Isolation and structural determination of steroidal glycosides from the bulbs of easter lily (Lilium longiflorum Thunb.).

The bulbs of the Easter lily ( Lilium longiflorum Thunb.) are used as a food and medicine in several Asian cultures, and they are cultivated as an ornamental plant throughout the world. A new steroidal glycoalkaloid and two new furostanol saponins, along with two known steroidal glycosides, were isolated from the bulbs of L. longiflorum. The new steroidal glycoalkaloid was identified as (22R,25R)-spirosol-5-en-3beta-yl O-alpha-l-rhamnopyranosyl-(1-->2)-[6-O-acetyl-beta-d-glucopyranosyl-(1-->4)]-beta-d-glucopyranoside. The new furostanol saponins were identified as (25R)-26-O-(beta-d-glucopyranosyl)-furost-5-en-3beta,22alpha,26-triol 3-O-alpha-l-rhamnopyranosyl-(1-->2)-alpha-l-arabinopyranosyl-(1-->3)-beta-d-glucopyranoside and (25R)-26-O-(beta-d-glucopyranosyl)-furost-5-en-3beta,22alpha,26-triol 3-O-alpha-l-rhamnopyranosyl-(1-->2)-alpha-l-xylopyranosyl-(1-->3)-beta-d-glucopyranoside. The previously known steroidal glycosides, (22R,25R)-spirosol-5-en-3beta-yl O-alpha-l-rhamnopyranosyl-(1-->2)-beta-d-glucopyranosyl-(1-->4)-beta-d-glucopyranoside and (25R)-26-O-(beta-d-glucopyranosyl)-furost-5-en-3beta,22alpha,26-triol 3-O-alpha-l-rhamnopyranosyl-(1-->2)-beta-d-glucopyranosyl-(1-->4)-beta-d-glucopyranoside were identified in L. longiflorum for the first time. These new compounds from L. longiflorum and the isolation methodologies employed can be used for studies on the biological role of steroidal glycosides in plant development and plant-pathogen interactions, as well as for studies in food and human health, for which little is known.

Probing a putative dantrolene-binding site on the cardiac ryanodine receptor.

Dantrolene is an inhibitor of intracellular Ca2+ release from skeletal muscle SR (sarcoplasmic reticulum). Direct photoaffinity labelling experiments using [3H]azidodantrolene and synthetic domain peptides have demonstrated that this drug targets amino acids 590-609 [termed DP1 (domain peptide 1)] of RyR1 (ryanodine receptor 1), the skeletal muscle RyR isoform. Although the identical sequence exists in the cardiac isoform, RyR2 (residues 601-620), specific labelling of RyR2 by dantrolene has not been demonstrated, even though some functional studies show protective effects of dantrolene on heart function. Here we test whether dantrolene-active domains exist within RyR2 and if so, whether this domain can be modulated. We show that elongated DP1 sequences from RyR1 (DP1-2s; residues 590-628) and RyR2 (DP1-2c; residues 601-639) can be specifically photolabelled by [3H]azidodantrolene. Monoclonal anti-RyR1 antibody, whose epitope is the DP1 region, can recognize RyR1 but not RyR2 in Western blot and immunoprecipitation assays, yet it recognizes both DP1-2c and DP1-2s. This suggests that although the RyR2 sequence has an intrinsic capacity to bind dantrolene in vitro, this site may be poorly accessible in the native channel protein. To examine whether it is possible to modulate this site, we measured binding of [3H]dantrolene to cardiac SR as a function of free Ca2+. We found that > or =10 mM EGTA increased [3H]dantrolene binding to RyR2 by approximately 2-fold. The data suggest that the dantrolene-binding site on RyR2 is conformationally sensitive. This site may be a potential therapeutic target in cardiovascular diseases sensitive to dysfunctional intracellular Ca2+ release.

Oxidation of indole substrates by oxodiperoxomolybdenum.trialkyl(aryl)-phosphine oxide complexes.

A series of oxodiperoxo molybdenum complexes MoO(5).O=PR(3).L, where R = Me, Et, Pr, Bu, or Ph, have been synthesized. The X-ray crystal structures for the complexes with triethylphosphine oxide and tripropylphosphine oxide as ligands were obtained. These complexes oxidize indoles to various indolone products depending on the substitution pattern of the indole substrate.

Synthesis of the mitomycin and FR900482 ring systems via dimethyldioxirane oxidation.

[reaction: see text] Dimethyldioxirane oxidizes a 2,3-dihydo-1H-pyrrolo[1,2-a]indole unsubstituted at the C-9 position stereoselectively to form a hydroxy ketone with all the basic elements of the mitomycin ring system. On the other hand, a 2,3-dihydo-1H-pyrrolo[1,2-a]indole derivative substituted with an alkyl group at C-9 undergoes an oxidative ring expansion in the presence of dimethyldioxirane to give an FR900482 analogue.

Identification of a dantrolene-binding sequence on the skeletal muscle ryanodine receptor.

Dantrolene is a drug that suppresses intracellular Ca(2+) release from sarcoplasmic reticulum (SR) in skeletal muscle and is used as a therapeutic agent in individuals susceptible to malignant hyperthermia. Although its precise mechanism of action has not been elucidated, we have identified the N-terminal region (amino acids 1-1400) of the skeletal muscle isoform of the ryanodine receptor (RyR1), the primary Ca(2+) release channel in SR, as a molecular target for dantrolene using the photoaffinity analog [(3)H]azidodantrolene. Here, we demonstrate that heterologously expressed RyR1 retains its capacity to be specifically labeled with [(3)H]azidodantrolene, indicating that muscle specific factors are not required for this ligand-receptor interaction. Synthetic domain peptides of RyR1 previously shown to affect RyR1 function in vitro and in vivo were exploited as potential drug binding site mimics and used in photoaffinity labeling experiments. Only DP1 and DP1-2s, peptides containing the amino acid sequence corresponding to RyR1 residues 590-609, were specifically labeled by [(3)H]azidodantrolene. A monoclonal anti-RyR1 antibody that recognizes RyR1 and its 1400-amino acid N-terminal fragment recognizes DP1 and DP1-2s in both Western blots and immunoprecipitation assays and specifically inhibits [(3)H]azidodantrolene photolabeling of RyR1 and its N-terminal fragment in SR. Our results indicate that synthetic domain peptides can mimic a native, ligand-binding conformation in vitro and that the dantrolene-binding site and the epitope for the monoclonal antibody on RyR1 are equivalent and composed of amino acids 590-609.