“…Ligands 1 − 6 were obtained in N -Boc-protected form ( 14 − 19 ) by treating an appropriate bis(bromomethyl)benzene, 4,4‘-bis(chloromethyl)biphenyl, 2,6-(tosyloxy)pyridine, or 1,3,5-tris(bromomethyl)benzene in dimethylformamide (DMF) with the oxyanion of 13 (Scheme ). The Boc groups were removed by acid-catalyzed hydrolysis, which gave 1 − 6 as hydrochloric salts.…”
Section: Resultsmentioning
confidence: 99%
“…No precipitation of zinc hydroxide was observed, even at pH < 7, indicating that the binding of Zn 2+ to the ligand was virtually quantitative. The pH values at 90 °C were obtained by extrapolation based on the known temperature dependence of the p K a value of HEPES …”
Five dinucleating ligands (1-5) and one trinucleating ligand (6) incorporating 1,5,9-triazacyclododecan-3-yloxy groups attached to an aromatic scaffold have been synthesized. The ability of the Zn(2+) complexes of these ligands to promote the transesterification of dinucleoside 3',5'-monophosphates to a 2',3'-cyclic phosphate derived from the 3'-linked nucleoside by release of the 5'-linked nucleoside has been studied over a narrow pH range, from pH 5.8 to 7.2, at 90 degrees C. The dinuclear complexes show marked base moiety selectivity. Among the four dinucleotide 3',5'-phosphates studied, viz. adenylyl-3',5'-adenosine (ApA), adenylyl-3',5'-uridine (ApU), uridylyl-3',5'-adenosine (UpA), and uridylyl-3',5'-uridine (UpU), the dimers containing one uracil base (ApU and UpA) are cleaved up to 2 orders of magnitude more readily than those containing either two uracil bases (UpU) or two adenine bases (ApA). The trinuclear complex (6), however, cleaves UpU as readily as ApU and UpA, while the cleavage of ApA remains slow. UV spectrophotometric and (1)H NMR spectroscopic studies with one of the dinucleating ligands (3) verify binding to the bases of UpU and ApU at less than millimolar concentrations, while no interaction with the base moieties of ApA is observed. With ApU and UpA, one of the Zn(2+)-azacrown moieties in all likelihood anchors the cleaving agent to the uracil base of the substrate, while the other azacrown moiety serves as a catalyst for the phosphodiester transesterification. With UpU, two azacrown moieties are engaged in the base moiety binding. The catalytic activity is, hence, lost, but it can be restored by addition of a third azacrown group on the cleaving agent.
“…Ligands 1 − 6 were obtained in N -Boc-protected form ( 14 − 19 ) by treating an appropriate bis(bromomethyl)benzene, 4,4‘-bis(chloromethyl)biphenyl, 2,6-(tosyloxy)pyridine, or 1,3,5-tris(bromomethyl)benzene in dimethylformamide (DMF) with the oxyanion of 13 (Scheme ). The Boc groups were removed by acid-catalyzed hydrolysis, which gave 1 − 6 as hydrochloric salts.…”
Section: Resultsmentioning
confidence: 99%
“…No precipitation of zinc hydroxide was observed, even at pH < 7, indicating that the binding of Zn 2+ to the ligand was virtually quantitative. The pH values at 90 °C were obtained by extrapolation based on the known temperature dependence of the p K a value of HEPES …”
Five dinucleating ligands (1-5) and one trinucleating ligand (6) incorporating 1,5,9-triazacyclododecan-3-yloxy groups attached to an aromatic scaffold have been synthesized. The ability of the Zn(2+) complexes of these ligands to promote the transesterification of dinucleoside 3',5'-monophosphates to a 2',3'-cyclic phosphate derived from the 3'-linked nucleoside by release of the 5'-linked nucleoside has been studied over a narrow pH range, from pH 5.8 to 7.2, at 90 degrees C. The dinuclear complexes show marked base moiety selectivity. Among the four dinucleotide 3',5'-phosphates studied, viz. adenylyl-3',5'-adenosine (ApA), adenylyl-3',5'-uridine (ApU), uridylyl-3',5'-adenosine (UpA), and uridylyl-3',5'-uridine (UpU), the dimers containing one uracil base (ApU and UpA) are cleaved up to 2 orders of magnitude more readily than those containing either two uracil bases (UpU) or two adenine bases (ApA). The trinuclear complex (6), however, cleaves UpU as readily as ApU and UpA, while the cleavage of ApA remains slow. UV spectrophotometric and (1)H NMR spectroscopic studies with one of the dinucleating ligands (3) verify binding to the bases of UpU and ApU at less than millimolar concentrations, while no interaction with the base moieties of ApA is observed. With ApU and UpA, one of the Zn(2+)-azacrown moieties in all likelihood anchors the cleaving agent to the uracil base of the substrate, while the other azacrown moiety serves as a catalyst for the phosphodiester transesterification. With UpU, two azacrown moieties are engaged in the base moiety binding. The catalytic activity is, hence, lost, but it can be restored by addition of a third azacrown group on the cleaving agent.
“…The preparative scope of the cyclization reaction was extended to the synthesis of a great variety of 2-alkylidene-3iminoindoles. [15][16][17] A number of substituents could be introduced both at the exocyclic double bond and at the indole moiety by variation of the substituents of the nitrile and of 8, respectively.…”
Section: Nitrile Dianionsmentioning
confidence: 99%
“…The high E -diastereoselectivity is a result of the steric interaction between the bulky arylimino and the phenyl group. The preparative scope of the cyclization reaction was extended to the synthesis of a great variety of 2-alkylidene-3-iminoindoles. − A number of substituents could be introduced both at the exocyclic double bond and at the indole moiety by variation of the substituents of the nitrile and of 8 , respectively. 7 Cyclization of Dilithiated Phenylacetonitrile with Oxalic Acid-Bis(imidoyl) dichlorides (Mechanism A)…”
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