Dataset Information

Scandium Reduced Arene Complex: Protonation and Reaction with Azobenzene.

ABSTRACT: The reactivity of the reduced anthracene complex of scandium [Li(thf)₃ ][Sc{N(tBu)Xy}₂ (anth)] (2-anth-Li) (Xy=3,5-Me₂ C₆ H₃ ; anth=C₁₄ H₁₀ ^2- , thf=tetrahydrofuran) toward Brønsted acid [NEt₃ H][BPh₄ ] and azobenzene is reported. While a stepwise protonation of 2-anth-Li with two equivalents of [NEt₃ H][BPh₄ ] afforded the scandium cation [Sc{N(tBu)Xy}₂ (thf)₂ ][BPh₄ ] (3), reduction of azobenzene gave a thermolabile, anionic scandium reduced azobenzene complex [Li(thf)][Sc{N(tBu)Xy}₂ (η² -PhNNPh)] (4), which slowly lost one of the anilide ligands to form the neutral scandium azobenzene complex dimer [Sc{N(tBu)Xy}(μ-η² :η² -Ph₂ N₂ )]₂ (5). Exposure of 3 to CO₂ produced the scandium carbamate complex [Sc{κ² -O₂ CN(tBu)(Xy)}₂ ][BPh₄ ] (6) as a result of CO₂ insertion into the Sc-N bonds. In an attempt to prepare scandium hydrides, the reaction of 3 with the hydride sources LiAlH₄ and Na[BEt₃ H] led to the terminal aluminum hydride [AlH{N(tBu)Xy}₂ (thf)] (7) and the scandium n-butoxide [Sc{N(tBu)(Xy)}₂ (μ-OnBu)] (8) after Sc/Al transmetalation and nucleophilic ring-opening of THF, respectively. All reported compounds isolated in moderate to good yields were fully characterized.

SUBMITTER: Ghana P

PROVIDER: S-EPMC8596697 | biostudies-literature | 2021 Oct

REPOSITORIES: biostudies-literature

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Scandium Reduced Arene Complex: Protonation and Reaction with Azobenzene.

Ghana Priyabrata P Spaniol Thomas P TP Okuda Jun J

Chemistry, an Asian journal 20210902 20

The reactivity of the reduced anthracene complex of scandium [Li(thf)3 ][Sc{N(tBu)Xy}2 (anth)] (2-anth-Li) (Xy=3,5-Me2 C6 H3 ; anth=C14 H10 2- , thf=tetrahydrofuran) toward Brønsted acid [NEt3 H][BPh4 ] and azobenzene is reported. While a stepwise protonation of 2-anth-Li with two equivalents of [NEt3 H][BPh4 ] afforded the scandium cation [Sc{N(tBu)Xy}2 ...[more]

PMID: 34390326

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Project description:Retaining glycoside hydrolases use acid/base catalysis with an enzymatic acid/base protonating the glycosidic bond oxygen to facilitate leaving-group departure alongside attack by a catalytic nucleophile to form a covalent intermediate. Generally, this acid/base protonates the oxygen laterally with respect to the sugar ring, which places the catalytic acid/base and nucleophile carboxylates within about 4.5-6.5 Å of each other. However, in glycoside hydrolase (GH) family 116, including disease-related human acid β-glucosidase 2 (GBA2), the distance between the catalytic acid/base and the nucleophile is around 8 Å (PDB: 5BVU) and the catalytic acid/base appears to be above the plane of the pyranose ring, rather than being lateral to that plane, which could have catalytic consequences. However, no structure of an enzyme-substrate complex is available for this GH family. Here, we report the structures of Thermoanaerobacterium xylanolyticum β-glucosidase (TxGH116) D593N acid/base mutant in complexes with cellobiose and laminaribiose and its catalytic mechanism. We confirm that the amide hydrogen bonding to the glycosidic oxygen is in a perpendicular rather than lateral orientation. Quantum mechanics/molecular mechanics (QM/MM) simulations of the glycosylation half-reaction in wild-type TxGH116 indicate that the substrate binds with the nonreducing glucose residue in an unusual relaxed 4C1 chair at the -1 subsite. Nevertheless, the reaction can still proceed through a 4H3 half-chair transition state, as in classical retaining β-glucosidases, as the catalytic acid D593 protonates the perpendicular electron pair. The glucose C6OH is locked in a gauche, trans orientation with respect to the C5-O5 and C4-C5 bonds to facilitate perpendicular protonation. These data imply a unique protonation trajectory in Clan-O glycoside hydrolases, which has strong implications for the design of inhibitors specific to either lateral protonators, such as human GBA1, or perpendicular protonators, such as human GBA2.

Dataset Information

Scandium Reduced Arene Complex: Protonation and Reaction with Azobenzene.

Publications

Scandium Reduced Arene Complex: Protonation and Reaction with Azobenzene.

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