cell line panel, profiles of plants collected, and compound classes isolated in an anticancer drug discovery project

In an attempt to determine the relationships between the plant profiles (country of collection, taxonomy, plant part) and the compound classes isolated with cytotoxic activity against a panel of human tumor cell lines, the data compiled from a 15-year anticancer drug-discovery project were subjected to an analysis of variance (ANOVA). The results indicate significant trends in cytotoxic activity relative to collection location, taxonomy, plant part, and compound classes isolated. Plant collections were made in tropical forests in six countries, with collections from Ecuador resulting in higher activity than those from Indonesia and Peru. Interestingly, collections from Florida were not statistically different than those from the countries with higher biodiversity. One hundred and forty-five families were represented in the collections, with the Clusiaceae, Elaeocarpaceae, Meliaceae, and Rubiaceae having low ED50 (half maximal effective dose) values. Especially active genera included Aglaia, Casearia, Exostema, Mallotus, and Trichosanthes. Roots and below-ground plant materials were significantly more active than above-ground materials. Cucurbitacins, flavaglines, anthraquinones, fatty acids, tropane alkaloids, lignans, and sesquiterpenoids were significantly more active than xanthones and oligorhamnosides. The results from this study should serve as a guide for future plant collection endeavors for anticancer drug discovery.

Tropane aromatic ester alkaloids from a large-scale re-collection of Erythroxylum pervillei stem bark obtained in Madagascar

Fractionation by pH zone-refining countercurrent chromatography of an extract of the stem bark of Erythroxylum pervillei, obtained on a kilogram scale in southern Madagascar, led to the isolation and characterization of four tropane aromatic ester alkaloids as minor constituents, namely, pervilleines G (5) and H (6) and cis-pervilleines B (7) and F (8). Their structures were determined by spectroscopic data interpretation.

ABC transporters as multidrug resistance mechanisms and the development of chemosensitizers for their reversal

One of the major problems related with anticancer chemotherapy is resistance against anticancer drugs. The ATP-binding cassette (ABC) transporters are a family of transporter proteins that are responsible for drug resistance and a low bioavailability of drugs by pumping a variety of drugs out cells at the expense of ATP hydrolysis. One strategy for reversal of the resistance of tumor cells expressing ABC transporters is combined use of anticancer drugs with chemosensitizers. In this review, the physiological functions and structures of ABC transporters, and the development of chemosensitizers are described focusing on well-known proteins including P-glycoprotein, multidrug resistance associated protein, and breast cancer resistance protein.

Drug discovery from medicinal plants

Current research in drug discovery from medicinal plants involves a multifaceted approach combining botanical, phytochemical, biological, and molecular techniques. Medicinal plant drug discovery continues to provide new and important leads against various pharmacological targets including cancer, HIV/AIDS, Alzheimer's, malaria, and pain. Several natural product drugs of plant origin have either recently been introduced to the United States market, including arteether, galantamine, nitisinone, and tiotropium, or are currently involved in late-phase clinical trials. As part of our National Cooperative Drug Discovery Group (NCDDG) research project, numerous compounds from tropical rainforest plant species with potential anticancer activity have been identified. Our group has also isolated several compounds, mainly from edible plant species or plants used as dietary supplements, that may act as chemopreventive agents. Although drug discovery from medicinal plants continues to provide an important source of new drug leads, numerous challenges are encountered including the procurement of plant materials, the selection and implementation of appropriate high-throughput screening bioassays, and the scale-up of active compounds.

Methylpyrrole tropane alkaloids from the bark of Erythroxylum vacciniifolium

Nine new tropane alkaloids substituted by a methylpyrrole moiety were isolated from the bark of Erythroxylum vacciniifolium, a Brazilian endemic plant used in traditional medicine and locally known as catuaba. All compounds were elucidated as tropanediol or -triol alkaloids esterified by at least one 1-methyl-1H-pyrrole-2-carboxylic acid. One of the isolated compounds was identified as a tropane alkaloid N-oxide. Their structures were determined by high-resolution mass spectrometry and multidimensional NMR spectroscopy.

On-line identification of tropane alkaloids from Erythroxylum vacciniifolium by liquid chromatography–UV detection–multiple mass spectrometry and liquid chromatography–nuclear magnetic resonance spectrometry

The bark of catuaba (Erythroxylum vacciniifolium Martius, Erythroxylaceae), a tree native to the northern part of Brazil, was investigated for its alkaloid content. With the aim of obtaining preliminary structure information on-line, the alkaloid extract was analysed by high-performance liquid chromatography coupled to diode array UV detection, to mass spectrometry and to nuclear magnetic resonance. Interpretation of on-line spectroscopic data obtained from this extract led to structural elucidation of six new alkaloids and partial identification of 18 potentially original alkaloids bearing the same tropane skeleton esterified in positions 3 and 6 by 1-methyl-1H-pyrrol-2-carboxylic acid and/or 4-hydroxy-3,5-dimethoxybenzoic acid.

Tropane alkaloids from the bark of Erythroxylum vacciniifolium

Eight new tropane alkaloids (1-8) were isolated from the bark of "catuaba", a Brazilian endemic plant Erythroxylum vacciniifolium Martius. Their structures were determined by high-resolution mass spectrometry and multidimensional NMR spectroscopy.

Pervilleines B and C, new tropane alkaloid aromatic esters that reverse the multidrug-resistance in the hollow fiber assay

P-Glycoprotein (Pgp)-mediated drug efflux can yield a multidrug-resistance phenotype that is associated with poor response to cancer chemotherapy. Pervilleines B and C (PB and PC), two new tropane alkaloid aromatic esters obtained from a chloroform extract of the roots of Erythroxylum pervillei as the result of bioactivity-guided fractionation, were found to restore the vinblastine (VLB) sensitivity of cultured multidrug-resistant KB-V1 cells, with 50% inhibitory concentration values of 0.17 microM in each case. To explore the potential relevance of this response, KB-V1 cells were placed in hollow fibers and implanted into NCr nu/nu mice. Cell growth was not significantly inhibited when VLB or PB or PC were administered as single agents, but when used in combination with vinblastine inhibition of up to 77.7% was observed. Equimolar doses of verapamil were less effective. These data suggest that PB and PC are effective inhibitors of Pgp and should be further evaluated for clinical utility.

Reversal of multidrug resistance by tropane alkaloids from the stems of Erythroxylum rotundifolium

Six tropane alkaloid esters were isolated from the stems of Erythroxylum rotundifolium. The structures of three new tropane esters, 7beta-hydroxy-6beta-(3,4,5-trimethoxybenzoyloxy)-3alpha-(E)-(3,4,5-trimethoxycinnamoyloxy)tropane (1), 6beta-benzoyloxy-3alpha-(Z)-(3,4,5-trimethoxycinnamoyloxy)tropane (2), and (-)-6beta-benzoyloxy-3alpha-hydroxytropane (3), were established by spectroscopic techniques. When alkaloids 1-6 were evaluated against a panel of human cancer cell lines, the new compound 6beta-benzoyloxy-3alpha-(Z)-(3,4,5-trimethoxycinnamoyloxy)tropane (2) and three known compounds, 6beta-benzoyloxy-3alpha-(3,4,5-trimethoxycinnamoyloxy)tropane (4), 6beta-benzoyloxy-3alpha-(E)-(3,4,5-trimethoxycinnamoyloxy)tropane-7beta-ol (5), and 7beta-acetoxy-6beta-benzoyloxy-3alpha-(E)-(3,4,5-trimethoxycinnamoyloxy)tropane (6), demonstrated greatest activity with multidrug-resistant oral epidermoid carcinoma (KB-V1) cells incubated in the presence of vinblastine. Thus, tropane esters of this type can reverse the multidrug-resistance phenotype, presumably by interacting with P-glycoprotein.