A Tri-O-Bridged Diels-Alder Adduct from Cortex Mori Radicis.
ABSTRACT: Sanggenon X, an unusual tri-O-bridged Diels-Alder adduct, was isolated from Cortex Mori Radicis. Its structure was established by spectroscopic analysis, including NMR and HR-MS (High Resolution Mass Spectrometry). Sanggenon X contained three O-bridged rings, where the oxygenated bridgeheads were all quaternary carbons. Chemical methylation was carried out to deduce the linkages of the three O-bridges. The absolute configuration was determined by calculating the ECD (Electronic Circular Dichroism) using the TDDFT (Time-Dependent Density Functional Theory) method. Sanggenon X showed significant antioxidant activity against Fe2+-Cys-induced lipid peroxidation in rat liver microsomes, and was as effective as the positive control, curcumin.
Project description:Sanggenons C and D are two Diels-Alder-type adducts from Chinese crude drug Sang-bai-pi. Structurally, both sanggenons construct stereoisomers. In the study, they were comparatively determined using four antioxidant assays, including ferric ion reducing antioxidant power (FRAP) assay, Cu<sup>2+</sup>-reducing assay, 1,1-diphenyl-2-picryl-hydrazl (DPPH•)-scavenging assay, and 2,2'-azino-bis (3-ethylbenzo-thiazoline-6-sulfonic acid radical (ABTS•?)-scavenging assay. Their Fe<sup>2+</sup>-binding reactions were explored using UV-Vis spectra. Finally, their cytoprotective effects were evaluated using flow cytometry. In electron transfer (ET)-based FRAP and Cu<sup>2+</sup>-reducing assays, sanggenon D was found to have lower IC<sub>50</sub> values than sanggenon C; however, in multi-pathway-based DPPH•-scavenging and ABTS•?-scavenging assays, sanggenon C possessed lower IC<sub>50</sub> values than sanggenon D. UV-Vis spectra suggested that sanggenon C generated a bathochromic-shift (286 nm ? 302 nm) and displayed stronger UV absorption than sanggenon D. In flow cytometry, sanggenon C and sanggenon D, respectively, exhibited 31.1% and 42.0% early apoptosis-percentages towards oxidative-stressed mesenchymal stem cells (MSCs). In conclusion, both sanggenons may undergo multiple pathways (e.g., ET and Fe<sup>2+</sup>-binding) to protect MSCs against oxidative stress. In the mere ET aspect, sanggenon D possesses a higher level than sanggenon C, while in multi-pathway-based radical-scavenging, Fe<sup>2+</sup>-binding, and cytoprotection aspects, sanggenon C is more active than sanggenon D. These discrepancies can conclusively be attributed to the steric effect.
Project description:Metal-catalyzed, double Claisen rearrangement of a bis-allyloxyflavone has been utilized to enable a concise synthesis of the hydrobenzofuro[3,2-b]chromenone core structure of the natural products sanggenon A and sanggenol F. In addition, catalytic, enantioselective [4+2] cycloadditions of 2'-hydroxychalcones have been accomplished using B(OPh)3/BINOL complexes. Asymmetric syntheses of the flavonoid Diels-Alder natural products sanggenons C and O have been achieved employing a stereodivergent reaction of a racemic mixture (stereodivergent RRM) involving [4+2] cycloaddition.
Project description:Bis-adducts of 1,2,3,4-tetrahalo-5,5-dimethoxycyclopentadiene and 1,3-butadiene, generated in situ from 3-sulfolene, have been synthesized in excellent yield. Ruthenium catalyzed oxidation of the bis-adducts followed by a one-pot transformation of the resulting alpha-diketone furnished oxa-bridged compounds. Unambiguous stereochemical assignments of both diastereomeric series are reported.
Project description:The Diels-Alder cycloaddition between bisdienes and bisdienophile incorporating the 7-oxa-bicyclo[2.2.1]heptane unit are well known to show high diastereoselectivity that can be exploited for the synthesis of molecular belts. The related bisdiene 5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octene is a valuable building block for the synthesis of photoprecursors for acenes, but it has not been employed for the synthesis of molecular belts. The present work investigates by computational means the Diels-Alder reaction between these bisdiene building blocks with <i>syn</i>-1,4,5,8-tetrahydro-1,4:5,8-diepoxyanthracene, which shows that the diastereoselectivity of the Diels-Alder reaction of the etheno-bridged bisdiene is lower than that of the epoxy-bridged bisdiene. The reaction of the etheno-bridged bisdiene and <i>syn</i>-1,4,5,8-tetrahydro-1,4:5,8-diepoxyanthracene in 2:1 ratio yields two diastereomers that differ in the orientation of the oxa and etheno bridges based on NMR and X-ray crystallography. The all-<i>syn</i> diastereomer can be transformed into a molecular belt by inter- and intramolecular Diels-Alder reactions with a bifunctional building block. The molecular belt could function as a synthetic intermediate <i>en route</i> to a cyclacene photoprecursor.
Project description:Despite their great utility in synthetic and materials chemistry, Diels-Alder (DA) and retro Diels-Alder (rDA) reactions have been vastly unexplored in promoting self-assembly processes. Herein we describe the first example of a retro Diels-Alder (rDA) reaction-triggered self-assembly method. Release of the steric bulkiness associated with the bridged bicyclic DA adduct by the rDA reaction allowed generation of two building blocks that spontaneously self-assembled to form a supramolecular polymer. By employing photopolymerizable lipid building blocks, we demonstrated the efficiency of the rDA-based self-assembly strategy. Generation of reactive functional groups (maleimide and furan) that can be used for further modification of the supramolecular polymer is an additional meritorious feature of the rDA-based approach. Advantage was taken of reactive functional groups to fabricate stimulus-responsive selective and tunable colorimetric sensors. The strategy developed in this study should be useful for the design of systems that participate in triggered molecular assembly.
Project description:Quorum sensing auto-inducers of the <i>N</i>-acyl homoserine lactone (AHL) type produced by Gram-negative bacteria have different effects on plants including stimulation on root growth and/or priming or acquirement of systemic resistance in plants. In this communication the influence of AHL production of the plant growth promoting endophytic rhizosphere bacterium <i>Acidovorax radicis</i> N35 on barley seedlings was investigated. <i>A. radicis</i> N35 produces 3-hydroxy-C10-homoserine lactone (3-OH-C10-HSL) as the major AHL compound. To study the influence of this QS autoinducer on the interaction with barley, the <i>araI</i>-biosynthesis gene was deleted. The comparison of inoculation effects of the <i>A. radicis</i> N35 wild type and the <i>araI</i> mutant resulted in remarkable differences. While the N35 wild type colonized plant roots effectively in microcolonies, the <i>araI</i> mutant occurred at the root surface as single cells. Furthermore, in a mixed inoculum the wild type was much more prevalent in colonization than the <i>araI</i> mutant documenting that the <i>araI</i> mutation affected root colonization. Nevertheless, a significant plant growth promoting effect could be shown after inoculation of barley with the wild type and the <i>araI</i> mutant in soil after 2 months cultivation. While <i>A. radicis</i> N35 wild type showed only a very weak induction of early defense responses in plant RNA expression analysis, the <i>araI</i> mutant caused increased expression of flavonoid biosynthesis genes. This was corroborated by the accumulation of several flavonoid compounds such as saponarin and lutonarin in leaves of root inoculated barley seedlings. Thus, although the exact role of the flavonoids in this plant response is not clear yet, it can be concluded, that the synthesis of AHLs by <i>A. radicis</i> has implications on the perception by the host plant barley and thereby contributes to the establishment and function of the bacteria-plant interaction.
Project description:?,?-Unsaturated acylammonium salts are useful dienophiles enabling highly enantioselective and stereodivergent Diels-Alder-initiated organocascades with furan-based dienes. Complex polycyclic systems can thus be obtained from readily prepared dienes, commodity acid chlorides, and a chiral isothiourea organocatalyst under mild conditions. We describe the use of furan-based dienes bearing pendant sulfonamides leading to the generation of oxa-bridged, trans-fused tricyclic ?-lactams. This process constitutes the first highly enantio- and diastereoselective, organocatalytic Diels-Alder cycloadditions with these typically problematic dienes due to their reversibility. Computational studies suggest that the high diastereoselectivity with these furan dienes may be due to a reversible Diels-Alder cycloaddition for the endo adducts. In addition, the utility of this methodology is demonstrated through a concise approach to a core structure with similarity to the natural product isatisine A and a nonpeptidyl ghrelin-receptor inverse agonist.
Project description:Fusarium oxysporum f.sp. radicis-lycopersici (FORL) is one of the most destructive necrotrophic pathogens affecting tomato crops, causing considerable field and greenhouse yield losses. Despite such major economic impact, little is known about the molecular mechanisms regulating Fusarium oxysporum f.sp. radicis-lycopersici resistance in tomato.A transcriptomic experiment was carried out in order to investigate the main mechanisms of FORL response in resistant and susceptible isogenic tomato lines. Microarray analysis at 15 DPI (days post inoculum) revealed a distinct gene expression pattern between the two genotypes in the inoculated vs non-inoculated conditions. A model of plant response both for compatible and incompatible reactions was proposed. In particular, in the incompatible interaction an activation of defense genes related to secondary metabolite production and tryptophan metabolism was observed. Moreover, maintenance of the cell osmotic potential after the FORL challenging was mediated by a dehydration-induced protein. As for the compatible interaction, activation of an oxidative burst mediated by peroxidases and a cytochrome monooxygenase induced cell degeneration and necrosis.Our work allowed comprehensive understanding of the molecular basis of the tomato-FORL interaction. The result obtained emphasizes a different transcriptional reaction between the resistant and the susceptible genotype to the FORL challenge. Our findings could lead to the improvement in disease control strategies.