RESUMEN

Bioactive fractionation, based on multi-drug resistance (MDR) pump inhibition in Staphylococcus aureus, resulted in the isolation of the active inhibitors 5'-methoxyhydnocarpin-D from leaves of Berberis (formerly Mahonia) trifoliolata and pheophorbide a from Berberis fendleri. The hydnocarpin derivative was not found in the latter species. Pheophytin a (the phytol derivative of pheophorbide a) was identified from both species, but it proved to have no MDR pump inhibitory activity. The somewhat uncommon, and inactive, flavonoid tricin was identified from B. trifoliolata. The occurrence of a flavonolignan in Mahonia-tpe species and its absence in Berberis sensu strictu may provide a chemical differentiation between the two groups which are now recombined on the basis of DNA studies. The strong bacterial efflux pump inhibition of pheophorbide a could be of importance as a plant defense against natural pathogens.

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Although some progress has been reported on structure-activity relationships (SARs) for inhibitors of mammalian P-glycoprotein MDR efflux pumps, there is almost nothing in the literature regarding SARs for inhibitors of any bacterial efflux pump. Indeed, only a few of these have been described. Our discovery of a potent naturally occurring flavonolignan inhibitor of the NorA MDR pump of Staphylococcus aureus provided a structural foundation upon which SARs could be assessed via synthetic analogues. Several flavonolignans were prepared which proved to have greater potency than the natural isolate, 5'-methoxyhydnocarpin-D, while others showed decreased potency. Surprisingly, some simple alkylated flavones also were quite active MDR pump inhibitors. Variability of activity among the compounds tested was sufficient so that at least some SARs could be postulated and compared with those known for P-glycoprotein.

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The reported isolation of cis-epoxyconiferyl alcohol must be incorrect, based upon comparison of the reported Nuclear Magnetic Resonance (NMR) spectral data for the isolate with those for synthesized coniferyl and cinnamyl alcohol epoxide derivatives. Attempts to prepare cis- and trans-coniferyl alcohols were unsuccessful, although their acetate derivatives could be synthesized. The NMR spectral data for a synthetic sample of pinoresinol were in excellent agreement with those for the purported isolate.

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Flavonolignans represent natural compounds whose biosynthesis presumes a radical coupling of a ring B catecholic flavonoid with a molecule of coniferyl alcohol or an analogue. Many natural flavonolignans can exist as regioisomers, depending on how the coupled coniferyl alcohol moiety orients to the flavonoid. These regioisomers are often difficult to separate and have virtually identical NMR spectra. Structural assignments for some have changed with time or have been given without proof. We here report syntheses of both regioisomers of the flavonolignan hydnocarpin and one isomer of a plant isolate previously known as 5'-methoxyhydnocarpin. This isomer, here renamed 5'-methoxyhydnocarpin-D, was recently shown to be a potent inhibitor of a Staphylococcus aureus multidrug resistant efflux pump.

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A new method of bioactivity-directed fractionation, based on multidrug resistant pump (MDR) inhibition in Staphylococcus aureus, was demonstrated. This resulted in the isolation, from berberine-containing Berberis species, of two compounds that are themselves devoid of S. aureus antibacterial activity, but that form potent synergistic couples with a subinhibitory concentration of berberine. The bacterial MDR pump inhibitors were identified as the flavonolignan 2 and the porphyrin 3. Another natural flavonolignan, silybin (8) from Silybum marianum, was also shown to be a bacterial MDR pump inhibitor.

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Multidrug resistance pumps (MDRs) protect microbial cells from both synthetic and natural antimicrobials. Amphipathic cations are preferred substrates of MDRs. Berberine alkaloids, which are cationic antimicrobials produced by a variety of plants, are readily extruded by MDRs. Several Berberis medicinal plants producing berberine were found also to synthesize an inhibitor of the NorA MDR pump of a human pathogen Staphylococcus aureus. The inhibitor was identified as 5'-methoxyhydnocarpin (5'-MHC), previously reported as a minor component of chaulmoogra oil, a traditional therapy for leprosy. 5'-MHC is an amphipathic weak acid and is distinctly different from the cationic substrates of NorA. 5'-MHC had no antimicrobial activity alone but strongly potentiated the action of berberine and other NorA substrates against S. aureus. MDR-dependent efflux of ethidium bromide and berberine from S. aureus cells was completely inhibited by 5'-MHC. The level of accumulation of berberine in the cells was increased strongly in the presence of 5'-MHC, indicating that this plant compound effectively disabled the bacterial resistance mechanism against the berberine antimicrobial.

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The toxicity and bioactivity of pyrrolizidine alkaloids (PAs), common constituents of hundreds of plant species, and in herbal remedies and folk medicines prepared thereof, are probably due to their ability to form DNA cross-linking. We investigated DNA cross-linking activity by chemically-activated PAs from four different structural classes in Madin-Darby bovine kidney (MDBK) cells and in pBR322 DNA. In cell culture, alpha,beta-unsaturated macrocyclic diester pyrroles dehydrosenecionine (DHSN), dehydroriddelliine (DHRD) and the saturated macrocyclic diester pyrrole dehydromonocrotaline (DHMO) were significantly more potent cross-linkers than the simple necine base (retronecine) and an N-oxide (indicine N-oxide; INO) as determined by alkaline elution. The proportion of total DNA cross-links that were proteinase K-resistant (DNA-DNA cross-links) induced by the various pyrroles ranged from 0.08 (DHRN) to 0.67 (DHSN). Those pyrroles that were potent cross-linkers of cellular DNA also cross-linked, in a dose-dependent manner, Bam HI-digested pBR322 DNA as assessed by a gel retardation assay. The possible functional relevance of pyrrole-DNA cross-links was determined by their ability to interrupt PCR amplification of a 1.129 kb segment of pBR322. Dehydrosenecionine completely inhibited amplification, while DHMO was of intermediate potency, while DHRN and INO had no effect. Taken together, these studies suggest that structural features, most notably the presence of a macrocyclic diester, confer potent cross-link activity to PAs. In any event, DNA-DNA cross-linking is probably biologically relevant as indicated by their interference with DNA replication.

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A new amide of threo-gamma-hydroxyglutamic acid, justiciamide, was isolated from Justicia ghiesbreghtiana and shown to be (-)-N-(2-hydroxy-4,5-dimethoxyphenyl)-(2 S,4 S)-gamma-hydroxyglutamic acid. Justiciamide is the first amide of an uncommon amino acid found in this genus.

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Three trace alkaloids from Colorado blue spruce, Picea pungens, were identified by synthesis and GC-MS comparisons as 4alpha-hydroxy-cis-2-methyl-6-(2-oxopropyl)piperidine (1), 4alpha-hydroxy-cis-2-methyl-6-propylpiperidine (11), and 1-methylgranatanone (15) (N-methyl-9-aza-1-methylbicyclo[3.3. 1]nonane or N-methyleuphococcinine). Alkaloids 1 and 11 are the first among numerous known pine and spruce piperidines to contain a ring-oxygenated substituent.

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Pyrrolizidine alkaloids (PAs) are toxic constituents of hundreds of plant species, some of which people are exposed to in herbal products and traditional remedies. The bioactivity of PAs are related, at least in part, to their ability to form DNA-protein complexes (DPC). Previous studies from our laboratory indicated a possible role for actin in PA-induced DPCs. Nuclei prepared from Madin-Darby bovine kidney (MDBK) and human breast carcinoma (MCF-7) cells were treated with the pyrrolic PAs dehydrosenecionine (DHSN) and dehydromonocrotaline (DHMO). DPCs were purified and then analyzed by Western immunoblotting. Actin was found in DPCs induced by both DHSN and DHMO, but not in those from control nuclei. Actin was also present in DPCs induced by cisplatinum and mitomycin C, two bifunctional cross-linkers. In separate experiments, DHSN and DHMO were crosslinked to a mixture of HindIII digested lambda phage with varying amounts of glutathione (GSH), cysteine, or methionine to identify the stoichiometry of competition between DNA and alternate nucleophiles for crosslink formation with pyrroles. GSH and cysteine, but not methionine, competed with lambda phage for DNA crosslinking, indicating that reduced thiols may have a role in nucleophilic reactions with pyrroles in the cell. While actin involvement in cisplatinum-induced DPCs is documented, the discovery of actin crosslinking in PA or mitomycin C-treated cells or nuclei is, to our knowledge, novel. Pyrrole-induced DPC formation with actin, a protein with structural and/or regulatory importance proteins, may be a significant mechanism for PA toxicity and bioactivity.

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Isolation and characterization of the new iridoid 10-hydroxy-(5 alpha H)-6-epidihydrocornin from Penstemon secundiflorus (Scrophulariaceae) is described. In biosynthetic experiments, deoxyloganic acid was incorporated into the trans-fused iridoid glycosides (5 alpha H)-6-epidihydrocornin and 10-hydroxy-(5 alpha H)-6-epidihydrocornin in P. secundiflorus. Formation of the trans-fused compounds is therefore a late event in the biosynthesis and does not occur during iridoid formation by cyclization of the open chain monoterpene precursor. In the same plant, 8-epideoxyloganic acid was not incorporated into the trans-iridoids. Deoxyloganic acid was also incorporated into 10-hydroxyhastatoside (which bears an 8 beta-methyl group), while 8-epideoxyloganic acid was incorporated into penstemoside (with an 8 alpha-methyl group). Thus, iridoid biosynthetic pathways leading from both deoxyloganic acid and 8-epideoxyloganic acid were found in the same plant.

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A polar extract of leaves of Justicia ghiesbreghtiana yielded N-(2-hydroxy-4,5-dimethoxyphenyl)-(S)-alpha-malamic acid, 1. Incomplete spectral analysis yielded a hypothetical structure, which was then proven by total synthesis. Coupling of the trifluoroacetate of malic anhydride (trifluoroacetoxysuccinic anhydride) with an arylamine provided the key to regiospecific preparation of the alpha- rather than beta-malamic acids.

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A new alkaloid, isothalisopavine, was isolated from Thalictrum minus and shown to be 2,3,8-trimethoxy-7-hydroxyisopavine from spectral evidence. The known thalisopavine, from T. dasycarpum, is 2,3,8-trimethoxy-9-hydroxyisopavine. Isothalisopavine is the first of its class to be substituted unsymmetrically in the two aromatic rings.

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Two new trans-fused iridoid glycosides (5 alpha H)-6 alpha-8-epidihydrocornin and (5 alpha H)-6 alpha-8-hydroxy-8-epiloganin, were isolated from Penstemon mucronatus, along with cornin, penstemoside and three hastatosides. The trans-fused iridoids are only the second and third known among over 900 described cis-fused iridoid glycosides. Two pairs of iridoids, identical except for the stereochemistry at C-8, were found. Structures were determined by spectroscopic methods.

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Further investigation of the ether extract of the aerial parts of Fagonia glutinosa utilizing the brine shrimp bioassay resulted in the isolation of two new cytotoxic erythroxan diterpenes: 1 alpha, 10 alpha-epoxy-2-oxofagonene (1) and 1 beta, 10 beta-epoxy-2-oxofagonene (2). In addition, two inactive diterpenes, 2-oxofagonene (3) and its previously reported isomer 2-oxo-5-epi-fagonene (4), were also isolated.

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The novel iridoid glycosides, isounedoside and grandifloric acid, were isolated from Thunbergia grandiflora. Grandifloric acid contains C-10 as a carboxylic acid group, the presence of which was predicted by recent iridoid biosynthesis studies carried out within T. alata. Isounedoside contains a rare 6,7-epoxide functional group. A revision in some of the NMR spectral assignments for the known iridoid glycoside alatoside was also made.

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Herbal medications and other nontraditional medical therapies are becoming increasingly popular in the United States. We describe three children and three adults in whom severe toxic effects developed after ingestion of a Chinese herbal medication, jin bu huan, which is sold as Jin Bu Huan Anodyne Tablets. Jin bu huan produced distinct clinical syndromes after acute ingestion in children and long-term use in adults. A single, acute ingestion in children rapidly produced life-threatening neurologic and cardiovascular manifestations, while long-term jin bu huan use in adults was associated with hepatitis. Jin bu huan contains levo-tetrahydropalmatine, a potent neuroactive substance. The constituents of jin bu huan are misidentified on the package, resulting in significant delay in identifying the plant alkaloid responsible for its toxicity. Although perceived as innocuous, jin bu huan may produce major health effects. The highly concentrated formulation, the lack of childproof packaging, and the product insert listing indications for the treatment of serious medical conditions may all contribute to the development of toxic reactions.

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New pyridine monoterpene alkaloids (PMTAs) have been synthesized from the iridoid glycosides 8-epi-loganin, cornin, and antirrinoside by treatment with beta-glucosidase and aqueous NH4-OAc. The PMTA from antirrinoside contained an 8-alpha-OAc group from the opened 7,8-epoxide moiety. Treatment of genipin, the aglycone of geniposide, with HCl(g) and NH3(g) yielded the PMTA racemigerine, a known plant isolate, in which the C=C-CH2OH side chain was converted to C=C-CH3. Reaction of geniposide with beta-glucosidase and aqueous NH4OAc led to oligomeric alkaloids, but at high dilution a dimer was obtained whose structure was formally that of a Diels-Alder adduct between racemigerine and a dihydropyridine. These biomimetic semisyntheses were analyzed in terms of reaction mechanisms and the relative paucity of known plant PMTAs in comparison with the multitudinous occurrence of their presumed iridoid glycoside precursors.

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Roots of Salvia lanigera Poir. yielded a new icetexane [10,12-dihydroxy-9(10-->20)-abeo-8,11,13-abietatriene], named lanigerol, which had activity (MIC 1 mg/ml) against Gram-positive bacteria.

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