- A hetero diels-alder access to (Z)-zeatin and (Z)-isozeatin
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(Z)-6-(4-Hydroxy-3-methylbut-2-en-1-ylamino)purine, (Z)-zeatin, and the isomeric (Z)-isozeatin, both free from the E isomers, were prepared using the cycloaddition of the in situ generated tert-butyl nitrosoformate on isoprene. A mixture of tert-butyl 5(and 4)-methyl-3,6-dihydro-2H-1,2-oxazine-2-carboxylates thus formed was deprotected and reductively cleaved to (Z)-4-amino-2(and 3)-methylbut-2-en-1-ols, which were chromatographically separated and finally alkylated with 6-chloropurine to give the title compounds.
- Tolman, Vladimir,Hanus, Jan,Sedmera, Petr
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- Peroxide-shunt substrate-specificity for the Salmonella typhimurium O 2-dependent tRNA modifying monooxygenase (MiaE)
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Post-transcriptional modifications of tRNA are made to structurally diversify tRNA. These modifications alter noncovalent interactions within the ribosomal machinery, resulting in phenotypic changes related to cell metabolism, growth, and virulence. MiaE is a carboxylate bridged, nonheme diiron monooxygenase, which catalyzes the O2-dependent hydroxylation of a hypermodified-tRNA nucleoside at position 37 (2-methylthio-N6- isopentenyl-adenosine(37)-tRNA) [designated ms2i6A 37]. In this work, recombinant MiaE was cloned from Salmonella typhimurium, purified to homogeneity, and characterized by UV-visible and dual-mode X-band EPR spectroscopy for comparison to other nonheme diiron enzymes. Additionally, three nucleoside substrate-surrogates (i6A, Cl2i6A, and ms2i6A) and their corresponding hydroxylated products (io6A, Cl2io 6A, and ms2io6A) were synthesized to investigate the chemo- and stereospecificity of this enzyme. In the absence of the native electron transport chain, the peroxide-shunt was utilized to monitor the rate of substrate hydroxylation. Remarkably, regardless of the substrate (i6A, Cl2i6A, and ms2i6A) used in peroxide-shunt assays, hydroxylation of the terminal isopentenyl-C4-position was observed with >97% E-stereoselectivity. No other nonspecific hydroxylation products were observed in enzymatic assays. Steady-state kinetic experiments also demonstrate that the initial rate of MiaE hydroxylation is highly influenced by the substituent at the C2-position of the nucleoside base (v0/[E] for ms2i6A > i 6A > Cl2i6A). Indeed, the >3-fold rate enhancement exhibited by MiaE for the hydroxylation of the free ms 2i6A nucleoside relative to i6A is consistent with previous whole cell assays reporting the ms2io6A and io6A product distribution within native tRNA-substrates. This observation suggests that the nucleoside C2-substituent is a key point of interaction regulating MiaE substrate specificity.
- Corder, Andra L.,Subedi, Bishnu P.,Zhang, Siai,Dark, Amanda M.,Foss Jr., Frank W.,Pierce, Brad S.
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p. 6182 - 6196
(2013/10/01)
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- Syntheses of cis-zeatin and its 9-(2-deoxy-β-D-ribofuranosyl) derivative: A novel synthetic route to the side chain at C(6), and cytokinin activity
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cis-Zeatin (3a) and its 9-(2-deoxy-β-D-ribofuranosyl) derivative (3c) have been synthesized from N-[(1,1-dimethylethoxy)carbonyl]glycine methyl ester (5) in 5 steps by adopting the 'α-amino aldehyde/olefination' technology. The new cis-zeatin derivative (3c), its trans isomer (1c), and known trans-zeatin 9-β-D-riboside (1b) were tested for cytokinin activity in the stimulation of chlorophyll biosynthesis in etiolated cucumber cotyledons. The ribeside 1b turned out to be the most active cytokinin among them, while the deoxyribosides 1c and 3c showed a marked decrease and a total loss, respectively, of cytokinin activity.
- Evidente,Piccialli,Sisto,Ohba,Honda,Fujii
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p. 1937 - 1939
(2007/10/02)
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- Cytokinin metabolism and the modulation of cytokinin activity in radish
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The metabolism of zeatin, N6-(Δ2-isopentenyl) adenine, dihydrozeatin, zeatin-O-glucoside and dihydrozeatin-O-glucoside has been studied using derooted radish seedlings. The metabolites were identified by UV and GC/MS. The patterns of metabolism are compared and provide evidence that the O-glucosyl conjugates may be storage forms of the cytokinins.
- McGaw, Brian A.,Horgan, Roger,Heald, Jim K.
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