Significant Inter- and Intramolecular O−H···FC Hydrogen Bonding

Barbarich, Thomas J.; Rithner, Christopher D.; Miller, Susie M.; Anderson, Oren P.; Strauss, Steven H.

doi:10.1021/ja983552e

Cited by 125 publications

(86 citation statements)

References 23 publications

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“…Evidence against, [28] and in favor of such interactions has been described. [29] In the present case, the structure-selectivity relationship revealed by catalysts 5, 9, and 11 may suggest that a continuum exists with these catalysts (Scheme 8) that is consistent with a moderate, but attractive CF···HN interaction in the dominant transition state.…”

Section: H Nmr At 100 8c ([D 6 ]Dmso)supporting

confidence: 55%

Functional Analysis of an Aspartate‐Based Epoxidation Catalyst with Amide‐to‐Alkene Peptidomimetic Catalyst Analogues

2008

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Keywordsepoxidation; peptide; asymmetric catalysis; olefin isostere; fluorine; peptidomimetic The biosynthesis of natural products that contain epoxides represents a powerful stimulus for the study of "epoxidase" enzymes. [i] Likewise, these processes have inspired a generation of science focused on small molecule catalysts that mediate selective epoxidations through a variety of mechanisms. [ii] With respect to the naturally occurring epoxidases, the mechanistic basis of O-atom transfer is often associated with the chemistry of either flavinoid cofactors, P450 enzymes containing a heme group, or chloroperoxidases that lead to stepwise ring formation. [iii] In thinking about the known biosynthetic apparatus for epoxide formation, we became curious about an alternative mode for O-atom transferone based on functional groups available in proteins, but perhaps not well-documented in the biosynthesis of epoxides. In particular, we speculated and recently showed that asparticacid-containing peptides (e.g., 1; Figure 1a) might shuttle between the side-chain carboxylic acid and the corresponding peracid (e.g., 2) creating a catalytic cycle competent for asymmetric epoxidation with turnover of the aspartate-derived catalyst. Such an approach is orthogonal to the Julia-Colonna epoxidation, a complementary peptide-based epoxidation based on a nucleophilic mechanism. [iv] Indeed, as shown in Figure 1b, this new electrophilic epoxidation catalytic cycle mediates the asymmetric epoxidation of substrates like 3 to give products like 4 with up to 92% ee. [v] Mechanistic questions abound in this catalytic system. To date, we have identified a number of relevant aspects. For example, we observed off-catalytic cycle intermediates, including catalytically inactive diacyl peroxides (6). [vi] We also showed that these off-cycle intermediates could be reinserted into the productive pathway through the action of nucleophiles such as DMAP or DMAP-N-oxide (7). On the other hand, the basis of stereochemical information transfer was not immediately clear. Indeed, the high precision delineation of the stereochemical mode of action of chiral catalysts is a critical frontier in the discipline of asymmetric catalysis, whether the catalysts are enzymes or small molecules. With this back-drop, we began a detailed study of the mode of action for catalyst 5.The conversion of 3 to 4 was originally undertaken with the hypothesis that substratecatalyst hydrogen bonding might contribute to transition state organization. [vii] Indeed, a substrate lacking obvious H-bonding capability (phenylcyclohexene) was found to undergo epoxidation with catalyst 5 with low enantioselectivity (~10% ee). Thus, we envisioned several potential loci for contacts between 3 and 5 (Figure 2a). Shown in blue is the site that

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Section: H Nmr At 100 8c ([D 6 ]Dmso)supporting

confidence: 55%

Functional Analysis of an Aspartate‐Based Epoxidation Catalyst with Amide‐to‐Alkene Peptidomimetic Catalyst Analogues

2008

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“…[9a] In contrast to previously reported J HF ), [42] and 2) the available crystal structures of Ti and Zr derivatives show that close M···FÀC contacts are absent. Although long-range C À H···F À C coupling in fluorinated organic molecules has been investigated for several decades, [43] literature reports of fluorinated organometallic complexes that exhibit intramolecular 1 H- 19 F coupling are sparse. [44] Van Eldik, Goldberg and co-workers [45] suggested the presence of CÀH···FÀC interactions (analogous to Scheme 2 A, like 1 and 4), which were observed in an X-ray crystal structure, to account for 1 H- 19 F and 13 C-19 F coupling between the three methyl ligands and six CF 3 substituents in Tp…”

Section: Resultsmentioning

confidence: 99%

Scalar Coupling Across [CH⋅⋅⋅FC] Interactions in (σ‐Aryl)‐Chelating Post‐Metallocenes

Liu

Chan

et al. 2011

Chemistry A European J

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The nature and importance of C-H···F-C interactions is a topical yet controversial issue, and the development of spectroscopic methods to probe such contacts is therefore warranted. A series of Group 4 bis(benzyl) complexes supported by (σ-aryl)-2-phenolate-6-pyridyl [O,C,N-R(1)] ligands bearing a fluorinated R(1) group (CF(3) or F) in the vicinity of the metal has been prepared. The X-ray crystal structure of the CF(3)-substituted Hf derivative features intramolecular C-H···F-C and Hf···F-C contacts. All complexes have been characterized by multinuclear NMR spectroscopy. The (1)H and (13)C NMR spectra of [M(O,C,N-CF(3))(CH(2)Ph)(2)] derivatives display coupling (assigned to (1h)J(HF) and (2h)J(CF) for Ti; (3)J(HF) and (2)J(CF) (through M···F) for Hf and Zr) between the benzyl CH(2) and CF(3) moieties. [(1)H,(19)F]-HMBC NMR experiments have been performed for the M-[O,C,N-R(1)] complexes and their [O,N,C] counterparts, revealing significant scalar coupling across the C-H···F-C interactions for Ti-[O,C,N] and [O,N,C] species.

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“…The large dipole moment is the most likely culprit for stabilizing the interdigitated phase by reducing the unfavorable exposure of the hydrophobic acyl chains to water. However, the slightly larger van der Waals radius and the possibility of weak hydrogen bonding may also play a role [73][74][75][76][77]. …”

Section: The Monofluorinated Analogue Of Dppc: F-dppcmentioning

confidence: 99%

Differential Scanning Calorimetry Studies of Phospholipid Membranes: The Interdigitated Gel Phase

Smith¹,

Dea²

2013

Applications of Calorimetry in a Wide Context - Differential Scanning Calorimetry, Isothermal Titration Calorimetry and Microca

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Significant Inter- and Intramolecular O−H···FC Hydrogen Bonding

Cited by 125 publications

References 23 publications

Functional Analysis of an Aspartate‐Based Epoxidation Catalyst with Amide‐to‐Alkene Peptidomimetic Catalyst Analogues

Functional Analysis of an Aspartate‐Based Epoxidation Catalyst with Amide‐to‐Alkene Peptidomimetic Catalyst Analogues

Scalar Coupling Across [CH⋅⋅⋅FC] Interactions in (σ‐Aryl)‐Chelating Post‐Metallocenes

Differential Scanning Calorimetry Studies of Phospholipid Membranes: The Interdigitated Gel Phase

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