O-methyl Substitution Research Articles

Structural and bioactive characterization of purified polysaccharide from deep-freeze pretreated Sorghum bicolor L. leaf sheath

This study determined the effect of deep-freeze pretreatment of sorghum leaf sheath on the extraction yield of ultrasound-extracted purified polysaccharides (DFUP-1), and confirmed the physicochemical, structural and bioactive characteristics of DFUP-1. Deep-freeze pretreatment induced breaks in the cell walls and resulted in a higher yield (14.35%) of crude polysaccharide extract than without pretreatment (9.23%). The crude extract was purified using DEAE-52 cellulose ion exchange and Sephadex G-100 gel-filtration chromatography to obtain DFUP-1. The 1H and 13C NMR spectra of DFUP-1 showed the presence of β-glycosidic linkages and a substitution at C6 of the sugars which may be O-methyl substitution or due to β (1−6) linkages. Peaks for α-anomeric linkages were not detected. The FTIR spectrum of DFUP-1 confirmed its carbohydrate functional groups. Periodate oxidation and formic acid analysis of DFUP-1 showed 1-, 1–6, 1–2, 1–3 and 1–4 linkages. GC-MS analysis of monosaccharide residues of DFUP-1 showed presence of glucose, galactose, arabinose, mannose and xylose. Congo red assay showed that DFUP-1 was not of triple-helix configuration. The ABTS+ and DPPH radical scavenging assay showed an IC50 of 0.10 mg/mL and 1.19 mg/mL for DFUP-1 respectively. At 0.2 mg/mL DFUP-1 showed anti-inflammatory (anti-egg denaturation) activity of 41.52%. The DFUP-1 sample showed lower inhibitory effect against proliferation of leukemia cells at an IC50 of 37.43 µg/mL compared to curcumin with IC50 of 0.98 µg/mL. Taken together, deep-freeze pretreatment coupled with ultrasound extraction increases yield of sorghum leaf sheath polysaccharides with potential nutraceutical and pharmaceutical applications.

Synthesis and biological evaluation of 4H-benzo[e][1,3]oxazin-4-ones analogues of TGX-221 as inhibitors of PI3Kβ

A novel series of TGX-221 analogues was prepared that include isosteric replacement of the 4H-pyrido[1,2-a]pyrimidin-4-one with a 4H-benzo[e][1,3]oxazin-4-one scaffold. The compounds that included an CH(CH3)NH type linker showed comparable activity to TGX-221 analogues with the isosterism supported by the comparative SAR analysis. The analogues containing an CH(CH3)O linker were less active but still showed useful SAR including a favoured o-methyl substitution.

Discovery of diazahexa/hepta cyclic cage-like compounds with broad-spectrum antifungal activity against Candida and Cryptococcus species.

Invasive fungal infections caused by Candida and Cryptococcus species lead to life threating infections in immunocompromised individuals. Furthermore, increasing incidence of fungal strains resistant to FDA-approved antifungal drugs along with the paucity of antifungal drugs warrants novel drugs to treat invasive fungal infections. In this study, we investigated the antifungal activity of a novel series of diazahexa/hepta cyclic cage-like compounds. Results indicate that compounds with unsubstituted and o-methyl substitution on aryl rings exhibit potent broad-spectrum antifungal activity against various fungal strains. In addition, these compounds showed significant inhibitory activity against Candida hyphae and biofilm formation. Collectively, results from this study indicate that these compounds are promising candidates to develop as novel antifungal drugs to treat drug-resistant fungal infections.

ChemInform Abstract: Torsionally and Hydrophobically Modified 2,3-Diarylindenes as Estrogen Receptor Ligands.

2,3-Diarylindenes are ligands for the estrogen receptor which display intrinsic fluorescence. In order to optimize the receptor binding affinity of these compounds while preserving their desirable fluorescence properties, a series of torsionally modified analogues were prepared. A fluorine or methyl group was introduced on either of the two phenyl substituents ortho to their attachment site to the indene nucleus, in order to increase the out-of-plane twist of the appended rings. The analogues were prepared by the benzylation of appropriate deoxybenzoins, followed by Friedel-Crafts cyclic alkylation-dehydration. Comparison of the X-ray crystal structure of one analogue with unsubstituted analogues confirms the torsional perturbation effected by the ortho substituent. The torsional disposition of the C-2 aryl group in the substituted diphenylindenes is further investigated by UV (absorbance maxima and molar absorptivities), fluorescence (Stokes' shift), and NMR (chemical shifts). These spectroscopic measurements indicate increasing twisting between the C-2 aryl substituent and the indene system according to the following order: 3-ring o-Me-indene 9f less than diphenylindene 15 = 20 degrees less than 3-ring o-F-indene 9c less than 1-Me-indene 16 less than 2-ring o-F-indene 9b less than 2-ring o-Me-indene 9e = 63 degrees. The binding affinity of these analogues to the estrogen receptor was evaluated by a competitive radiometric receptor binding assay. While o-fluoro or o-methyl substitution on the 3-ring increases binding only slightly, binding of the o-fluoro 2-ring analogue is increased ca. 6-fold and the o-methyl analogue 11-fold, giving, in the latter case, a compound with an affinity equivalent to that of estradiol. The increase in binding affinity afforded by ortho substitution correlates with the increase in the torsion angle of the C-2 aryl ring. A thermodynamic evaluation of the receptor fit (Andrews, P. R.; Craik, D. J.; Martin, J. L. J. Med. Chem. 1984, 27, 1648) indicates that, for the o-methyl 2-ring analogue, the effect of the ortho substitution on increasing receptor binding appears to be a combination of increased surface area due to the substituent itself, together with a change in surface area of the ligand that results from the increased torsion of the two aryl rings. An o-fluoro substituent on the 2-ring provides a compromise between the relative planarity required for high fluorescence intensity and the molecular shape needed for increased estrogen receptor binding affinity.(ABSTRACT TRUNCATED AT 400 WORDS)

Photoisomerization ofcis,cis- totrans,trans-1,4-Diaryl-1,3-butadienes in the Solid State: The Bicycle-Pedal Mechanism

The photoisomerizations of crystalline or powdered cis,cis-1,4-diphenyl- and 1,4-di(o-tolyl)-1,3-butadienes (cc-DPB and cc-DTB) to the trans,trans isomers were studied at room temperature. The progress of the reactions was monitored by fluorescence spectroscopy, powder X-ray diffraction, (1)H NMR, and high-performance liquid chromatography. Conversions to the trans,trans isomers were as high as 90% for cc-DPB and 20% for cc-DTB. Formation of the cis,trans isomers, the sole products obtained in solution and in very viscous glassy media at 77 K, is completely suppressed in the solid state. The observed two-bond photoisomerizations are explained by the bicycle-pedal (BP) photoisomerization mechanism. X-ray structure determinations show that o-methyl substitution causes a widening of the phenyl/diene dihedral angles from 40 degrees to 56 degrees and decreases the number of conformers in the crystal from two in cc-DPB to one in cc-DTB. The two conformers of cc-DPB molecules exist in crystals in edge-to-face alternating arrays, one of which has the two phenyls in parallel planes and the other in roughly perpendicular planes. The edge-to-face relationship is maintained in cc-DTB, but only the conformer with the o-tolyl groups in parallel planes is present. The time evolutions of fluorescence spectra measured in the course of the photoreaction show remarkable similarities, despite the different molecular conformations and crystal packing arrangements. Principal component analyses of the spectral matrices indicate the formation of discrete components, suggesting that the two-bond photoisomerizations proceed in stages involving molecules in different microcrystal environments. The structureless appearances of the initial fluorescence spectra show that the reactions are in part diabatic. The BP mechanism can account for the observations if the bicycle-pedal motion began in the excited state, S(1), and were completed in the ground state, S(0). Analysis of void spaces in the crystal lattice reveals much less compact packing of cc-DPB than of cc-DTB molecules, possibly explaining the much higher conversions to photoproduct from cc-DPB.

Evaluation of synthetic oligonucleotides as inhibitors of West Nile virus replication

A series of synthetic oligonucleotide phosphorothioate 15-mers were generated against specific sequences in the West Nile virus RNA genome. These antisense oligonucleotides targeted (1) conserved features of the West Nile virus RNA genome that may be expected to lead to inhibition of virus replication since such features play essential roles in the virus lifecycle; (2) G-quartet oligonucleotides with potential facilitated uptake properties and that also targeted conserved sequences among a range of West Nile virus strains. Several formulations with significant in vitro antiviral activity were found. Among the active oligonucleotides were examples that targeted both C-rich RNA sequences of the West Nile RNA genome as well as recognized conserved sequences key to West Nile virus replication. Since the antiviral activity of the latter oligonucleotides diminished upon 2′- O-methyl substitution, it is likely that their activity involves RNase H-catalyzed RNA degradation. One G-rich oligonucleotide that did not target a West Nile virus RNA sequence also was found. These results suggest the potential of antisense strategies for the control of West Nile virus replication if the attendant problem of oligonucleotide delivery can be adequately addressed.

An important 2'-OH group for an RNA-protein interaction.

We have investigated the role of 2'-OH groups in the specific interaction between the acceptor stem of Escherichia coli tRNA(Cys) and cysteine-tRNA synthetase. This interaction provides for the high aminoacylation specificity observed for cysteine-tRNA synthetase. A synthetic RNA microhelix that recapitulates the sequence of the acceptor stem was used as a substrate and variants containing systematic replacement of the 2'-OH by 2'-deoxy or 2'-O-methyl groups were tested. Except for position U73, all substitutions had little effect on aminoacylation. Interestingly, the deoxy substitution at position U73 had no effect on aminoacylation, but the 2'-O-methyl substitution decreased aminoacylation by 10-fold and addition of the even bulkier 2'-O-propyl group decreased aminoacylation by another 2-fold. The lack of an effect by the deoxy substitution suggests that the hydrogen bonding potential of the 2'-OH at position U73 is unimportant for aminoacylation. The decrease in activity upon alkyl substitution suggests that the 2'-OH group instead provides a monitor of the steric environment during the RNA-synthetase interaction. The steric role was confirmed in the context of a reconstituted tRNA and is consistent with the observation that the U73 base is the single most important determinant for aminoacylation and therefore is a site that is likely to be in close contact with cysteine-tRNA synthetase. A steric role is supported by an NMR-based structural model of the acceptor stem, together with biochemical studies of a closely related microhelix. This role suggests that the U73 binding site for cysteine-tRNA synthetase is sterically optimized to accommodate a 2'-OH group in the backbone, but that the hydroxyl group itself is not involved in specific hydrogen bonding interactions.

Structural Characterization of the O-antigenic Polysaccharide of the Lipopolysaccharide from Rhizobium etli Strain CE3: A UNIQUE O-ACETYLATED GLYCAN OF DISCRETE SIZE, CONTAINING 3-O-METHYL-6-DEOXY-l-TALOSE AND 2,3,4-TRI-O-METHYL-l-FUCOSE

The O-antigenic polysaccharide of the Rhizobium etli CE3 lipopolysaccharide (LPS) was structurally characterized using chemical degradations (Smith degradation and beta-elimination of uronosyl residues) in combination with alkylation analysis, electrospray, and matrix-assisted laser desorption ionization-time of flight mass spectrometry, tandem mass spectrometry, and (1)H COSY and TOCSY nuclear magnetic resonance spectroscopy analyses of the native polysaccharide and the derived oligosaccharides. The polysaccharide was found to be a unique, relatively low molecular weight glycan having a fairly discrete size, with surprisingly little variation in the number of repeating units (degree of polymerization = 5). The polysaccharide is O-acetylated and contains a variety of O-methylated glycosyl residues, rendering the native glycan somewhat hydrophobic. The molecular mass of the major de-O-acetylated species, including the reducing end 3-deoxy-d-manno-2-octulosonic acid (Kdo) residue, is 3330 Da. The polysaccharide is comprised of a trisaccharide repeating unit having the structure -->4)-alpha-d-GlcpA-(1-->4)-[alpha-3-O-Me-6-deoxy-Talp-(1--> 3)]-alpha -l-Fucp-(1-->. The nonreducing end of the glycan is terminated with the capping sequence alpha-2,3, 4-tri-O-Me-Fucp-(1-->4)-alpha-d-GlcpA-(1-->, and the reducing end of the molecule consists of the non-repeating sequence -->3)-alpha-l-Fucp-(1-->3)-beta-d-Manp-(1-->3)-beta-QuiNA cp-(1-->4)-a lpha-Kdop-(2-->, where QuiNAc is N-acetylquinovosamine (2-N-acetamido-2,6-dideoxyglucose). The reducing end Kdo residue links the O-chain polysaccharide to the core region oligosaccharide, resulting in a unique location for a Kdo residue in LPS, removed four residues distally from the lipid A moiety. Structural heterogeneity in the O-chain arises mainly from the O-acetyl and O-methyl substitution. Methylation analysis using trideuteriomethyl iodide indicates that a portion of the 2,3,4-tri-O-methylfucosyl capping residues, typically 15%, are replaced with 2-O-methyl- and/or 2,3-di-O-methylfucosyl residues. In addition, approximately 25% of the 3,4-linked branching fucosyl residues and 10% of the 3-linked fucosyl residues are 2-O-methylated. A majority of the glucuronosyl residues are methyl-esterified at C-6. These unique structural features may be significant in the infection process.

Nitrogen and Oxygen Donors in Nonlinear Optical Materials: Effects of Alkyl vs Phenyl Substitution on the Molecular Hyperpolarizability

The second-order nonlinear optical response of amine and phenol/ether derivatives (1−8) has been evaluated using experimental and theoretical techniques. Electric-field-induced second-harmonic generation (EFISH) measurements establish that N-phenyl substitution of 4-nitroaniline (1) produces a greater increase in molecular hyperpolarizability than N-methyl substitution. In contrast, O-phenyl substitution of 4-nitrophenol (6) produces a smaller increase in hyperpolarizability than O-methyl substitution. Neither the enhancement of hyperpolarizability upon N-phenyl substitution nor the differential substituent effect is anticipated on the basis of qualitative arguments. Careful theoretical analysis using semiempirical sum-over-states and finite field calculations provide explanations for both observed effects.

Nuclease-resistant nucleic acid ligands to vascular permeability factor/vascular endothelial growth factor

Background: Vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) is a potent inducer of new blood vessel growth (angiogenesis) that contributes to the pathology of many angiogenesis-associated disease states such as psoriasis, rheumatoid arthritis and cancer. Few molecular entities capable of binding to VPF/VEGF with high affinity and specificity have been described to date. Results: Nuclease-resistant 2′-amino-2′-deoxypyrimidine nucleotide RNA (2′-aminopyrimidine RNA) ligands that bind to VPF/VEGF with high affinity have been identified by iterative rounds of affinity-selection/amplification from two independent random libraries. The sequence information that confers high affinity binding toVPF/VEGF is contained in a contiguous stretch of 24 nucleotides, 5′- CCCUGAUGGUAGACGCCGGGGUG-3′ (2′-aminopyrimidine nucleotides are designated with italic letters). Of the 14 ribopurines in this minimal ligand, 10 can be substituted with the corresponding 2′-O-methylpurine nucleotides without a reduction in binding affinity to VPF/VEGF. In fact, the 2′ O-methyl substitution at permissive positions leads to a ∼17-fold improvement in the binding affinity to VPF/VEGF The higher affinity results from the reduction in the dissociation rate constant of the 2′-O-methyl-substituted RNA ligand from the protein compared to the unsubstituted ligand. The 2′-O-methyl-substituted minimal ligand, which folds into a bulged hairpin motif, is also more thermally stable than the unsubstituted ligand. Nuclease resistance of the ligand is further improved by the 2′-O-methyl substitutions and the addition of short phosphorothioate caps to the 3′- and 5′-ends. Conclusions: We have used the SELEX ( s ystematic e volution of ligands by e xponential enrichment) process in conjunction with post-SELEX modifications to define a highly nuclease-resistant oligonucleotide that binds to VPF/VEGF with high affinity and specificity.

Triplex Formation of Oligonucleotides Containing 2′‐O‐Methylurldine, 5‐Bromo‐2′‐OMethyluridine and 2′‐0‐Methycytidine

AbstractThe influence of 5‐bromo and 2′‐O‐methyl substitution of pyrimidine bases on nucleic acid triplex formation was examined by thermal denaturation and circular dichroism spectra with the following oligomers: 5′‐(Um) (I, Um = 2′‐O‐methyluridine), 5′‐(BUm)15T (II, BUm = 5‐bromo2′‐O‐metnyluridine), 5′‐(CmUm)6Cm‐T (III, Cm = 2′‐O‐methylcytidine), and 5′‐(CmUm)6Cm T (IV). Both I and II form triplexes with dA16 (A) or 5′‐d(C2A16C2)‐5′‐d(G2T16G2) (D), but III and IV form triplexes with 5′‐d(AG)8 (G). Triplex formation involving two unmodified oligomers, dT16 (T) and 5′‐d(CT)7 (C), was used for comparison. The orders of melting temperatures (Tm) of triplexes were II A II (Tm = 48 °C) > I A I (34 °C) > T A T (22 °C); II D (Tm= 30 °C) > I D (22 °) > T D (12 °C); and IV G IV (Tm= 82 °C) > III G III (72 °C) > C G C (55 °C). The pKa of IVG IV, III G III, and C G C were determined by CD to be 6.5,6.3, and 6.2, respectively. Triplexes formed by oligonucleotides containing both 2′‐O‐methyl and 5‐bromo substitutions are more stable and have a greater pKa than those formed by oligonucleotides with 2′‐O‐methyl substitution only; which in turn are more stable and have a greater pKa than those formed by unmodified oligonucleotides.

Spectroscopic properties of aromatic dicarboximides. Part 2.—Substituent effect on the photophysical properties of N-phenyl-1,2-naphthalimide

Absorption and fluorescence spectra, fluorescence decay times, fluorescence quantum yields and triplet yields have been determined for N-phenyl-1,2-naphthalimide and its phenyl-substituted methyl derivatives in different solvents. N-Phenyl-1,2-naphthalimide emits long-wavelength fluorescence in hexane (λmaxf= 550 nm) which is red shifted by methyl substitution at the meta and para positions of the phenyl ring and by using a solvent of higher polarity. The fluorescence decays on the sub-nanosecond timescale. When the N-phenyl-1,2-naphthalimide has o-methyl substituents in the phenyl group, they emit dual fluorescence. The location of the short-wavelength component is constant while that of the long-wavelength component is blue shifted as a result of o-methyl substitution. Ortho substitution also increases the decay time of the long-wavelength fluorescence. The results are explained in terms of vibronic interaction between the S1(ππ*) and S2(nπ*) excited states (pseudo-Jahn–Teller effect) which is enhanced by solvent relaxation and twisting of the phenyl ring towards a coplanar geometry.

ChemInform Abstract: THE KINETICS OF THE DISPLACEMENT, BY CHLORIDE, OF HETEROCYCLIC NITROGEN BASES (AM) FROM TRANS‐(PTL(AM)CL2) (L = C2H4, CO, OR PME3): THE EFFECT OF STERIC HINDRANCE IN THE LEAVING GROUP ON THE TRANS EFFECT OF L

The kinetics of the reaction, trans-[PtL(am)Cl2]+ Cl– [graphic omitted] [PtLCl3]–+ Ham+(L = C2H4, CO, or PMe3; am = pyridine, 2-methylpyridine, 2,6-dimethylpyridine, or 2,4,6-trimethylpyridine) have been studied in 5% aqueous methanol at 25.0 °C. Only the ethene complexes show a significant dependence on [Cl–] and this is much reduced on o-methyl substitution in the leaving pyridine. In all cases the reactivity is greatly decreased by steric hindrance in the leaving group. The results are discussed in terms of a general destabilisation of the transition state due to steric crowding, together with a specific effect arising from restrictions on the orientation of the ethene molecule in the transition state.

The kinetics of the displacement, by chloride, of heterocyclic nitrogen bases (am) from trans-[PtL(am)Cl2](L = C2H4, CO, or PMe3); the effect of steric hindrance in the leaving group on the trans effect of L

The kinetics of the reaction, trans-[PtL(am)Cl2]+ Cl– [graphic omitted] [PtLCl3]–+ Ham+(L = C2H4, CO, or PMe3; am = pyridine, 2-methylpyridine, 2,6-dimethylpyridine, or 2,4,6-trimethylpyridine) have been studied in 5% aqueous methanol at 25.0 °C. Only the ethene complexes show a significant dependence on [Cl–] and this is much reduced on o-methyl substitution in the leaving pyridine. In all cases the reactivity is greatly decreased by steric hindrance in the leaving group. The results are discussed in terms of a general destabilisation of the transition state due to steric crowding, together with a specific effect arising from restrictions on the orientation of the ethene molecule in the transition state.

Dopamine receptor topography: Characterization of antagonist requirements of striatal dopamine-sensitive adenylate cyclase using protoberberine alkaloids

Representative protoberberine-related alkaloids, i.e. tetrahydroprotoberberines (THPB), quaternary protoberberine salts (Quat. PB) and quaternary dehydroprotoberberine salts (Dehyd. Quat. PB), have been used to characterize the geometric and stereospecific requirements of antagonists of the dopamine receptor. The optical isomers of 2, 3, 10, 11-THPB were tested for their ability to antagonize dopamine stimulated adenylate cyclase activity. The results indicate that (±)-2. 3, 10, 11-THPB inhibited the ability of 100 μM dopamine to elevate adenylate cyclase in homogenates of the rat caudate nucleus. The ic 50 was observed to be 6 μM. The S-(−)-isomer of 2, 3, 10, 11-THPB was a more potent antagonist of dopaminesensitive adenylate cyclase activity than the R-(+)-isomer. The ic 50 for (−)-THPB was 1μM whereas that for the (+)-isomer was 50 μM. The data also show that the positional isomer, 2, 3, 9, 10-THPB, antagonized dopamine activation of adenylate cyclase with the same degree of potency as 2, 3, 10, 11-THPB. Exhaustive O-methylation of THPB at all four hydroxyl positions, the 2, 3-position of the “a” ring and the 10, 11-position of the “d” ring as in xylopinine or the 2, 3-position of the “a” ring and the 9, 10-position of the “d” ring as in tetrahydropalmatine, rendered these compounds weak antagonists of the dopamine response. Selective O-methylation of the THPB molecule markedly altered the potency of the resultant compounds as antagonists depending on the position of the O-methyl substitution. Overall, these data are consistent with the idea that the orientation of the nitrogen atom in a fixed ( cis: gauche) position 2 carbon atoms from a catechol nucleus renders antagonist properties to these compounds which interact with the dopamine receptor.

Interferon induction and its dependence on the primary and secondary structure of poly(inosinic acid).poly(cytidylic acid).

The synthetic interferon (IF) inducer rIn.rCn was modified by substituting the ribosyl residues with either their corresponding deoxy(dC or dI) or 2'-O-methyl analogues (mC or mI). The polynucleotide duplexes of these analogues are inactive as IF inducers. Circular dichroism (CD) studies revealed that, while the deoxy substitution produces significant changes in the conformation of rIn.rCn, the 2'-O-methyl substitution produces no detectable change. Biological competition experiments indicated that the methylated duplexes mIn.rCn, rIn.mCn, and mIn.mCn all compete with rIn.rCn for IF induction, while the deoxy duplexes dIn.rCn and rIn.dCn do not. These results are consistent with those predicted from the CD data. Copolymer duplexes (mI,rI)n.(mC,rC)n of varying degrees of methylation and residue clustering were also evaluated for IF induction in human fibroblasts. The IF-inducing capabilities of these duplexes correlated highly with the presence of clusters containing six or more consecutive ribosyl residues. These combined observations suggest that interaction of rIn.rCn with the cell in the induction process may occur in a biphasic manner involving first the topological recognition of a large segment of the RNA to allow for proper binding to the putative cellular receptor, followed by recognition of a much smaller region of the RNA corresponding to 6--12 consecutive ribosyl residues (0.5 to 1 helical turn) which is responsible for the triggering of the induction process.

An assessment of oxime-oximato hydrogen bonding: A structural and thermodynamic study of copper(II) complexes

Copper(II) complexes formed by the diamine dioxime ligand 4,4,9,9- tetramethyl-5,8-diazadodecane-2,11-dione dioxime (H2dddo) and its O-methyl ether (Hddmo) and bis-O-methyl ether (dddm) have been studied. The log K (potentiometric) and ΔH (calorimetric) values are reported for formation of the four-coordinate complexes [Cu(Hddmo)]2+ and [Cu(dddm)]2+ and for the deprotonation of [Cu(Hddmo)]2+ to give [Cu(ddmo)]+ at 25°C, I = 0.1 M NaCl. (log K = 12.11 � 0.04, 9.10�0.02 and -6.76�0.09; ΔH= -43�2, -17.9�0.4 and +21.9�0.9 kJ mol-1 respectively.) Comparison with data for [Cu(H2dddo)]2+ and [Cu(Hdddo)]+ affords information about the relative contributions of (i) oxime deprotonation (c. 105.6), and (ii) oxime oximato hydrogen bonding (c. 103.5), to the stability of these (non-conjugated) dioxime complexes. The formation of intramolecular (oxime-oximato) hydrogen bonds is favoured by a positive ΔS; intermolecular bonds (oximato-solvent) give rise to a negative ΔS. ��� A single-crystal X-ray molecular structure determination is reported for the complex Cu(dddm)-(ClO4)2. In the solid state the complex cation is square pyramidal with one perchlorate ion weakly coordinated in the apical position and the four nitrogen donor atoms forming a distorted square plane about the copper atom. Steric effects associated with O-methyl substitution are assessed. Steric hindrance between adjacent =NOR groups does not increase measurably when =NOH is replaced by =NOMe.

Effects of o-methyl substitution on the pharmacological properties of 1,1-dimethyl-4-phenylpiperazinium.

Effects of o-Methyl Substitution on the Pharmacological Properties of 1,1-Dimethyl-4-phenylpiperazinium

THE ALKALI-STABLE DINUCLEOTIDE SEQUENCES IN 18S+28S RIBONUCLEATES FROM WHEAT GERM.

The 2′-O-methyl substitution of ribose residues of ribonucleate chains can give rise to 16 alkali-stable dinucleotides having the general structure NxpNp in which N is any of the four major ribonucleosides and Nx is the 2′-O-methyl derivative of any of the four major ribonucleosides. Quantitative data are presented which show that all of these 16 alkali-stable dinucleotides occur in characteristic amounts in alkali hydrolyzates of the 18 S + 28 S ribonucleates from wheat germ. The alkali-stable dinucleotides cumulatively account for 3 mole% of the total nucleotides of the 18 S + 28 S wheat germ ribonucleates. The relative amounts of the four 2′-O-methyl ribosides responsible for the alkali stability of the dinucleotides have been shown to be distinctly different from the relative amounts of the four corresponding normal ribosides which participate in either the alkali-stable dinucleotide sequences or in the ribonucleate chains as a whole. Quantitative end group data show that the alkali-stable dinucleotide sequences occur internally in high molecular weight ribonucleate chains. Preliminary data are presented on the occurrence of alkali-stable trinucleotides in alkali hydrolyzates of the 18 S + 28 S wheat germ ribonucleates.

THE SEPARATION, ESTIMATION, AND CHARACTERIZATION OF ALKALI-STABLE OLIGONUCLEOTIDES DERIVED FROM COMMERCIAL RIBONUCLEATE PREPARATIONS

Methods are described which are suitable for the quantitative analysis of the alkali-stable oligonucleotides which result from the hydrolysis of ribonucleates in molar alkali at room temperature for 90 hours. The alkali-stability of the oligonucleotides is presumed to result from 2′-O-methyl substitution of ribose residues and this assumption is supported by the relatively slight reactivity of the purine 2′-O-methyl ribosides in the orcinol color reaction for pentoses. The existence of all of the 16 possible dinucleotides as part of ribonucleate chains has been established. The quantity of alkali-stable trinucleotides is much greater than would be expected for a random spatial distribution of 2′-O-methyl ribosides in ribonucleate chains.