Identification of Kukoamine A, Zeaxanthin, and Clexane as New Furin Inhibitors.

The endogenous protease furin is a key protein in many different diseases, such as cancer and infections. For this reason, a wide range of studies has focused on targeting furin from a therapeutic point of view. Our main objective consisted of identifying new compounds that could enlarge the furin inhibitor arsenal; secondarily, we assayed their adjuvant effect in combination with a known furin inhibitor, CMK, which avoids the SARS-CoV-2 S protein cleavage by means of that inhibition. Virtual screening was carried out to identify potential furin inhibitors. The inhibition of physiological and purified recombinant furin by screening selected compounds, Clexane, and these drugs in combination with CMK was assayed in fluorogenic tests by using a specific furin substrate. The effects of the selected inhibitors from virtual screening on cell viability (293T HEK cell line) were assayed by means of flow cytometry. Through virtual screening, Zeaxanthin and Kukoamine A were selected as the main potential furin inhibitors. In fluorogenic assays, these two compounds and Clexane inhibited both physiological and recombinant furin in a dose-dependent way. In addition, these compounds increased physiological furin inhibition by CMK, showing an adjuvant effect. In conclusion, we identified Kukoamine A, Zeaxanthin, and Clexane as new furin inhibitors. In addition, these drugs were able to increase furin inhibition by CMK, so they could also increase its efficiency when avoiding S protein proteolysis, which is essential for SARS-CoV-2 cell infection.

Design and Fabrication of Dual Redox Responsive Nanoparticles with Diselenide Linkage Combined Photodynamically to Effectively Enhance Gene Expression.

BACKGROUND: PEI is currently the most used non-viral gene carrier and the transfection efficiency is closely related to the molecular weight; however, the prominent problem is that the cytotoxicity increased with the molecular weight. METHODS: A novel redox responsive biodegradable diselenide cross-linked polymer (dPSP) was designed to enhance gene expression. ICG-pEGFP-TRAIL/dPSP nanoparticles with high drug loading are prepared, which have redox sensitivity and plasmid protection. The transfection efficiency of dPSP nanoparticle was evaluated in vitro. RESULTS: The plasmid was compressed by 100% at the N/P ratio of 16, and the particle size was less than 100 nm. When explored onto high concentrations of GSH/H2O2, dPSP4 degraded into small molecular weight cationic substances with low cytotoxicity rapidly. Singlet oxygen (1O2) was produced when indocyanine green (ICG) was irradiated by near-infrared laser irradiation (NIR) to promote oxidative degradation of dPSP4 nanoparticles. Under the stimulation of NIR 808 and redox agent, the particle size and PDI of ICG-pDNA/dPSP nanoparticle increased significantly. CONCLUSION: Compared with gene therapy alone, co-transportation of dPSP4 nanoparticle with ICG and pEGFP-TRAIL had better antitumor effect. Diselenide-crosslinked polyspermine had a promising prospect on gene delivery and preparation of multifunctional anti-tumor carrier.

Separation and Characterization of Phenolamines and Flavonoids from Rape Bee Pollen, and Comparison of Their Antioxidant Activities and Protective Effects Against Oxidative Stress.

Phenolamines and flavonoids are two important components in bee pollen. There are many reports on the bioactivity of flavonoids in bee pollen, but few on phenolamines. This study aims to separate and characterize the flavonoids and phenolamines from rape bee pollen, and compare their antioxidant activities and protective effects against oxidative stress. The rape bee pollen was separated to obtain 35% and 50% fractions, which were characterized by HPLC-ESI-QTOF-MS/MS. The results showed that the compounds in 35% fraction were quercetin and kaempferol glycosides, while the compounds in 50% fraction were phenolamines, including di-p-coumaroyl spermidine, p-coumaroyl caffeoyl hydroxyferuloyl spermine, di-p-coumaroyl hydroxyferuloyl spermine, and tri-p-coumaroyl spermidine. The antioxidant activities of phenolamines and flavonoids were evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS), and ferric reducing antioxidant power (FRAP) assays. It was found that the antioxidant activity of phenolamines was significantly higher than that of flavonoids. Moreover, phenolamines showed better protective effects than flavonoids on HepG2 cells injured by AAPH. Furthermore, phenolamines could significantly reduce the reactive oxygen species (ROS), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, and increase the superoxide dismutase (SOD) and glutathione (GSH) levels. This study lays a foundation for the further understanding of phenolamines in rape bee pollen.

Comparative Study of the Chemical Constituents and Bioactivities of the Extracts from Fruits, Leaves and Root Barks of Lycium barbarum.

The fruits, leaves and root barks of L. barbarum plant are widely used as functional foods and as ingredients in traditional Chinese prescriptions and patent medicines. They are considered to have different pharmacological activities and health benefits because of their diverse constituents. Here, the chemical constituents of the extracts from fruits, leaves and root barks of L. barbarum were compared by ultra-high performance liquid chromatography coupled with high resolution mass spectrometry (UPLC-HR-MS). A total of 131 compounds were identified and seven of them were quantified. Among them, 98, 28 and 35 constituents were detected in fruits, leaves and root barks respectively. Dicaffeoylspermidine/spermine derivatives were the most detected compounds (74/131); among them, dicaffeoylspermine isomers and propionyl-dicaffeoylspermidine were found in root barks in very large amounts (e.g., kukoamine B = 10.90 mg/g dry powder); dicaffeoyl-spermidine isomers were detected in fruits/leaves in a high amount, and many of their glycosylated derivatives were mainly detected in fruits. In addition, six saponins from L. barbarum fruits were reported for the first time, and 5,6-dihydrosolasonine was reported for the first time in plants. The activity assays showed that the root bark extract possessed the strongest antioxidative activity and cytotoxicity, which was presumed due to the large amount of dicaffeoylspermine/spermidines in root barks. Fourteen potential bioactive components from fruits were identified by a target cell-based screening method. These results will help to understand the different biological activities of these three parts of L. barbarum plant and will benefit the discovery of new functional components.

Functional preserving carbon dots-based fluorescent probe for mercury (II) ions sensing in herbal medicines via coordination and electron transfer.

Mercury ions (Hg2+) are one of the compulsory items in the quality control of herbal medicines for its serious toxicity to human health. Highly selective and sensitive Hg2+ detection, especially in complex real samples, is still challenging. In this work, Fluorescent (FL) carbon dots (CDs) with a core-shell structures composed of the crystalline core of stacked sp2-hybridized carbon layers and the shell of functional groups on the periphery of carbon layers are facilely prepared through a one-step hydrothermal synthetic route. They can specifically interact with Hg2+ in aqueous medium to form aggregates, during which coordination of carboxyl functional groups on the surface of CDs with Hg2+ occurred, which facilitated electron transfer from the CDs to Hg2+. As a result, fluorescence of the CDs was quenched with a high efficiency, making the detection of Hg2+ highly sensitive with the limit of determination (LOD) of 2.2 nM (3σ). With that, detection of Hg2+ in the complex compound herbal medicines samples with highly reproducible results has been successfully realized by using the as-prepared CDs, showing that fluorescent CDs-based probe may have great potential in the quality controls of heavy metals for pharmaceutical analysis.

Identification and Characterization of Kukoamine Metabolites by Multiple Ion Monitoring Triggered Enhanced Product Ion Scan Method with a Triple-Quadruple Linear Ion Trap Mass Spectrometer.

Kukoamines are a series of bioactive phytochemicals conjugated by a polyamine backbone and phenolic moieties. Understanding the structural diversity of kukoamine metabolites in plants is meaningful for drug discovery. In this study, an LC-MS/MS method was established for kukoamine profiling and characterization from lycii cortex (LyC) via a triple-quadrupole linear ion trap mass spectrometry (Q-TRAP). On the basis of the typical fragmentation of kukoamine, a diagnostic ion, which represents the features of the backbone and phenolic substitute, was chosen as the product ion for precursor ion scan, and then the screened precursor ions were applied to a successive multiple ion monitoring triggered enhanced product ion scan (MIM-EPI) to simultaneously present the profile survey and MS/MS acquisition. Because the MIM narrowed the ion scan range in Q1 and the ion trap enhanced the ion fragments passing through Q2, the qualitative capability of quadrupole MS can be greatly improved, especially for capture of the uncommon metabolites. There are 12 kukoamine metabolites identified from LyC, with either spermine or spermidine backbone and with conjugation of one to three dihydrocaffeoyls or other kinds of phenolic moieties. Except for kukoamines A and B, other metabolites were identified in LyC for the first time. This approach can be utilized for metabolite identification in other substrates.

Ultrahigh-resolution crystal structures of Z-DNA in complex with Mn(2+) and Zn(2+) ions.

X-ray crystal structures of the spermine(4+) form of the Z-DNA duplex with the self-complementary d(CG)3 sequence in complexes with Mn(2+) and Zn(2+) cations have been determined at the ultrahigh resolutions of 0.75 and 0.85 Å, respectively. Stereochemical restraints were only used for the sperminium cation (in both structures) and for nucleotides with dual conformation in the Zn(2+) complex. The Mn(2+) and Zn(2+) cations at the major site, designated M(2+)(1), bind at the N7 position of G6 by direct coordination. The coordination geometry of this site was octahedral, with complete hydration shells. An additional Zn(2+)(2) cation was bis-coordinated in a tetrahedral fashion by the N7 atoms of G10 and G12 from a symmetry-related molecule. The coordination distances of Zn(2+)(1) and Zn(2+)(2) to the O6 atom of the guanine residues were 3.613 (6) and 3.258 (5) Å, respectively. Moreover, a chloride ion was also identified in the coordination sphere of Zn(2+)(2). Alternate conformations were observed in the Z-DNA-Zn(2+) structure not only at internucleotide linkages but also at the terminal C3'-OH group of G12. The conformation of the sperminium chain in the Z-DNA-Mn(2+) complex is similar to the spermine(4+) conformation in analogous Z-DNA-Mg(2+) structures. In the Z-DNA-Zn(2+) complex the sperminium cation is disordered and partially invisible in electron-density maps. In the Z-DNA-Zn(2+) complex the sperminium cation only interacts with the phosphate groups of the Z-DNA molecules, while in the Z-DNA-Mn(2+) structure it forms hydrogen bonds to both the phosphate groups and DNA bases.

Application of a molecularly imprinted polymer for the extraction of kukoamine a from potato peels.

A molecularly imprinted polymer (MIP) for the purification of N(1),N(12)-bis(dihydrocaffeoyl)spermine (kukoamine A) was computationally designed and tested. The properties of the polymer were characterized. The protocol of the solid phase extraction (SPE) of kukoamine A from potato peels was optimized. A HPLC-MS method for the quantification of kukoamine A was developed and used for all optimization studies. The capacity of the MIP in relation to kukoamine A from the potato peels extract was estimated at 54 mg/g of the polymer. The kukoamine A purified from potato extract using MIP was exceptionally pure (≈ 90%). Although the corresponding blank polymer was less selective than the MIP for the extraction of kukoamine A from the potato extract, it was shown that the blank polymer could be effectively used for the purification of the crude synthetic kukoamine (polymer capacity = 80 mg of kukoamine A/g of the adsorbent, kukoamine A purity ≈ 86%). Therefore, selective adsorbents could be computationally designed for other plant products, allowing their purification in quantities that would be sufficient for more detailed studies and potential practical applications.

Photodynamic effects of porphyrin-polyamine conjugates in human breast cancer and keratinocyte cell lines.

Porphyrin-polyamine conjugates bearing two (cis or trans position) or four spermidine or spermine units were synthesized. We studied the photostability, the hydrophilic/lipophilic balance of porphyrin-polyamine derivatives and the production of singlet oxygen. All these compounds possess physicochemical features required for their use in PDT. Then, we investigated the photocytotoxic efficacy of these porphyrin-polyamine derivatives and the cell death pathway implicated. All compounds appear to be more efficient than Photofrin® to induce HaCat and MCF7 cell death, essentially by apoptosis. Collectively, these data show that porphyrin-polyamine conjugates could be promising phototherapeutic agents.

Supramolecular self-assembling cyanine as an alternative to ethidium bromide displacement in DNA-drug model interactions during high throughput screening.

Supramolecular self-assembling cyanine and spermine binding to genomic DNA was a model for DNA-drug interactions during high throughput screening. Spermine competitively inhibited the self-assembly of cyanine upon DNA scaffolds as signaled by decreased fluorescence from the DNA-cyanine J-aggregate. The sequence of DNA exposure to cyanine or spermine was critical in determining the magnitude of inhibition. Methanol potentiated spermine inhibition by >10-fold. The IC(50) and association constant (K(a)) in 16% methanol were 0.35 +/- 0.03 microM and 2.86 x 10(6) M(-1) respectively, relative to 3.97 +/- 0.47 microM and 0.25 x 10(6) M(-1) respectively, in buffer. Increasing concentrations of cyanine overcame spermine inhibition, demonstrating the reversibility of DNA-drug interactions. LambdaDNA interacted similarly with spermine and cyanine, confirming system flexibility. The model drug, dye and methanol effects are discussed in detail. Cyanine might be a safer alternative to the mutagenic ethidium bromide for investigating DNA-drug interactions.

Antimicrobial, antiparasitic and cytotoxic spermine alkaloids from Albizia schimperiana.

Albizia schimperiana Oliv. (Leguminosae) is a tree distributed in the highland of Kenya, where it is used as a traditional medicine for the treatment of bacterial and parasitic infections, notably pneumonia and malaria, respectively. Bioassay guided isolation of the CH2Cl2-MeOH 1:1/ MeOH-H20 9:1 (mixed) extract of A. schimperiana afforded the new bioactive macrocyclic spermine alkaloid, namely 5,14-dimethylbudmunchiamine L1 (1) and three known budmunchiamine analogs 2-4. The structures of the compounds 1-4 were determined by 1D and 2D NMR data, including COSY, HMQC, and HMBC experiments, and ESI-HRMS. Compounds 1 and 3 exhibited significant in vitro antimicrobial activity against a panel of microorganisms, including C neoformans, methicillin-resistant S. aureus, E. coli, M. intracellulare, and A. fumigatus. In Saddition, they demonstrated strong in vitro antimalarial activities against chloroquine-susceptible (D6) and -resistant (W2) strains of Plasmodium falciparum with IC50s ranging from 120-270 ng/mL. Compounds 1-4 were also evaluated for cytotoxic activity against selected human cancer cell lines and mammalian kidney fibroblasts (VERO cells). It was observed that hydroxyl substitution of the side chain of the budmunchiamines dramatically reduced the cytotoxicity and antimicrobial activity of the alkaloids 2 and 4 without decreasing antimalarial activity.

Letter: characterisation and identification of spermine and spermidine derivatives in Microdesmis keayana and Microdesmis puberula roots by electrospray ionisation tandem mass spectrometry and high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry.

Three new N(1),N(5),N(14)-tris(4- hydroxycinnamoyl)spermines were identified in hydromethanolic root extracts of Microdesmis keayana J. Léonard and Microdesmis puberula Hook f. The electrospray ionisation tandem mass spectrometry (ESI-MS/MS) technique with specific nuclear magnetic resonance analysis of hydrolysed products made it possible to identify N(1),N(5),N(14)-tris(p-coumaroyl)spermine, N(1)-feruloyl,N(5),N(14)-di(p-coumaroyl)spermine and N(1),N(5),N(14)-tris(feruloyl)spermine, named keayanines B, C and D, respectively. ESI-MS/MS analysis most effectively provided structural data although high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry was also used to characterise four other compounds from Microdesmis puberula-keayanidines A, B, C and keayanine A-which had already been identified in M. keayana. This chemical data is the first to be published for M. puberula which is a commonly used plant in Central African traditional medicine.

Effects of Microdesmis keayana roots on sexual behavior of male rats.

In the present study, the aphrodisiac properties of Microdesmis keayana J. Léonard root extract and major isolated alkaloids were evaluated by observing the sexual behavior of male rats. Aqueous extract (150mg/kg body weight) and pure alkaloids (3mg/kg body weight) were administered orally by gavage to male rats. Latent times of observation, intromission and ejaculation, mounting behavior, number of intromissions and mating performances were evaluated and compared to those obtained with untreated rats in the presence of receptive and non-receptive females. The results have shown that aqueous extract and alkaloids of M. keayana stimulate sexual parameters in rats' sexual behavior. A short-term toxicity study undertaken to establish the therapeutic index of aqueous extract, showed that a high dose of the extract (2g/kg body weight) caused no mortality or changes in rats' behavior.

The antiplasmodial activity of spermine alkaloids isolated from Albizia gummifera.

In the present study the methanolic extract of Albizia gummifera was fractionated into various fractions. These fractions were tested against choroquine sensitive (NF54) and resistant (ENT30) strains of Plasmodium falciparum. All other fractions apart from the alkaloidal fraction showed low activity with IC 50 above 3 microg/ml. The alkaloidal fraction exhibited strong activity against NF54 and ENT30 with IC 50 of 0.16+/-0.05 and 0.99+/-0.06 microg/ml, respectively. Five known spermine alkaloids were isolated from the alkaloidal fraction. These alkaloids exhibited activities against NF54 and ENT30 with IC 50 ranging from 0.09+/-0.02 to 0.91+/-0.10 microg/ml. Four of the alkaloids were further evaluated for in vivo activity against rodent malaria parasite Plasmodium berghei. The alkaloids showed percentage chemosuppression of parasitaemia in mice ranging from 43 to 72%. The use of the extracts A. gummifera for treatment of malaria in traditional medicine seems to have a scientific basis.

Specific type of interactions in the quaternary system of Cu(II), adenosine 5'-triphosphate, 1,11-diamino-4,8-diazaundecane and uridine.

Complexation reactions in the quaternary system Cu/ATP/3,3,3-tet/Urd have been studied. The stability constants of the complexes of the Cu(ATP)(3,3,3-tet)H(x)(Urd) type have been determined by computer analysis of the potentiometric titration. On the basis of the results of spectroscopic as well as equilibrium studies, the mode of interactions has been proposed. Metal ions coordinate phosphate groups of ATP and nitrogen atoms of polyamine. It has been established that in the conditions of the complex Cu(ATP)(3,3,3-tet) formation, uridine introduced into the Cu(II)/ATP/3,3,3-tet ternary system is involved in hydrogen bonding with the endocyclic nitrogen atoms N(1) and N(7) of the ATP purine ring and formation of the adduct Cu(ATP)(3,3,3-tet)H(Urd) is observed. Introduction of metal ions into the system changes substantially the mode of interactions between complementary base pairs relative to that proposed in the Watson and Crick model.

Regulatory role of polyamine in the acid phosphatase from potato tubers.

Effects of polyamine and metal ions on the new type of acid phosphatase purified from potato (Solanum tuberosum L. Irish Cobbler) tubers were analyzed. The enzyme belongs to nonspecific acid phosphatase family (EC 3.1.3.2), which hydrolyzes various phosphorylated substrates. The enzyme hydrolyzed inorganic pyrophosphate as a preferred substrate, and exhibited the hyperbolic kinetics with respect to the substrate, inorganic pyrophosphate in the absence of metal cations. Polyamine activated the enzyme effectively by lowering the K(m) value without appreciable changes in the maximal velocity. The most effective polyamines as activators were spermine and spermidine. Mg(2+) ion increased the K(m) value without affecting the maximal velocity of the enzyme, but Ca(2+) ion decreased both the K(m) and V(max) values. Increasing concentrations of spermine also decreased the K(m) value irrespective of Mg(2+) ion included, but gave a constant K(m) and V(max) values in the absence and presence of Ca(2+) ion. Action of spermine and metal ions can be explained by the complex formation with the substrate pyrophosphate. The acid phosphatase from potato can utilize the pyrophosphate-spermine or pyrophosphate-Ca(2+) complex as the preferred substrates. However, the enzyme can use the pyrophosphate-Mg complex with a weak affinity for the active site. Polyamine activates acid phosphatase in the absence and presence of metal cations, and activation by polyamine of the enzyme may contribute to the stimulation of starch biosynthesis and the control of glycolysis/gluconeogenesis by regulating PPi levels in growing potato tubers.

Anti-endotoxin agents. 3. Rapid identification of high-affinity lipopolysaccharide-binding compounds in a substituted polyamine library.

Lipopolysaccharides (LPS), otherwise termed 'endotoxins', are an integral part of the outer leaflet of the outer-membrane of Gram-negative bacteria. Lipopolysaccharides play a pivotal role in the pathogenesis of 'Septic Shock', a major cause of mortality in the critically ill patient, worldwide. The sequestration of circulatory endotoxin may be a viable therapeutic strategy for the prophylaxis and treatment of Gram-negative sepsis. We have earlier shown that the pharmacophore necessary for small molecules to bind LPS involves two protonatable cationic functions separated by about 15 A, permitting the simultaneous interaction with the negatively charged phosphates on lipid A, the toxically active center of endotoxin. In this report, screening of a multi-thousand membered polyamine library through the combined use of computational and bioassay-guided screens resulted in the discovery of two novel classes of LPS-binding agents. These are represented by the 1) spermine sulfonamides and 2) C-aryl-substituted spermine analogs. We present the selection approach, screening results, computational multivariate analyses and initial structure-activity relationship evaluation herein.

Polymorphism of bulged-out residues in HIV-1 RNA DIS kissing complex and structure comparison with solution studies.

All retroviruses encapsidate their genome as a dimer of homologous single-stranded RNAs. The dimerization initiation site (DIS) of human immunodeficiency virus type 1 (HIV-1) is located in the 5'-untranslated region of the viral genome and consists of a hairpin with a 6 nt self-complementary loop sequence. Genomic RNA dimerization, a crucial step for virion infectivity, is promoted by the formation of a loop-loop complex (or kissing complex) between two DIS hairpins. Crystal structures for the subtypes A, B and F of the HIV-1 DIS kissing complex have now been solved at 2.3 A, 1.9 A and 1.6 A, respectively. They revealed a polymorphism of bulged-out residues showing clearly that their conformation is not a mere consequence of crystal packing. They also provide more insights into ion binding, hydration, and RNA conformation and flexibility. In particular, we observed the binding of spermine to the loop-loop helix, which displaced a magnesium cation important for subtype A DIS dimerization. The excellent agreement between X-ray structures and the results of chemical probing and interference data on larger viral RNA fragments shows that the crystal structures are relevant for the DIS kissing complex present in solution and in viral particles. Accordingly, these structures will be helpful for designing new drugs derived from aminoglycoside antibiotics and targeted against the RNA dimerization step of the viral life-cycle.

Expression, crystallization and preliminary X-ray crystallographic analysis of human agmatinase.

Agmatine, which results from the decarboxylation of L-arginine by arginine decarboxylase, is a metabolic intermediate in the biosynthesis of putresine and higher polyamines (spermidine and spermine). Recent studies indicate that agmatine can have several important biochemical effects in humans, ranging from effects on the central nervous system to cell proliferation in cancer and viral replication. Agmatinase catalyses the hydrolysis of agmatine to putresine and urea and is a major target for drug action and development. The human agmatinase gene encodes a 352-residue protein with a putative mitochondrial targeting sequence at the N-terminus. Human agmatinase (residues Ala36-Val352) has been overexpressed as a fusion with both N- and C-terminal purification tags in Escherichia coli and crystallized in the presence of Mn2+ and 1,6-diaminohexane at 297 K using polyethylene glycol 4000 as a precipitant. X-ray diffraction data were collected at 100 K to 2.49 A from a flash-frozen crystal. The crystals are tetragonal, belonging to space group P4(2), with unit-cell parameters a = b = 114.54, c = 125.65 A, alpha = beta = gamma = 90 degrees. Three monomers are likely to be present in the asymmetric unit, giving a crystal volume per protein weight (VM) of 3.66 A3 Da(-1) and a solvent content of 66.4%.

Polyamine derivatives as selective RNaseA mimics.

Site-selective scission of ribonucleic acids (RNAs) has attracted considerable interest, since RNA is an intermediate in gene expression and the genetic material of many pathogenic viruses. Polyamine-imidazole conjugates for site-selective RNA scission, without free imidazole, were synthesized and tested on yeast phenylalanine transfer RNA. These molecules catalyze RNA hydrolysis non-randomly. Within the polyamine chain, the location of the imidazole residue, the numbers of nitrogen atoms and their relative distances have notable influence on cleavage selectivity. A norspermine derivative reduces the cleavage sites to a unique location, in the anticodon loop of the tRNA, in the absence of complementary sequence. Experimental results are consistent with a cooperative participation of an ammonium group of the polyamine moiety, in addition to it's binding to the negatively charged ribose-phosphate backbone, as proton source, and the imidazole moiety as a base. There is correlation between the location of the magnesium binding sites and the RNA cleavage sites, suggesting that the protonated nitrogens of the polycationic chain compete with some of the magnesium ions for RNA binding. Therefore, the cleavage pattern is specific of the RNA structure. These compounds cleave at physiological pH, representing novel reactive groups for antisense oligonucleotide derivatives or to enhance ribozyme activity.