Acetoxonium ions from acetoxyoxiranes and orthoesters: their conversion into ethylidene acetals,rearrangement, and solvolysis

The acid-catalysed ethylidenation of some methyl pentopyranosides has been studied and the configuration at the acetal carbon atom assigned by p.m.r. spectroscopy. There is a strong preference for the isomer in which the methyl group has the endo configuration. Several cyclic alkyl orthoacetates derived from methyl pentopyranosides have been prepared by orthoester exchange and the endo C-methyl isomer shown to preponderate. Treatment of vicinal acetoxyoxiranes and orthoacetates with boron trifluoride followed by lithium borohydride, or with diborane, yields ethylidene acetals in which the C-methyl group is endo. Rearrangements of the hexachloroantimonate salts of acetoxonium ions derived from methyl lyxo- and arabino-pyranosides, possessing trans-vicinal acetoxyl groups, have been studied. The ions having the arabino configuration are preferred in both the α and β series. The reaction of cyclic orthoacetates of methyl β-L-arabinopyranoside and some derivatives with dry acetic acid proceeds via an acyclic acetoxonium ion to yield only products having the L-arabino configuration.     

Selectively blocked derivatives of muco-inositol and their conversion into derivatives of epi- and cis-inositol.

Benzylation, and then hydrolysis, of 1, 2:4, 5-di-O-isopropylidene-muco-inositol (1) gave 3, 6-di-O-benzyl-muco-inositol (3). This was converted into a series of derivatives, including the 1, 5-di-O-benzoyl-3, 6-di-O-benzyl-2, 4-di-p-toluenesulfonate 7. The resistance to displacement of the sulfonate groups in 7 prevented conversion of 7 into an intermediate for the synthesis of aminoglycoside antibiotics. Monobenzylation of 1, followed by an oxidation-reduction cycle, yielded 6-O-benzyl-1, 2:4, 5-di-O-isopropylidene-epi-inositol (10). From this was synthesized a series of epi-inositol derivatives, analogous to the muco series but less complete. For derivatives of 1, 2:5, 6-di-O-isopropylidene-epi- and muco-inositol, the p. m. r. data indicate modified skew conformations. The reaction of the 3, 6-di-p-bromobenzenesulfonate (17) of 1 with anhydrous hydrazine proceeded in part by S-O cleavage to regenerate 1, and in part by displacement of both sulfonate groups by the same nitrogen atom. The resulting, novel 1, 4-epimino-cis-inositol was converted into further derivatives.     

Synthesis and evaluation of methyl ether derivatives of the vancomycin, teicoplanin, and ristocetin aglycon methyl esters

A series of methyl ether derivatives of the vancomycin, teicoplanin, and ristocetin aglycon methyl esters was synthesized and their antimicrobial activity was established. These derivatives exhibit increased activity against VanB resistant strains of bacteria equipotent with that observed with sensitive bacteria.     

Synthesis, topoisomerase I inhibition and antitumor cytotoxicity of 2,2':6',2"-, 2,2':6',3"- and 2,2':6',4"-terpyridine derivatives

For the development of new anticancer agents, 2,2':6',2"-, 2,2':6',3"- and 2,2':6',4"-terpyridine derivatives were designed and evaluated for their topoisomerase I inhibitory activity and antitumor cytotoxicity. Structure-activity relationship studies indicated that 2,2':6',2"-terpyridine derivatives were highly cytotoxic toward several human tumor cell lines, whereas 2,2':6',3"- and 2,2':6',4"-terpyridine derivatives were potent topoisomerase I inhibitors.     

The conversion of 3' UTRs into coding regions

A possible origin of novel coding sequences is the removal of stop codons, leading to the inclusion of 3' untranslated regions (3' UTRs) within genes. We classified changes in the position of stop codons in closely related Saccharomyces species and in a mouse/rat comparison as either additions to or subtractions from coding regions. In both cases, the position of stop codons is highly labile, with more subtractions than additions found. The subtraction bias may be balanced by the input of new coding regions through gene duplication. Saccharomyces shows less stop codon lability than rodents, probably due to greater selective constraint. A higher proportion of 3' UTR incorporation events preserve frame in Saccharomyces. This higher proportion is consistent with the action of the [PSI(+)] prion as an evolutionary capacitor to facilitate 3' UTR incorporation in yeast.     

Synthesis and bioactivity of C-2 and C-3 methyl ether derivatives of brassinolide

The following six novel methyl ether derivatives of brassinolide were prepared and their brassinosteroid activity was measured by means of the rice leaf lamina inclination bioassay: 2-O-methylbrassinolide, 3-O-methylbrassinolide, 2,22,23-tri-O-methylbrassinolide, 3,22,23-tri-O-methylbrassinolide, 2-O-methyl-25-methoxybrassinolide and 3-O-methyl-25-methoxybrassinolide. Brassinolide was used as a standard for comparison. All six compounds were also tested in the presence of 1000 ng of indole-3-acetic acid (IAA), an auxin that synergizes the effects of brassinosteroids. The 2-O-methyl- and 3-O-methylbrassinolide derivatives showed weak activity at high doses, which was enhanced by IAA, especially in the case of the 3-O-methyl derivative. Similarly, the 2,22,23-tri-O-methyl- and 3,22,23-tri-O-methyl derivatives displayed weak bioactivity on their own, but significantly stronger activity when applied with IAA. The 3-O-methyl and 3,22,23-tri-O-methyl analogues plus IAA were comparable in bioacivity to brassinolide alone, but were less active than brassinolide plus IAA. In each case, O-methylation at C-2 resulted in a greater loss of activity than O-methylation at C-3 under the same conditions. The relatively strong activity of 3,22,23-tri-O-methylbrassinolide in the presence of IAA is especially noteworthy as it indicates that free hydroxyl groups at C-3, C-22, and C-23 are not essential for bioactivity. Finally, 2-O-methyl- and 3-O-methyl-25-methoxybrassinolide were essentially inactive alone, and showed only a modest increase in bioactivity when coapplied with IAA.     

Carbon conversion efficiency and limits of productive bacterial degradation of methyl tert-butyl ether and related compounds

The utilization of the fuel oxygenate methyl tert-butyl ether (MTBE) and related compounds by microorganisms was investigated in a mainly theoretical study based on the Y(ATP) concept. Experiments were conducted to derive realistic maintenance coefficients and K(s) values needed to calculate substrate fluxes available for biomass production. Aerobic substrate conversion and biomass synthesis were calculated for different putative pathways. The results suggest that MTBE is an effective heterotrophic substrate that can sustain growth yields of up to 0.87 g g(-1), which contradicts previous calculation results (N. Fortin et al., Environ. Microbiol. 3:407-416, 2001). Sufficient energy equivalents were generated in several of the potential assimilatory routes to incorporate carbon into biomass without the necessity to dissimilate additional substrate, efficient energy transduction provided. However, when a growth-related kinetic model was included, the limits of productive degradation became obvious. Depending on the maintenance coefficient m(s) and its associated biomass decay term b, growth-associated carbon conversion became strongly dependent on substrate fluxes. Due to slow degradation kinetics, the calculations predicted relatively high threshold concentrations, S(min), below which growth would not further be supported. S(min) strongly depended on the maximum growth rate mu(ma)(x), and b and was directly correlated with the half maximum rate-associated substrate concentration K(s), meaning that any effect impacting this parameter would also change S(min). The primary metabolic step, catalyzing the cleavage of the ether bond in MTBE, is likely to control the substrate flux in various strains. In addition, deficits in oxygen as an external factor and in reduction equivalents as a cellular variable in this reaction should further increase K(s) and S(min) for MTBE.     

Prevention of overoxidation in periodate oxidation of reducing oligosaccharides by their conversion into 1,5-anhydroalditol derivatives

A procedure for the conversion of reducing oligosaccharides into their 1,5-anhydroalditol derivatives was devised to prevent overoxidation during periodate oxidation. Gas-chromatographic analysis of the aldehydes in the products of complete oxidation of the resultant 1,5-anhydroalditol derivatives by the dithioacetal method^1b indicated that new types of dialdehyde characteristic of the linkage-types were formed, together with ordinary simple aldehydes. A number of d-gluco-oligosaccharides having various types of interglycosidic linkage were examined by this method. The results were consistent with expectations.     

Zinc triflate-benzoyl bromide: a versatile reagent for the conversion of ether into benzoate protecting groups and ether glycosides into glycosyl bromides

A simple and efficient method is developed for the chemoselective one-pot conversion of ethers (benzyl, TBDMS and acetal) to the corresponding benzoates by zinc triflate-catalyzed deprotection and benzoylation by benzoyl bromide. In the same reaction, methyl or p-methoxyphenyl glycosides are converted into glycosyl bromides that are useful in glycosylation reactions.     

The constituents of solorina crocea: Averythrin 6-monomethyl ether and methyl gyrophorate

The anthraquinone averythrin 6-monomethyl ether (III) and the depside methyl gyrophorate (V) were isolated from the lichen Solorina crocea (L.) Ach.     

Synthetic receptor analogues: preparation and calculated conformations of the 2-deoxy, 6-O-methyl, 6-deoxy, and 6-deoxy-6-fluoro derivatives of methyl 4-O-alpha-D-galactopyranosyl-beta-D-galactopyranoside (methyl beta-D-galabioside)

The 2-deoxy (7), 6-O-methyl (15), 6-deoxy (22), and 6-deoxy-6-fluoro (31) derivatives of methyl beta-D-galabioside (1) have been synthesised. Thus, 7 was prepared by xanthate reduction using tributyltin hydride, whereas 22 was obtained by catalytic hydrogenation of a 6-deoxy-6-iodogalabioside. Regioselective monofluorination of methyl 2,3-di-O-benzoyl-beta-D-galactopyranoside with Et2NSF3 and subsequent alpha-D-galactosylation provided 31. Molecular mechanics calculations yielded similar conformations for 1, 7, 15, 22, and 31 with differences in phi H and psi H of less than 5 degrees. No indications of intramolecular hydrogen bonds, as displayed by 1 in the crystal, were found for 7, 15, 22, or 31.     

A sensitive and specific enzyme immunoassay for the detection of methyl ether derivatives of cyclomaltoheptaose

We have raised antibodies against two methylated derivatives of beta-CD, heptakis(2,6-di-O-methyl)cyclomaltoheptaose (Dimeb) and heptakis(2,3,6-tri-O-methyl)cyclomaltoheptaose (Trimeb). These antibodies were used to develop two specific and sensitive enzyme immunoassays, presenting a detection limit close to 500 and 30 pg/mL for Trimeb and Dimeb, respectively. Cross reactivities of different linear and cyclic maltooligosaccharides were investigated, demonstrating a high specificity against the structural features of the secondary hydroxyls rim. Several commercial Dimeb samples, containing different mixtures of partially methylated beta-cyclodextrin derivatives including RAMEB, which contains only a few amount of pure Dimeb, could be easily evaluated by the Dimeb immunoassay. Both of these assays have been shown to allow accurate measurement in plasma and urine, thus appearing as useful tools for further applications in biological material.     

Studies on griseolic acid derivatives. I. Synthesis of substituted derivatives of griseolic acid at the N1, C6, C2' or C7' position and their biological activities

Griseolic acid derivatives having a different substituent at the N1,C6,C2' or C7' position of the natural product were synthesized and their structure activity relationship to cyclic nucleotide phosphodiesterase inhibitory activity was investigated.     

3',5' Cyclic nucleotide phosphodiesterase from human platelets: effect of heat upon the multiple forms and their interconversion

A 33,000 g supernatant from human platelets showed a biphasic heat inactivation curve at 45, 50 and 55 degrees C of the cAMP and cGMP phosphodiesterase. This could suggest the presence of two differently heat sensitive phosphodiesterases. However, a preparation heated for 30 min at 55 degrees C, where only the apparently thermostable form of the enzyme remained, still displayed the same characteristics as the starting material, i.e. two apparent Km values for cAMP, a cAMP specific activity lower at low protein concentration (less than 50 micrograms/ml) than at high protein concentration(greater than 100 micrograms/ml), and three peaks of activity upon linear sucrose density gradient. Moreover, a biphasic inactivation curve was again observed after a second heat treatment. These results demonstrated that the heat effect is not a simple protein denaturation of one of two independent species. A study at different temperatures of the profile of the cAMP phosphodiesterase upon sucrose gradient demonstrated that the dissociated form was predominant at high temperature whereas lower temperature favored the associated form. During heat treatment, the dissociated form is at first denatured and this leads to a shift in the equilibrium between the associated and dissociated forms of the phosphodiesterase in favor of the dissociated form. From the overall results, one can draw a model for phosphodiesterase regulation by dissociation-reassociation.     

Mechanisms of inactivation of human S-adenosylhomocysteine hydrolase by 5',5',6',6'-tetradehydro-6'-deoxy-6'-halohomoadenosines

In an effort to design more specific and potent inhibitors of S-adenosylhomocysteine (AdoHcy) hydrolase, we investigated the mechanisms by which 5',5',6', 6'-tetradehydro-6'-deoxy-6'-halohomoadenosines (X = Cl, Br, I) inactivated this enzyme. The 6'-chloro (a) and 6'-bromo (b) acetylenic nucleoside analogues produced partial ( approximately 50%) loss of enzyme activity with a concomitant ( approximately 50%) reduction of E-NAD(+) to E-NADH. In addition, Ade and halide ions were released from the inhibitors in amounts suggestive of a process involving enzyme catalysis. AdoHcy hydrolase, which was inactivated with compound a, was shown to contain 2 mol of the inhibitor covalently bound to Lys318 of two subunits of the homotetramer. These data suggest that the enzyme-mediated water addition at the 5' position of compound a or b produces an alpha-halomethyl ketone intermediate, which is then attacked by a proximal nucleophile (i.e., Lys318) to form the enzyme-inhibitor covalent adduct (lethal event); in a parallel pathway (nonlethal event), addition of water at the 6' position produces an acyl halide, which is released into solution and chemically degrades into Ade, halide ion, and sugar-derived products. In contrast, compound c completely inactivated AdoHcy hydrolase by converting 2 equiv of E-NAD(+) to E-NADH and causing the release of 2 equiv of E-NAD(+) into solution. Four moles of the inhibitor was shown to be tightly bound to the tetrameric enzyme. These data suggest that compound c inactivates AdoHcy hydrolase by a mechanism similar to the acetylenic analogue of Ado described previously by Parry et al. [(1991) Biochemistry 30, 9988-9997].     

The enzymatic conversion of 3'-phosphate terminated RNA chains to 2',3'-cyclic phosphate derivatives

The enzyme, RNA cyclase, has been purified from cell-free extracts of HeLa cells approximately 6000-fold. The enzyme catalyzes the conversion of 3'-phosphate ends of RNA chains to the 2',3'-cyclic phosphate derivative in the presence of ATP or adenosine 5'-(gamma-thio)triphosphate (ATP gamma S) and Mg2+. The formation of 1 mol of 2',3'-cyclic phosphate ends is associated with the disappearance of 1 mol of 3'-phosphate termini and the hydrolysis of 1 mol of ATP gamma S to AMP and thiopyrophosphate. No other nucleotides could substitute for ATP or ATP gamma S in the reaction. The reaction catalyzed by RNA cyclase was not reversible and exchange reactions between [32P]pyrophosphate and ATP were not detected. However, an enzyme-AMP intermediate could be identified that was hydrolyzed by the addition of inorganic pyrophosphate or 3'-phosphate terminated RNA chains but not by 3'-OH terminated chains or inorganic phosphate. 3'-[32P](Up)10Gp* could be converted to a form that yielded, (Formula: see text) after degradation with nuclease P1, by the addition of wheat germ RNA ligase, 5'-hydroxylpolynucleotide kinase, RNA cyclase, and ATP. This indicates that the RNA cyclase had catalyzed the formation of the 2',3'-cyclic phosphate derivative, the kinase had phosphorylated the 5'-hydroxyl end of the RNA, and the wheat germ RNA ligase had catalyzed the formation of a 3',5'-phosphodiester linkage concomitant with the conversion of the 2',3'-cyclic end to a 2'-phosphate terminated residue.