Antineoplastic agents. II. Four furostanol glycosides from rhizomes of Dioscorea collettii var. hypoglauca

Atropurosides A-G, new steroidal saponins from Smilacina atropurpurea

Atropurosides A-G (1-7), seven new steroidal saponins, which possess new polyhydroxylated aglycones, were isolated from the rhizomes of Smilacina atropurpurea (Convallariaceae), together with a known saponin, dioscin (8). Their structures were elucidated on the basis of detailed spectroscopic analysis, including 1D and 2D NMR techniques and chemical methods. Antifungal testing of the eight compounds indicated that atropurosides B (2) and F (6) were fungicidal against Candida albicans, Candida glabrata, Cryptococcus neoformans, and Aspergillus fumigatus with minimum fungicidal concentrations (MFCs) < or = 20 microg/ml, while dioscin (8) was selectively active against C. albicans and C. glabrata (MFC < or = 5.0 microg/ml). Furthermore, the antifungal saponins 2, 6, and 8 were evaluated for their in vitro cytotoxicities in a panel of human cancer cell lines (SK-MEL, KB, BT-549, SK-OV-3, and HepG2) and non-cancerous Vero cells. All showed moderate cytotoxicities. It appears that the antifungal activity of these steroidal saponins correlates with their cytotoxicity against mammalian cells.

Facile Conversion of Spirostan Saponin into Furostan Saponin: Synthesis of Methyl Protodioscin and Its 26-Thio-analogue

[reaction: see text] A facile approach for the conversion of a spirostan saponin into its furostan counterpart, as illustrated by the transformation of dioscin to methyl protodioscin (and its 26-thio-analogue), has been developed.

A new steroidal saponin from Dioscorea cayenensis

The new 26-O-beta-D-glucopyranosyl-3beta,26-dihydroxy-20,22-seco-25(R)-furost-5-en-20,22-dione-3-O-alpha-L-rhamnopyranosyl-(1-->4)-alpha-L-rhamnopyranosyl-(1-->4)-[alpha-L-rhamnopyranosyl-(1-->2)]-beta-D-glucopyranoside (1), along with the known methyl protodioscin (2), asperoside (3) and prosapogenin A of dioscin (4) were isolated from the rhizomes of Dioscorea cayenensis LAM.-HOLL (Dioscoreaceae). Their structures were established mainly on the basis of 600 MHz 2D-NMR spectral data. 4 exhibited antifungal activity against the human pathogenic yeasts Candida albicans, C. glabrata and C. tropicalis (MICs of 20.8, 6.25, 25 microg/ml, respectively), whereas saponins 1-3 were inactive.

Facile synthesis of saponins containing 2,3-branched oligosaccharides by using partially protected glycosyl donors

Two natural saponins 1 and 2, isolated from Solanum indicum L., and containing 2,3-branched sugar moieties, have been efficiently synthesized. Partially protected monosaccharide and disaccharide donors were used to facilitate target synthesis. Stereo factors were critical in incorporating 2,3-branched sugars on steroid aglycones. Saponin 1 was synthesized in five steps and 30% overall yield, while saponin 2 was obtained using six straightforward sequential reactions in 31% overall yield. Saponin 2 shows promising cytotoxic activity toward human hepatocellular carcinoma BEL-7402 with an IC50 of <6 microg/mL.

Synthesis of bidesmosidic dihydrodiosgenin saponins bearing a 3-O-β-chacotriosyl moiety

3-O-beta-Chacotriosyl-26-O-beta-D-glucopyranosyl-(25R)-furost-5-en (1), a mimic of the antitumor active proto-dioscin, was concisely synthesized from diosgenin in a linear nine steps and in 17% overall yield. Its congeners with a alpha-l-rhamnopyranosyl, beta-lactosyl, or without a substituent at the 26-OH (13-15) were also prepared. Compound 1, as well as 13-15, did not show any inhibition against tumor cells, implying that proto-dioscin might be also inactive, but readily converted into the antitumor active dioscin.

Two new pregnane glycosides from Dioscorea futschauensis R. KUNTH

Two new pregnane glycosides (1, 2) together with two known saponins were isolated from the rhizomes of Dioscorea futschauensis R. KUNTH. The structures of 1 and 2 were established as 16alpha-methoxyl-3beta-[(O-alpha-L-rhamnopyranosyl-(1-->2)-O-[alpha-L-rhamnopyranosyl-(1-->4)]-beta-D-glucopyranosyl)oxy]pregn-5-en-20-one and 21-methoxyl-3beta-[(O-alpha-L-rhamnopyranosyl-(1-->2)-O-[alpha-L-rhamnopyranosyl-(1-->4)]-beta-D-glucopyranosyl)oxy]pregn-5,16-en-20-one, respectively, on the basis of two-dimension NMR (2D NMR) and other spectral analysis. Their in vitro bioactivity against plant pathogenic fungus Pyricularia oryzae and osteoblastic proliferation stimulatory activity in the UMR106 cell line were evaluated.

Furostanol saponins from Tribulus terrestris

An HPLC-ELSD-ESI-MS method has been developed for the analysis of the steroidal saponins in the aerial parts of Tribulus terrestris. Protodioscin, a new saponin (5,6-dihydroprotodioscin, neoprotodioscin) and their respective sulfates were detected. The structure of the new compound was elucidated on the basis of NMR and ESI-MS spectral analysis.

The cytotoxicity of methyl protodioscin against human cancer cell lines in vitro

Methyl protodioscin (NSC-698790) was a furostanol saponin isolated from the rhizome of Dioscorea collettii var. hypoglauca (Dioscoreaceae), a Chinese herbal remedy for the treatment of cervical carcinoma, carcinoma of the urinary bladder, and renal tumors for centuries. To systematically evaluate its potential anticancer activity, methyl protodioscin was tested cytotoxicity in vitro against human cancer cell lines by the NCI's (National Cancer Institute) anticancer drug screen. As a result, methyl protodioscin showed strong cytotoxicity against most cell lines from solid tumors with GI50 < or = 10.0 microM, especially selectively against one colon cancer line (HCT-15) and one breast cancer line (MDA-MB-435) with GI50 < 2.0 microM but moderate cytotoxicity was shown against leukemia cell lines with GI50 10-30 microM. The data are consistent with the fact that the rhizome of D. collettii var. hypoglauca has been employed for the treatment of solid tumors rather than leukemia in China for centuries. Based on an analysis using the COMPARE computer program with methyl protodioscin as a seed compound, no compounds in the NCI's anticancer drug screen database have cytotoxicity patterns similar to those of methyl protodioscin, indicating a potential novel mechanism of anticancer action.

The cytotoxicity of methyl protoneogracillin (NSC-698793) and gracillin (NSC-698787), two steroidal saponins from the rhizomes of Dioscorea collettii var. hypoglauca, against human cancer cells in vitro

In our continuous studies of anticancer activity of steroidal saponins from the rhizomes of Dioscorea collettii var. hypoglauca (Dioscoreaceae), methyl protoneogracillin (NSC-698793) and gracillin (NSC-698787) were tested for cytotoxicity against human cancer cell lines from leukemia and eight solid tumor diseases. As a result, methyl protoneogracillin was cytotoxic against all the test cell lines with GI(50) < 100 micro M, especially selectively against two leukemia lines (CCRF-CEM and RPMT-8226), one colon cancer line (KM12), two central nervous system (CNS) cancer lines (SF-539 and U251), one melanoma line (M14), one renal cancer line (786-0), one prostate cancer line (DU-145), and one breast cancer line (MDA-MB-435), with GI(50) < or = 2.0 micro M. Leukemia, CNS cancer, and prostate cancer were the most sensitive subpanels, while ovarian cancer was the least sensitive subpanels. The preliminary toxicity studies showed that the maximum tolerant dose was 600 mg/kg for methyl protoneogracillin to mice. Gracillin was cytotoxic against most cell lines with GI(50), TGI and LC(50) at micromolar levels, but no activity against EKVX (non-small cell lung cancer), HT29 (colon cancer), OVCAR-5 (ovarian cancer), and SN12C (renal cancer). Based on structure-activity relationship, C-25 R/S con fi guration was critical for leukemia selectivity between methyl protoneogracillin and methyl protogracillin. F-ring was critical to selectivity between furostanol (methyl protoneogracillin and methyl protogracillin) and spirostanol (gracillin) saponins in this study. By an analysis of COMPARE software, no compounds in the NCI's database had similar mean graphs to those of methyl protoneogracillin and gracillin, respectively, indicating potential novel mechanism(s) of action involved. Put all in together, methyl protoneogracillin has been selected as a potential anticancer candidate for hollow fi ber assay to nude mice, but gracillin will not be pursued due to lack of selectivity against human cancer diseases.

A new ergostanol saponin from Dioscorea deltoidea Wall var. orbiculata

From the fresh rhizomes of Dioscorea deltoidea Wall var. orbiculata, a novel ergostanol saponin, orbiculatoside A (1), was isolated and identified as 3-O-beta-D-glucopyranosyl-ergost-5-ene-3beta, 26-diol-26-O-beta-D-glucopyranosyl(1-->3)-[beta-D-glucopyranosyl(1-->2)-beta-D-glucupyranosyl(1-->6)]-beta-D-glucopyranoside by various NMR techniques in combination with chemical methods. The new saponin showed strong activity against Pyricularia oryzae, with a MMDC (minimum morphological deformation concentration) value of 28.04 micromol/l and was cytotoxic to cancer cell line K562, HCT-15, A549, HT1080, and A2780a in vitro.

The cytotoxicity of protoneodioscin (NSC-698789), a furostanol saponin from the rhizomes of Dioscorea collettii var. hypoglauca, against human cancer cells in vitro

Protoneodioscin (NSC-698789) is a furostanol saponin isolated from the rhizomes of Dioscorea collettii var. hypoglauca (Dioscoreaceae), a Chinese herbal remedy for cancer treatment. Our studies showed that protoneodioscin is cytotoxic against most cell lines from leukemia and solid tumors in the NCI's (National Cancer Institute, USA) anticancer drug screen. Leukemia, CNS cancer, and prostate cancer are the most sensitive subpanels to protoneodioscin, while melanoma, ovarian cancer, and renal cancer are less sensitive. The preliminary animal studies showed that the maximum tolerant dose of protoneodioscin was 600 mg/kg to mice. Based on an analysis of the COMPARE software with protoneodioscin as a seed compound, no compounds in the NCI's database have similar cytotoxicity patterns to those of protoneodioscin, indicating a potentially novel mechanism of anticancer action involved.

Methyl protogracillin (NSC-698792): the spectrum of cytotoxicity against 60 human cancer cell lines in the National Cancer Institute's anticancer drug screen panel

Methyl protogracillin (NSC-698792) was a furostanol saponin isolated from the rhizome of Dioscorea collettii var. hypoglauca (Dioscoreaceae), a Chinese herbal remedy for the treatment of cervical carcinoma, carcinoma of urinary bladder and renal tumor for centuries, in our previous studies. In order to systematically evaluate its potential anticancer activity, methyl protogracillin was tested for its cytotoxicity in vitro against 60 human cancer cell lines in the National Cancer Institute (NCI)'s anticancer drug screen. As a result, it was found that methyl protogracillin was cytotoxic against all the tested cell lines from leukemia and solid tumors in the NCI's human cancer panel; it showed particular selectivity against one colon cancer line (KM12), one central nervous system (CNS) cancer line (U251), two melanoma lines (MALME-3M and M14), two renal cancer lines (786-0 and UO-31) and one breast cancer line (MDA-MB-231) with GI50< or =2.0 microM. The selectivity between these seven most sensitive lines and the least sensitive line (CCRF-CEM) ranged from 26- to 56-fold. In the same cancer subpanel, selectivity more than 15-fold was observed between MDA-MB-231 and MCF-7, NCI-ADR-RES, BT-549 in breast cancer. From a general view of the mean graph, CNS cancer is the most sensitive subpanel, while ovarian cancer and renal cancer are the least sensitive subpanels. Based on an analysis of the COMPARE computer program with methyl protogracillin as a seed compound, no compounds in the NCI's anticancer drug screen database have similar cytotoxicity patterns (mean graph) to that of methyl protogracillin, indicating a potential novel mechanism of the anticancer action involved.