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Ruthenium complexes of 1,4-diazabutadiene ligands with a cis-RuCl2 moiety for catalytic acceptorless dehydrogenation of alcohols: DFT evidence of chemically non-innocent ligand participation† † Electronic supplementary information (ESI) available: Crystallographic data for trans-1 and cis-1 (Table S1), trans-2 and cis-2 (Table S2), trans-3 and cis-3 (Table S3), trans-4 and cis-4 (Table S4); Crystal structure of trans-1, trans-2 and trans-4 (Fig. S1); crystal structure of cis-1, cis-2 and cis-4 (Fig. S2); selected bond parameters for trans-1 and cis-1 (Table S5); selected bond parameters for trans-2 and cis-2 (Table S6); selected bond parameters for trans-3 and cis-3 (Table S7); selected bond parameters for trans-4 and cis-4 (Table S8); cyclic voltammetric data of trans-isomers and cis-isomers (Table S9); cyclic voltammogram of cis-3 (Fig. S3); least-squares plot of E1⁄2 values of Ru(ii)–Ru(iii) couple versus Hammett substituent constant (4σ) for the trans-isomers and the cis-isomers (F

ABSTRACT: The acceptorless dehydrogenative coupling (ADC) of primary alcohols to esters by diazabutadiene-coordinated ruthenium compounds is reported. Treatment of cis-Ru(dmso)4Cl2 in acetone at 56 °C with different 1,4-diazabutadienes [p-XC6H4N

SUBMITTER: Mukherjee A

PROVIDER: S-EPMC10463240 | biostudies-literature | 2023 Aug

REPOSITORIES: biostudies-literature

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Project description:Free in solution, the immunosuppressive compounds cyclosporin A (CsA), FK506, ascomycin and rapamycin are present in many solvents in various slowly interconverting conformations. Together with their cellular receptor proteins, cyclophilin (CyP) and FK506-binding protein (FKBP), however, these inhibitors have been shown to have a homogeneous conformation. The existence of a slow cis-trans interconversion of an imidic bond in the inhibitor molecule during the course of the formation of the CsA-CyP18cy complex (where CyP18cy is human 18 kDa cytosolic CyP) prompted us to investigate the reaction of the peptidomacrolides FK506, ascomycin and rapamycin with two specific binding-proteins in more detail. Since formation of the FK506-FKBP complex results in the inhibition of the peptidylprolyl cis-trans-isomerase activity of the binding protein, we used the enzyme's decrease in enzymic activity to monitor binding of the inhibitors to their enzyme targets. For FK506, the kinetics of inhibition of human 12 kDa cytosolic FKBP (FKBP12cy) were clearly dependent on time. Subsequent to a rapid inactivation reaction, not resolved in its kinetics due to manual mixing, a slow dominant first-order inactivation process with a relaxation time of 1163 s at 10 degrees C was observed. Concomitantly the Ki value of the slow phase dropped 2.6-fold within the first 60 min of incubation. Using the FKBP12cy homologue 25 kDa membrane FKBP (FKBP25mem), a bacterial peptidylprolyl cis-trans-isomerase, the rate and amplitudes of the inhibition reactions were very similar to FKBP12cy. On the other hand, the kinetics and amplitudes of the inhibition of FKBP12cy varied significantly if rapamycin was used as an inhibitor instead of FK 506. Owing to reduced conformation transition in rapamycin upon binding to FKBP12cy, the slow phase during inhibition was significantly decreased in amplitude. A likely reason for this became apparent when the activation-enthalpy and the pH-dependence of the rate constants of the slow phase were determined. We conclude that the cis to trans interconversion of the pipecolinyl bond of the three peptidomacrolides may be responsible for the slow process. There was no indication of a suicide catalysis of this process by FKBPs.

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