Discovery of betulinic acid as a selective inhibitor of human melanoma that functions by induction of apoptosis.

As a result of bioassay-guided fractionation, betulinic acid, a pentacyclic triterpene, was identified as a melanoma-specific cytotoxic agent. In follow-up studies conducted with athymic mice carrying human melanomas, tumour growth was completely inhibited without toxicity. As judged by a variety of cellular responses, antitumour activity was mediated by the induction of apoptosis. Betulinic acid is inexpensive and available in abundant supply from common natural sources, notably the bark of white birch trees. The compound is currently undergoing preclinical development for the treatment or prevention of malignant melanoma.

Prediction of human absorption of natural compounds by the non-everted rat intestinal sac model.

A major concern in natural drug research is that many substances with potent biological activity in vitro are unable to generate good activity in vivo owing to their poor water-solubility, poor permeability and/or poor stability. The permeability of drug candidates across the intestinal mucosa is one of the most important factors in defining drug bioavailability and biological activity. In order to screen promising compounds for further investigation, a non-everted rat intestinal sac model has been developed successfully to assay the permeability of natural compounds and to predict their human absorption. In this system, the drug solution was placed in non-everted intestinal sacs (NEIS), which were placed in an acceptor solution and the permeability of drug across intestine walls was determined. The feasibility of this method has been validated and demonstrated for 11 model compounds chosen from currently marketed drugs whose human fraction absorbed (Fa) data have been reported. The results of the studies indicate that a good relationship exists between the permeability of the model drugs and their corresponding Fa data. The permeability of 13 natural compounds was evaluated using this system. Only fraxinellone and vitexin-7-glucoside exhibited high intestinal permeability, and predictive of excellent human absorption, which awaits confirmation from further investigation in vivo. This model provides an alternative method to everted intestinal sacs for the evaluation of in vitro permeability in rats, and for estimating human absorption of drugs. It may therefore hold great promise for oral absorption screening of new drug candidates.

Biodiversity and drug discovery--a symbiotic relationship.

The profound developments in natural products drug discovery in the past few years are discussed, and the importance of a global approach to biodiversity and drug discovery involving natural products for the early part of the 21st century is presented.

Constituents of Afzelia bella stem bark.

The stembark of Afzelia bella yielded an acylated dihydroflavonol glycoside identified as 2R,3R-trans-aromadendrin-7-O-beta-D-glucopyranoside-6''-(4''-hydroxy-2''-methylene butanoate), along with five known flavonoids and the lignan glycoside (+)-isolariciresinol 9-O-xyloside. Their structures were determined by detailed 1D and 2D NMR analyses.

De-O-ethylsalvonitin and salprionin, two further diterpenoids from Salvia prionitis.

From Salvia prionitis two new diterpenoids, de-O-ethylsalvonitin and salprionin, were isolated, and their structures and NMR data were assigned by spectral analysis and computer modelling calculations.

Saikosaponin derivatives from Bupleurum wenchuanense.

From the roots of Bupleurum wenchuanense 14 derivatives of saikosaponin were isolated and identified as 2"-O-beta-D-xylopyranosylsaikosaponin b2, 3",6"-O O-diacetylsaikosaponin b2, 2"-O-beta-D-glucopyranosylsaikosaponin b2, saikosaponin b2, 6"-O-acetylsaikosaponin b2, saikosaponin d, 2"-O-acetylsaikosaponin d, 3"-O-acetylsaikosaponin d,6"-O-acetylsaikosaponin d, 16-epichikusaikoside, prosaikogenin G, saikosaponin a,2"-O-acetylsaikosaponin a and 3"-O-acetylsaikosaponin a. The first two compounds are new derivatives of saikosaponin and this is the first isolation of prosaikogenin G from a plant. Their complete 1H and 13C NMR assignments were made by using a combination of 2D NMR techniques (DQF-COSY, HOHAHA, ROESY, HETCOR, HMQC and HMBC). Some of the compounds showed cytotoxic activity against the P-388 cell line.

3-hydroxycoumarin glycosides from Alyxia reinwardti var. Lucida.

Investigation of the inner bark of Alyxia reinwardti var. lucida led to the isolation of two new coumarin glycosides, 1 and 2, whose structures were determined by interpretation of their spectroscopic data, particularly NMR spectroscopy.

Triterpene saponins from Aster yunnanensis.

Four new triterpene saponins, asteryunnanosides A, B, C and D, have been isolated from Aster yunnanensis and their structures deduced as 2 alpha,3 beta,23-trihydroxyolean-12-en-28-oic acid-28-O-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-glucopyranoside, 2 alpha,3 beta,23-trihydroxyolean-12-en-28-oic acid-28-O-beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranoside, 2 alpha,3 beta-dihydroxyolean-12-en-28-oic acid-28-O-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-glucopyranoside and 2 alpha,3 beta-dihydroxyolean-12-en-28-oic acid-28-O-beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranoside, respectively, by means of spectral and chemical data.

Triterpenoid saponins from Aster batangensis.

Four novel triterpenoid saponins named asterbatanoside F, G, H and I were isolated from the roots of Aster batangensis and their structures elucidated as 3-O-beta-D-glucopyranosyl-23-O-acetyl-bayogenin-28-O-beta-D-glu cop yranosyl- (1-->6)-[alpha-L-rhamnopyranosyl-(1-->2)]-beta-D-glucopyranoside, 3-O-beta-D-glucopyranosyl-bayogenin-28-O-beta-D-glucopyranosyl-(1- ->6)-[alpha-f1p4amnopyranosyl-(1-->2)]-beta-D-glucopyranoside, 3-O-beta-D-glucopyranosyl- (1-->3)-beta-D-glucopyranosyl-bayogenin-28-O-beta-D-glucopyranosyl -(1-->6)-beta-D-glucopyranoside, and 3-O-beta-D-glucopyranosyl-(1-->3)-beta-D- glucopyranosyl-23-O-acetyl-bayogenin-28-O-beta-D-glucopyranosyl-(1 -->6)-beta-D- glucopyranoside by means of spectral data, especially NMR including COSY, HETCOR, COLOC, HOHAHA, ROESY and selective INEPT techniques, and chemical evidence.

Further polyoxypregnanes from Marsdenia tenacissima.

Two new polyoxypregnanes, designated marstenacigenins A and B, along with a known compound, dresgenin, were isolated from the mild acid hydrolysate of the ethanol extract of the stems of Marsdenia tenacissima. Their structures were deduced by a combination of 1D and 2D NMR spectroscopic techniques as 12 beta-cinnamoyl-dihydrosarcostin and 12 beta,20-dibenzoyldihydrosarcostin, respectively.

An echinocystic acid saponin derivative from Kalimeris shimadae.

A new triterpene saponin, shimadoside A, has been isolated from Kalimeris shimadae and its structure deduced as 3-O-beta-D-glucopyranosiduronic acid-3 beta, 16 alpha-dihydroxyolean-12-en-28-oic acid-28-O-beta-D-xylopyranosyl-(1-->3)-beta-D-xylopyranosyl-(1--> 4)-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-xylopyranoside by means of spectral data, especially NMR, including COSY, HMQC, HOHAHA and ROESY techniques, and chemical degradation.

Four diterpene esters from Euphorbia myrsinites.

The Turkish species Euphorbia myrsinites has yielded four new tetracyclic diterpene tetraesters from a cytotoxic acetone extract, in addition to the known cycloartane-type triterpenoids and betulin. The new compounds and their hydrolysis product have been extensively characterized by high field spectroscopic techniques, and were shown to be four new tetraesters of the parent alcohol, myrsinol.

Medicagenic acid saponins from Aster batangensis.

Two new medicagenic acid saponins, named asterbatanoside J and K, were isolated from the roots of Aster batangensis. On the basis of chemical and spectral studies especially 2D NMR including COSY, HETCOR, HMQC, HOHAHA, TOCSY, ROESY and HMBC techniques, their structures were established as 3-O-beta-D-glucopyranosyl-(1--> 6)-beta-D-glucopyranosyl-2 beta, 3 beta-dihydroxy-olean-12-en-23 alpha, 28-dioic acid- 28-O-alpha-L-arabinopyranosyl-(1-->3)-alpha-L- rhamnopyranosyl-(1-->2)-beta-D-fucopyranoside and 3-O-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl- medicagenic acid-28-O-beta-D-xylopyranosyl-(-->4)-[alpha-L- arabinopyranosyl-(1 -->3)-alpha-L-rhamnopyranosyl-(1-->2) -beta-D-fucopyranside, respectively.

Aleppicatines A and B from Euphorbia aleppica.

Two new pentacyclic diterpene polyesters, aleppicatine A and B, have been isolated from the acetone extract of the whole plant of Euphorbia aleppica, in addition to five known cycloartane-type triterpenes (24-methylenecycloartanol, cyclolaudenol cycloart-25-en-3 beta-ol-24-one, cycloart-22-en-3 beta,25-diol and cycloart-25-en-3 beta,24-diol), scopoletin, kaempferol and 4-hydroxybenzoic acid and its methyl ether. The structures of the new compounds and their hydrolysis products have been extensively characterized by high-field NMR spectroscopic methods, including 2D NMR techniques.

Glycosides from Aster yunnanensis.

A new oleanane-type triterpene saponin named asteryunnanoside E and a new acetylene glycoside named asteryunnanoside I have been isolated from the roots of Aster yunnanensis, and their structures elucidated as 3-O-beta-D-glucopyranosyl-bayogenin-28-O-beta-D- glucopyranosyl-(1-->2)-beta-D-glucopyranoside and 2Z,8E-decadiene-4,6-diyn-1-O-beta-D-glucopyranos yl-(1-->2)-beta-D- glucopyranoside by means of 1D and 2D NMR techniques (COSY, HETCOR, COLOC, HOHAHA and ROESY) and chemical transformations.

Cytotoxic clerodane diterpenes from Polyalthia barnesii.

Three cytotoxic clerodane diterpenes were purified from an ethyl acetate-soluble extract of the stem bark of Polyalthia barnesii, namely, 16 alpha-hydroxycleroda-3,13(14)Z-dien-15,16-olide, a known compound, and two novel compounds, 3 beta, 16 alpha-dihydroxycleroda-4(18),13(14)Z-dien-15,16-olide and 4 beta, 16 alpha-dihydroxyclerod-13(14)Z-en-15,16-olide. These compounds were found to exhibit broad cytotoxicity against a panel of human cancer cell lines.

Alkyl phenols and derivatives from Tapirira obtusa.

From the bark of Tapiria obtusa, six alkyl phenol derivatives were isolated: 1-hydroxy-3-[(Z)-7'-nonadecenyl]-benzene, 1-hydroxy-3-[(Z)-7'-heptadecenyl]-benzene, 1-hydroxy-3-[14'-phenyltetradecyl]-benzene, and 1-hydroxy-3-[16'-phenyltetradecyl]-benzene, and their possible biogenetic precursors, 1-(16'-phenyl-12'Z-hexadecenyl)-4-Z-cyclohexene-(1S*,3S*)-diol and (4S*,6S*)-dihydroxy-6-(14'Z-nonadecenyl)-2-cyclohexenone. The structures of these compounds were elucidated by chemical and spectroscopic analysis, (4S*,6S*)-Dihydroxy-6-(14'Z-nonadecenyl)-2-cyclohexenone showed cytotoxic activity.

Cytotoxic prenylated flavanones from Monotes engleri.

From the leaves of Monotes engleri, five prenylated flavanones were isolated as constituents that displayed cytotoxic activity against several human cancer cell lines. There of these substances are novel, namely, 6-(1,1-dimethylallyl)naringenin, 6-(1,1-dimethylallyl)eriodictyol and 3'-O-methyl-6-(1,1-dimethylallyl)-eriodictyol, with the other two active substances being the known flavanones, 6,8-diprenyleriodictyol and hiravanone. Additionally, two novel, but non-cytotoxic, biogenetically related flavanones were isolated, 6-[(2RS)-hydroxy-3-methyl-3-butenyl]-8-prenyleriodictyol and 5,4'-dihydroxy-4",4"-dimethyl-5"-methyl-5"H-dihydrofurano[2",3": 6,7]flavanone. The structures of the new compounds were determined by spectral analysis 1D- and 2D-NMR experiments.

A cytotoxic diterpene from Alomia myriadenia.

An extract of the aerial parts from Alomia myriadenia Schultz-Bip. ex Baker (Asteraceae) showed significant cytotoxicity against a panel of human cancer cell lines in a screening of extracts from Brazilian Atlantic Forest plant species. Employing a bioassay-linked HPLC-electrospray/MS method, followed by semi-preparative HPLC, the active component was isolated and characterized as a mixture of epimers of the labdane diterpene 12S,16-dihydroxy-ent-labda-7,13-dien-15,16-olide.

Anacardoside from the seeds of Semecarpus anacardium.

From the seeds of Semecarpus anacardium, a new phenolic glucoside, anacardoside, was isolated, and its structure and configuration were elucidated by a combination of NMR techniques as 1-O-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyloxy-3-hydro xy-5-methylbenzene.