Protoneogracillin

Characterization of the cholesterol biosynthetic pathway in Dioscorea transversa.[Pubmed:37142228]

J Biol Chem. 2023 Jun;299(6):104768.

Cholesterol is the precursor of bioactive plant metabolites such as steroidal saponins. An Australian plant, Dioscorea transversa, produces only two steroidal saponins: 1beta-hydroxyProtoneogracillin and Protoneogracillin. Here, we used D. transversa as a model in which to elucidate the biosynthetic pathway to cholesterol, a precursor to these compounds. Preliminary transcriptomes of D. transversa rhizome and leaves were constructed, annotated, and analyzed. We identified a novel sterol side-chain reductase as a key initiator of cholesterol biosynthesis in this plant. By complementation in yeast, we determine that this sterol side-chain reductase reduces Delta(24,28) double bonds required for phytosterol biogenesis as well as Delta(24,25) double bonds. The latter function is believed to initiate cholesterogenesis by reducing cycloartenol to cycloartanol. Through heterologous expression, purification, and enzymatic reconstitution, we also demonstrate that the D. transversa sterol demethylase (CYP51) effectively demethylates obtusifoliol, an intermediate of phytosterol biosynthesis and 4-desmethyl-24,25-dihydrolanosterol, a postulated downstream intermediate of cholesterol biosynthesis. In summary, we investigated specific steps of the cholesterol biosynthetic pathway, providing further insight into the downstream production of bioactive steroidal saponin metabolites.

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.[Pubmed:12820229]

Phytother Res. 2003 Jun;17(6):620-6.

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.

Antineoplastic agents. II. Four furostanol glycosides from rhizomes of Dioscorea collettii var. hypoglauca.[Pubmed:17252340]

Planta Med. 1997 Apr;63(2):161-5.

During activity-guided fractionations to screen for antineoplastic agents, further studies by means of preparative HPLC led to the isolation of four known furostanol saponins: protoneodioscin, protodioscin, Protoneogracillin, protogracillin, along with their corresponding artifacts: methyl protoneodioscin, methyl protodioscin, methyl Protoneogracillin, and methyl protogracillin, from the rhizomes of Dioscorea collettii var. hypoglauca. Among them, protoneodioscin, protodioscin, and Protoneogracillin are first reported from the title plant. The structures of the compounds were established on the basis of chemical evidence and spectral analysis (1H-NMR, 13C-IMMR, 1H-1H COSY, HMQC, HMBC, and FAB-MS). These eight compounds all caused morphological abnormality of Pyricularia oryzae mycelia. They also showed cytotoxic activities against the cancer cell line of K562 in vitro as antineoplastic agents.