Synthesis and Evaluation of Paclitaxel-Loaded Gold Nanoparticles for Tumor-Targeted Drug Delivery.

The synthesis of a series of thiolated paclitaxel analogs is described as part of a novel nanomedicine program aimed at developing formulations of paclitaxel that will bind to gold nanoparticles for tumor targeted drug delivery. Preliminary evaluation of the new nanomedicine composed of 27 nm gold nanoparticles, tumor necrosis factor alpha (TNFα), thiolated polyethylene glycol (PEG-thiol), and one of several thiolated paclitaxel analogs is presented.

Furoquinoline Alkaloids and Methoxyflavones from the Stem Bark of Melicope madagascariensis (Baker) T.G. Hartley.

Melicope madagascariensis (Rutaceae) is an endemic plant species of Madagascar that was first classified as a member of the genus Euodia J. R. & G. Forst (Rutaceae) under the scientific name Euodia madagascariensis Baker. Based on morphological characteristics, Thomas Gordon Hartley taxonomically revised E. madagascariensis Baker to be M. madagascariensis (Baker) T.G. Hartley. Chemotaxonomical studies have long been used to help the identification and confirmation of taxonomical classification of plant species and botanicals. Aiming to find more evidences to support the taxonomical revision performed on E. madagascariensis, we carried out phytochemical investigation of two samples of the plant. Fractionation of the ethanol extracts prepared from two stem bark samples of M. madagascariensis (Baker) T.G. Hartley led to the isolation of seven known furoquinoline alkaloids 1-7 and two known methoxyflavones 8 and 9. The presence of furoquinoline alkaloids and methoxyflavones in the title species is in agreement with its taxonomic transfer from Euodia to Melicope. Antiprotozoal evaluation of the isolated compounds showed that 6-methoxy-7-hydroxydictamnine (heliparvifoline, 3) showed weak antimalarial activity (IC50 = 35 µM) against the chloroquine-resistant strain Dd2 of Plasmodium falciparum. Skimmianine (4) displayed moderate cytotoxicity with IC50 value of 1.5 µM against HT-29 colon cancer cell line whereas 3,5-dihydroxy-3',4',7-trimethoxyflavone (9) was weakly active in the same assay (IC50 = 13.9 µM).

Antiproliferative Triterpenoid Saponins from Leptaulus citroides Baill. from the Madagascar Rain Forest.

Bioassay-guided fractionation of EtOH extracts obtained from the roots and wood of the Madagascan plant Leptaulus citroides Baill. (Cardiopteridaceae) led to the isolation of ethyl esters of three new triterpenoid saponins (1-3) and the known sesquiterpenoid cinnamosmolide (4). The structures of 1-3 were elucidated by extensive 1D and 2D NMR experiments and mass spectrometry. Compounds 1, 2, and 4 showed moderate cytotoxicity against the A2780 human ovarian cancer cell line with IC50 values of 2.8, 10.2 and 2.0 µM, respectively.

Antiproliferative Diterpenes from a Malleastrum sp. from the Madagascar dry forest.

An ethanol extract of leaves of the plant species Malleastrum sp. collected in northern Madagascar afforded the new clerodane diterpene 18-oxo-cleroda-3,13-dien-16,15-olide (1), together with the three known clerodane diterpenes 16,18-dihydroxykolavenic acid lactone (2), solidagolactone (3) and (-)-kolavenol (4), and the known labdane diterpene 3-oxo-ent-Iabda-8(17),13-dien-15,16-olide (5). Compounds 1, 3, and 4 showed moderate antiproliferative activities against the A2780 ovarian cancer cell line, with the IC50 values of 3.01 ± 0.8, 7.84 ± 0.2, and 17.9 ± 3 µM, respectively. The structure elucidations of all compounds were carried out based on analysis of NMR and mass spectroscopic data. The relative stereochemistry of compound 1 was determined by NOESY NMR spectrum.

Antiproliferative and antiplasmodial compounds from selected Streptomyces species.

In continuation of our ongoing search for bioactive compounds from microbial extracts, we performed antiproliferative and/or antimalarial assays on extracts of 806 microbial species isolated from Madagascan marine organisms, on 1317 species isolated from Madagascan soil samples and on a Streptomyces species (S.4) from a marine sponge collected from the Florida Keys. This work identified active extracts from four Streptomyces isolates (S.1, S.2, S.3 and S.4). The extracts of Streptomyces S.1 and S.2 showed antiproliferative activity against the A2780 ovarian cancer cell line, while those of S.3 and S.4 displayed both antiproliferative and antimalarial activity. Bioassay-guided fractionation coupled with dereplication of the active extracts led to the identification and isolation of nonactin (1), monactin (2), dinactin (3), ±-nonactic acid (4), toyocamycin (5), piperafizine A (6) and a new dipeptide named xestostreptin (7). The structures of all isolated compounds 1-7 were elucidated by analyses of their NMR spectroscopic and mass spectrometric data, and were confirmed by comparison with the data reported in the literature. Compound 6 was crystallized and subjected to X-ray diffraction analysis to confirm its structure as piperafizine A (6). Compounds 1-3 displayed strong antiproliferative activity against A2780 ovarian cancer cells (IC50 values of 0.1, 0.13 and 0.2 µM, respectively), A2058 melanoma cells (IC50 values of 0.2, 0.02 and 0.02 µM, respectively), and H522-T1 non small-cell cancer lung cells (IC50 values of 0.1, 0.01 and 0.01 µM, respectively), while compounds 4 and 7 exhibited weak antiplasmodial activity against the Dd2 strain of Plasmodium falciparum, with IC50 values of 6.5 and 50 µM, respectively.

A Synthetic Butenolide Diterpene is now a Natural Product Isolated from Metaporana sericosepala, a Plant from the Madagascar Dry Forest.

Antiproliferative bioassay-guided fractionation of the ethanolic extract of the endemic Madagascan plant Metaporana sericosepala led to the first natural product isolation of a butenolide diterpene, which was synthesized during an anti-inflammatory study in 1988. The structure of the compound was elucidated as 3-homofarnesyl-4-hydroxybutenolide (1) by analysis of its spectroscopic data, including 1D- and 2D-NMR data and chemical evidence. The once synthetic compound can now also be considered as a natural product. Compound 1 had modest antiproliferative activity towards the A2780 ovarian cancer cell line,with an IC50 value of 8 µM.

Antiproliferative Trihydroxyalkylcyclohexenones from Pleiogynium timoriense.

Investigation of a DCM extract of the bark of Pleiogynium timoriense from the former Merck collection of natural product extracts for antiproliferative activity indicated that it was active with an IC50 value of 1.3 µg/mL against the A2780 ovarian cancer cell line. Bioassay-directed fractionation of this extract yielded the three new bioactive trihydroxyalkylcyclohexenones 1-3. Their structures were determined by a combination of spectroscopic and chemical methods. Compounds 1-3 exhibited submicromolar antiproliferative activity against the A2780 human ovarian cancer cell line, with IC50 values of 0.8, 0.7, and 0.8 µM, respectively.

Antiproliferative Compounds from Ocotea macrocarpa from the Madagascar Dry Forest1.

Bioassay-directed fractionation of an antiproliferative ethanol extract of the roots of Ocotea macrocarpa (Lauraceae) afforded the new butanolide macrocarpolide A (1), and the two new secobutanolides macrocarpolides B (2) and C (3), together with the known butanolides linderanolide B (4) and isolinderanolide (5). The structure elucidation of all compounds was carried out based on NMR and mass spectroscopic data analyses. The absolute configurations of all compounds isolated were determined by comparison of their optical rotation values with those found in literature. Compounds 1-5 showed good antiproliferative activities against the A2780 ovarian cell line, with IC50 values of 2.57 ± 0.12 (1), 1.98 ± 0.23 (2), 1.67 ± 0.05 (3), 2.43 ± 0.41 (4), and 1.65 ± 0.44 µM (5), respectively.

Antimalarial 5,6-Dihydro-α-pyrones from Cryptocarya rigidifolia: Related Bicyclic Tetrahydro-α-Pyrones Are Artifacts1.

Antimalarial bioassay-guided fractionation of an EtOH extract of the root wood of Cryptocarya rigidifolia (Lauraceae) led to the isolation of the five new 5,6-dihydro-α-pyrones cryptorigidifoliols A-E (1-5) and the six bicyclic tetrahydro-α-pyrone derivatives cryptorigidifoliols F-K (6-11). The structure elucidations of all compounds were made on the basis of the interpretation of spectroscopic data and chemical derivatization, and the relative and absolute configurations were determined by NOESY, electronic circular dichroism (ECD), and (1)H NMR analysis of α-methoxyphenylacetyl (MPA) derivatives. The bicyclic tetrahydro-α-pyrone derivatives were identified as products of acid-catalyzed intramolecular Michael addition of the 5,6-dihydro-α-pyrones in the presence of silica gel. A structure-activity relationship study suggested that the presence of an α,ß-unsaturated carbonyl moiety is not essential for potent antimalarial activity.

Antiproliferative Compounds from Cleistanthus boivinianus from the Madagascar Dry Forest.

The two new lignans 3α-O-(ß-D-glucopyranosyl)desoxypodophyllotoxin (1) and 4-O-(ß-D-glucopyranosyl)dehydropodophyllotoxin (2) were isolated from Cleistanthus boivinianus, together with the known lignans deoxypicropodophyllotoxin (3), (±)-ß-apopicropodophyllin (4), (-)-desoxypodophyllotoxin (5), (-)-yatein (6), and ß-peltatin-5-O-ß-D-glucopyranoside (7). The structures of all compounds were characterized by spectroscopic techniques. Compounds 1, 4, and 5 showed potent antiproliferative activities against the A2780 ovarian cancer cell line, with IC50 values of 33.0 ± 3.6, 63.1 ± 6.7, and 230 ± 1 nM, respectively. Compounds 2 and 7 showed only modest A2780 activities, with IC50 values of 2.1 ± 0.3 and 4.9 ± 0.1 µM, respectively, while compounds 3 and 6 had IC50 values of >10 µM. Compound 1 also had potent antiproliferative activity against the HCT-116 human colon carcinoma cell line, with an IC50 value of 20.5 nM, and compound 4 exhibited modest antiproliferative activity against the A2058 human caucasian metastatic melanoma and MES-SA human uterine sarcoma cell lines, with IC50 values of 4.6 and 4.0 µM, respectively.

Bioactive oleanane glycosides from Polyscias duplicata from the Madagascar dry forest.

As part of the International Cooperative Biodiversity Group (ICBG) program, in a search for antiproliferative compounds, an ethanol extract of Polyscias duplicata was investigated due to its antiproliferative activity against the A2780 human ovarian cell cancer line (IC50 6 µg/mL). Seven known oleanane glycosides, 3ß-[(α-L-arabinopyranosyl)oxy]-16α-hydroxyolean-12-en-28-oic acid (1, IC50 8 µM), 3ß-[(α-L-arabinopyranosyl)oxy]-16α,23-dihydroxyolean-12-en-18-oic acid (2, IC50 13 µM), 3ß-[(O-ß-D-glucopyranosyl-(t-->3)-α-L-arabinopyranosyl)oxy]-16α-hydroxyolean-12-en-28-oic acid (3, IC50 7 µM), 3ß-[(O-α-L-rhamnopyranosyl-(1-2)-α-L-arabinopyranosyl)oxy]-16α-hydroxyolean-12-en-28-oic acid (4, IC50 2.8 µM), 3ß-[(O-ß-D-glucopyranosyl-(l-->3)-α-L- arabinopyranosyl)oxy]-23-hydroxyolean-12-en-28-oic acid (5, IC50 10 µM), ß-[(O-α-L-rhamnopyranosyl-(-1.2)-α-L-arabinopyranosyl)oxy]-23-hydroxyolean-12-en-28-oic acid (6, IC50 3.4 µM), and 3ß-[(α-L-arabinopyranosyl)oxy]-23-hydroxyolean-12-en-28-oic acid (7, IC50 3.4 µM) were isolated, and their structures determined using spectroscopic methods.

Neolignans and other metabolites from Ocotea cymosa from the Madagascar rain forest and their biological activities.

Ten new neolignans including the 6'-oxo-8.1'-lignans cymosalignans A (1a), B (2), and C (3), an 8.O.6'-neolignan (4a), ococymosin (5a), didymochlaenone C (6a), and the bicyclo[3.2.1]octanoids 7-10 were isolated along with the known compounds 3,4,5,3',5'-pentamethoxy-1'-allyl-8.O.4'-neolignan, 3,4,5,3'-tetramethoxy-1'-allyl-8.O.4'-neolignan, didymochlaenone B, virologin B, ocobullenone, and the unusual 2'-oxo-8.1'-lignan sibyllenone from the stems or bark of the Madagascan plant Ocotea cymosa. The new 8.O.6'-neolignan 4a, dihydrobenzofuranoid 5a, and the bicyclo[3.2.1]octanoid 7a had in vitro activity against Aedes aegypti, while the new compounds 5a, 7a, 8, and 10a and the known virolongin B (4b) and ocobullenone (10b) had antiplasmodial activity. We report herein the structure elucidation of the new compounds on the basis of spectroscopic evidence, including 1D and 2D NMR spectra, electronic circular dichroism, and mass spectrometry, and the biological activities of the new and known compounds.

Antiproliferative and antimalarial sesquiterpene lactones from Piptocoma antillana from Puerto Rico.

Bioassay-directed fractionation of an antiproliferative ethanol extract of the leaves and twigs of Piptocoma antillana (Asteraceae) afforded two new goyazensolide-type sesquiterpene lactones named 5-O-methyl-5-epiisogoyazensolide (1) and 15-O-methylgoyazensolide (2), together with the known compounds 1-oxo-3,10-epoxy-8-(2-methylacr1 0-epoxy-8-(2-methylacryloxy)-l 5-acetoxygermacra-2,4, 11(1 3)-trien-6(12)-olide (3) and 5-epiisogoyazensolide (4). The structure elucidation of all compounds was carried out based on NMR and mass spectroscopic data analyses. The relative and absolute configurations of all the isolated compounds were determined from their CD and NOESY NMR spectra. Compounds 1-4 showed moderately potent antiproliferative activities against A2780 ovarian cancer cells, with IC50 values of 1.5 +0.5, 0.6 ± 0.3, 1.62 ± 0.05, and 1.56 ± 0.04 µM, respectively. They also displayed antimalarial activity against Plasmodiumfalciparum, with IC50 values of 6.2 05 22 ± 0.5, 2.2± 0.5, 8.0 ± 0.4, and 9.0 ± 0.6 µM, respectively.

Nitrogen-containing dimeric nor-multiflorane triterpene from a Turraea sp.

The new triterpene turranoic acid (1) and the new N-containing nor-triterpene turraenine (2), along with triptocallic acid B (3) and esculentoic acid (4) were isolated from leaves of a Turraea sp. Compounds 1-3 showed weak to moderate in vitro antiplasmodial activity against the chloroquine-resistant Plasmodium falciparum strain FCM29. Compound 1 also displayed weak cytotoxic activity against the nonsmall lung cancer cell line H522-T1 with an IC50 value of 16.4 µM.

Synthesis of isotopically labeled epothilones.

The epothilones, including epothilones B and D, are macrocyclic lactones, which have potent cytotoxicities and promote the polymerization of tubulin to mictotubules by binding to and stabilizing the tubulin polymer. They have a very similar mechanism of action to paclitaxel (Taxol®). The determination of the microtubule-binding conformation of the epothilones is an important piece of information in designing improved analogs for possible clinical use, and internuclear distance information that will assist the determination of this conformation can be obtained by rotational echo double resonance (REDOR) NMR studies of microtubule-bound epothilones with appropriate stable isotope labels. Analogs of epothilone B and epothilone D with [(2) H3 ] and [(19) F] labels were prepared from an advanced precursor for potential use in REDOR NMR studies to determine internuclear distances in tubulin-bound ligand.

Isolation of antiplasmodial anthraquinones from Kniphofia ensifolia, and synthesis and structure-activity relationships of related compounds.

Bioassay-guided separation of the South African plant Kniphofia ensifolia for antiplasmodial activity led to the isolation of two new anthraquinones, named kniphofiones A and B (3 and 4), together with three known bioactive anthraquinone monomers (1, 2 and 5), and four known bisanthraquinones (6-9). The structures of the two new compounds were elucidated based on analyses of their 1D and 2D NMR spectra and mass spectrometric data. The dimeric compounds 6 and 7 displayed the strongest antiplasmodial activity among all the isolated compounds, with IC50 values of 0.4 ± 0.1 and 0.2 ± 0.1 µM, respectively. The two new compounds displayed modest activities, with IC50 values of 26 ± 4 and 9 ± 1 µM, respectively. Due to the synthetic accessibility of the new compounds and the increased activity shown by the dimeric compounds, a structure-activity relationship study was conducted. As a result, one analogue of kniphofione B (4), the caffeic acid derivative of aloe-emodin, was found to have the highest activity among all the aloe-emodin derivatives, with an IC50 value of 1.3 ± 0.2 µM.

Bioactive compounds from Stuhlmannia moavi from the Madagascar dry forest.

Bioassay-directed fractionation of the leaf and root extracts of the antiproliferative Madagascar plant Stuhlmannia moavi afforded 6-acetyl-5,8-dihydroxy-2-methoxy-7-methyl-1,4-naphthoquinone (stuhlmoavin, 1) as the most active compound, with an IC50 value of 8.1 µM against the A2780 human ovarian cancer cell line, as well as the known homoisoflavonoid bonducellin (2) and the stilbenoids 3,4,5'-trihydroxy-3'-methoxy-trans-stilbene (3), piceatannol (4), resveratrol (5), rhapontigenin (6), and isorhapontigenin (7). The structure elucidation of all compounds was based on NMR and mass spectroscopic data, and the structure of 1 was confirmed by a single crystal X-ray analysis. Compounds 2-5 showed weak A2780 activities, with IC50 values of 10.6, 54.0, 41.0, and 74.0 µM, respectively. Compounds 1-3 also showed weak antimalarial activity against Plasmodium falciparum with IC50 values of 23, 26, and 27 µM, respectively.

A new bioactive diterpene glycoside from Molinaea retusa from the Madagascar dry forest.

In a continuing collaboration in a search for new antiproliferative compounds in Madagascar as part of an International Cooperative Biodiversity Group (ICBG), an ethanol extract of Molinaea retusa Radlk. (Sapindaceae) was investigated on the basis of its moderate antiproliferative activity against the A2780 human ovarian cancer cell line (IC50 16 microg/mL). One new compound, 2", 3", 4", 6'-de-O-acetylcupacinoside (1, IC50 15.4 microM) and two known compounds, cupacinoside (2, IC50 9.5 microM) and 6-de-O-acetylcupacinoside (3, IC50 10.9 microM), were isolated by bioassay-directed fractionation using liquid-liquid partitioning, column chromatography, and HPLC. Compounds 2 and 3 also had moderate antiplasmodial activities, with IC50 values of 4.0 and 6.4 microM, respectively, against Plasmodium falciparum, Dd2 strain. The structures were determined using spectroscopic methods.

Structure elucidation of antiproliferative bisbenzylisoquinoline alkaloids from Anisocycla grandidieri from the Madagascar dry forest.

Antiproliferative bioassay-guided fractionation of the ethanol extract of the stems of Anisocycla grandidieri led to the isolation of the known alkaloids stebisimine (1), (+)-1,2-dehydrotelobine (2), (+)-2'-norcocsuline (3) and puetogaline B (4). Herein, we report the full NMR assignments of all compounds and the X-ray crystallography of single crystals of compounds 1 and 3. Compounds 2 and 3 showed moderate antiproliferative activity against the A2780 human ovarian cancer cell line with IC50 values of 4.1 ± 0.3 and 2.7 ± 0.3 µM, respectively, and they also displayed selective activity toward the H460 (large cell lung cancer), MCF-7 (breast ductal carcinoma), and UACC-257 (melanoma) cell lines.