Enantioselective Sulfonimidamide Acylation via a Cinchona Alkaloid-Catalyzed Desymmetrization: Scope, Data Science, and Mechanistic Investigation

Methods to access chiral sulfur(VI) pharmacophores are of interest in medicinal and synthetic chemistry. We report the desymmetrization of unprotected sulfonimidamides via asymmetric acylation with a cinchona-phosphinate catalyst. The desired products are formed in excellent yield and enantioselectivity with no observed bis-acylation. A data-science-driven approach to substrate scope evaluation was coupled to high throughput experimentation (HTE) to facilitate statistical modeling in order to inform mechanistic studies. Reaction kinetics, catalyst structural studies, and density functional theory (DFT) transition state analysis elucidated the turnover-limiting step to be the collapse of the tetrahedral intermediate and provided key insights into the catalyst-substrate structure-activity relationships responsible for the origin of the enantioselectivity. This study offers a reliable method for accessing enantioenriched sulfonimidamides to propel their application as pharmacophores and serves as an example of the mechanistic insight that can be gleaned from integrating data science and traditional physical organic techniques.

Enhancement of awareness through feedback does not lead to interlimb transfer of obstacle crossing in virtual reality

Locomotor skill transfer is an essential feature of motor adaptation and represents the generalization of learned skills. We previously showed that gait adaptation after crossing virtual obstacles did not transfer to the untrained limb and suggested it may be due to missing feedback of performance. This study investigated whether providing feedback and an explicit goal during training would lead to transfer of adaptive skills to the untrained limb. Thirteen young adults crossed 50 virtual obstacles with one (trained) leg. Subsequently, they performed 50 trials with their other (transfer) leg upon notice about the side change. Visual feedback about crossing performance (toe clearance) was provided using a color scale. In addition, joint angles of the ankle, knee, and hip were calculated for the crossing legs. Toe clearance decreased with repeated obstacle crossing from 7.8 ± 2.7 cm to 4.6 ± 1.7 cm for the trained leg and from 6.8 ± 3.0 cm to 4.4 ± 2.0 cm (p < 0.05) for the transfer leg with similar adaptation rates between limbs. Toe clearance was significantly higher for the first trials of the transfer leg compared to the last trials of the training leg (p < 0.05). Furthermore, statistical parametric mapping revealed similar joint kinematics for trained and transfer legs in the initial training trials but differed in knee and hip joints when comparing the last trials of the trained leg with the first trials of the transfer leg. We concluded that locomotor skills acquired during a virtual obstacle crossing task are limb-specific and that enhanced awareness does not seem to improve interlimb transfer.

Exploring Structure-Function Relationships of Aryl Pyrrolidine-Based Hydrogen-Bond Donors in Asymmetric Catalysis Using Data-Driven Techniques

Hydrogen bond-based organocatalysts rely on networks of attractive noncovalent interactions (NCIs) to impart enantioselectivity. As a specific example, aryl pyrrolidine substituted urea, thiourea, and squaramide organocatalysts function cooperatively through hydrogen bonding and difficult-to-predict NCIs as a function of the reaction partners. To uncover the synergistic effect of the structural components of this catalyst class, we applied data science tools to study various model reactions using a derivatized, aryl pyrrolidine-based, hydrogen-bond donor (HBD) catalyst library. Through a combination of experimentally collected data and data mined from previous reports, statistical models were constructed, illuminating the general features necessary for high enantioselectivity. A distinct dependence on the identity of the electrophilic reaction partner and HBD catalyst is observed, suggesting that a general interaction is conserved throughout the reactions analyzed. The resulting models also demonstrate predictive capability by the successful improvement of a previously reported reaction using out-of-sample reaction components. Overall, this study highlights the power of data science in exploring mechanistic hypotheses in asymmetric HBD catalysis and provides a prediction platform applicable in future reaction optimization.

Catalytic asymmetric C-H insertion reactions of vinyl carbocations

From the preparation of pharmaceuticals to enzymatic construction of natural products, carbocations are central to molecular synthesis. Although these reactive intermediates are engaged in stereoselective processes in nature, exerting enantiocontrol over carbocations with synthetic catalysts remains challenging. Many resonance-stabilized tricoordinated carbocations, such as iminium and oxocarbenium ions, have been applied in catalytic enantioselective reactions. However, their dicoordinated counterparts (aryl and vinyl carbocations) have not, despite their emerging utility in chemical synthesis. We report the discovery of a highly enantioselective vinyl carbocation carbon-hydrogen (C-H) insertion reaction enabled by imidodiphosphorimidate organocatalysts. Active site confinement featured in this catalyst class not only enables effective enantiocontrol but also expands the scope of vinyl cation C-H insertion chemistry, which broadens the utility of this transition metal-free C(sp³)-H functionalization platform.

Noncovalent Stabilization of Radical Intermediates in the Enantioselective Hydroamination of Alkenes with Sulfonamides

Noncovalent interactions (NCIs) are critical elements of molecular recognition in a wide variety of chemical contexts. While NCIs have been studied extensively for closed-shell molecules and ions, very little is understood about the structures and properties of NCIs involving free radical intermediates. In this report, we describe a detailed mechanistic study of the enantioselective radical hydroamination of alkenes with sulfonamides and present evidence suggesting that the basis for asymmetric induction in this process arises from attractive NCIs between a neutral sulfonamidyl radical intermediate and a chiral phosphoric acid (CPA). We describe experimental, computational, and data science-based evidence that identifies the specific radical NCIs that form the basis for the enantioselectivity. Kinetic studies support that C-N bond formation determines the enantioselectivity. Density functional theory investigations revealed the importance of both strong H-bonding between the CPA and the N-centered radical and a network of aryl-based NCIs that serve to stabilize the favored diastereomeric transition state. The contributions of these specific aryl-based NCIs to the selectivity were further confirmed through multivariate linear regression analysis by comparing the measured enantioselectivity to computed descriptors. These results highlight the power of NCIs to enable high levels of enantioselectivity in reactions involving uncharged open-shell intermediates and expand our understanding of radical-molecule interactions.

Stability recovery performance in adults over a wide age range: A multicentre reliability analysis using different lean-and-release test protocols

The ability to effectively increase the base of support is crucial to prevent from falling due to stability disturbances and has been commonly assessed using the forward-directed lean-and-release test. With this multicentre study we examined whether the assessment of stability recovery performance using two different forward lean-and-release test protocols is reliable in adults over a wide age range. Ninety-seven healthy adults (age from 21 to 80 years) were randomly assigned to one out of two lean angle protocols: gradual increase to maximal forward-lean angle (maximal lean angle; n = 43; seven participants were excluded due to marker artefacts) or predefined lean angle (single lean angle; n = 26; 21 participants needed to be excluded due to multiple stepping after release or marker artefacts). Both protocols were repeated after 0.5 h and 48 h to investigate intra- and inter-session reliability. Stability recovery performance was examined using the margin of stability at release (MoS_RL) and touchdown (MoS_TD) and increase in base of support (BoS_TD). Intraclass correlation coefficients (confidence intervals at 95%) for the maximal lean angle and for the single lean angle were respectively 0.93 (0.89-0.96) and 0.94 (0.89-0.97) in MoS_RL, 0.85 (0.77-0.91) and 0.67 (0.48-0.82) in MoS_TD and 0.88 (0.81-0.93) and 0.80 (0.66-0.90) in BoS_TD, with equivalence being revealed for each parameter between all three measurements (p < 0.01). We concluded that the assessment of stability recovery performance parameters in adults over a wide age range with the means of the forward lean-and-release test is reliable, independent of the used lean angle protocol.

Linear Regression Model Development for Analysis of Asymmetric Copper-Bisoxazoline Catalysis

Multivariate linear regression analysis (MLR) is used to unify and correlate different categories of asymmetric Cu-bisoxazoline (BOX) catalysis. The versatility of Cu-BOX complexes has been leveraged for several types of enantioselective transformations including cyclopropanation, Diels-Alder cycloadditions and difunctionalization of alkenes. Statistical tools and extensive molecular featurization has guided the development of an inclusive linear regression model, providing a predictive platform and readily interpretable descriptors. Mechanism-specific categorization of curated datasets and parameterization of reaction components allows for simultaneous analysis of disparate organometallic intermediates such as carbenes and Lewis acid adducts, all unified by a common ligand scaffold and metal ion. Additionally, this workflow permitted the development of a complementary linear regression model correlating analogous BOX-catalyzed reactions employing Ni, Fe, Mg, and Pd complexes. Comparison of ligand parameters in each model reveals the relevant structural requirements necessary for high selectivity. Overall, this strategy highlights the utility of MLR analysis in exploring mechanistically driven correlations across a diverse chemical space in organometallic chemistry and presents an applicable workflow for related ligand classes.

Evidence that ageing does not influence the uniformity of the muscle-tendon unit adaptation in master sprinters

Differences in the adaptation processes between muscle and tendon in response to mechanical loading can lead to non-uniform mechanical properties within the muscle-tendon unit (MTU), potentially increasing injury risk. The current study analysed the mechanical properties of the triceps surae (TS) MTU in 10 young (YS; 22 ± 3 yrs) and 10 older (OS; age 65 ± 8 yrs; i.e. master) (inter)national level sprinters and 11 young recreationally active adults (YC; 23 ± 3 yrs) to detect possible non-uniformities in muscle and tendon adaptation due to habitual mechanical loading and ageing. Triceps surae muscle strength, tendon stiffness and maximal tendon strain were assessed in both legs during maximal voluntary isometric plantarflexion contractions via dynamometry and ultrasonography. Irrespective of the leg, OS and YC in comparison to YS demonstrated significantly (P < 0.05) lower TS muscle strength and tendon stiffness, with no differences between OS and YC. Furthermore, no group differences were detected in the maximal tendon strain (average of both legs: OS 3.7 ± 0.8%, YC 4.4 ± 0.8% and YS 4.3 ± 0.9%) as well as in the inter-limb symmetry indexes in muscle strength, tendon stiffness and maximal tendon strain (range across groups: -5.8 to 4.9%; negative value reflects higher value for the non-preferred leg). Thus, the findings provide no clear evidence for a disruption in the TS MTU uniformity in master sprinters, demonstrating that ageing tendons can maintain their integrity to meet the increased functional demand due to elite sports.

Obstacle avoidance training in virtual environments leads to limb-specific locomotor adaptations but not to interlimb transfer in healthy young adults

Obstacle avoidance is one of the skills required in coping with challenging situations encountered during walking. This study examined adaptation in gait stability and its interlimb transfer in a virtual obstacle avoidance task. Twelve young adults walked on a treadmill while wearing a virtual reality headset with their body state represented in the virtual environment. At random times, but always at foot touchdown, 50 virtual obstacles of constant size appeared 0.8 m in front of the participant requiring a step over with the right leg. Early, mid and late adaptation phases were investigated by pooling data from trials 1-3, 24-26 and 48-50. One left-leg obstacle appearing after 50 right-leg trials was used to investigate interlimb transfer. Toe clearance and the anteroposterior margin of stability (MoS) at foot touchdown were calculated for the stepping leg. Toe clearance decreased over repeated practice between early and late phases from 0.13 ± 0.05 m to 0.09 ± 0.04 m (mean ± SD, p < 0.05). MoS increased from 0.05 ± 0.02 m to 0.08 ± 0.02 m (p < 0.05) between early and late phases, with no significant differences between mid and late phases. No differences were found in toe clearance and MoS between the practiced right leg for early phase and the single trial of the left leg. Obstacle avoidance during walking in a virtual environment stimulated adaptive gait improvements that were related in a nonlinear manner to practice dose, though such gait adaptations seemed to be limited in their transferability between limbs.

Connecting and Analyzing Enantioselective Bifunctional Hydrogen Bond Donor Catalysis Using Data Science Tools

The generalization of related asymmetric processes in organocatalyzed reactions is an ongoing challenge due to subtle, noncovalent interactions that drive selectivity. The lack of transferability is often met with a largely empirical approach to optimizing catalyst structure and reaction conditions. This has led to the development of diverse structural catalyst motifs and inspired unique design principles in this field. Bifunctional hydrogen bond donor (HBD) catalysis exemplifies this in which a broad collection of enantioselective transformations has been successfully developed. Herein, we describe the use of data science methods to connect catalyst and substrate structural features of an array of reported enantioselective bifunctional HBD catalysis through an iterative statistical modeling process. The computational parameters used to build the correlations are mechanism-specific based on the proposed transition states, which allows for analysis into the noncovalent interactions responsible for asymmetric induction. The resulting statistical models also allow for extrapolation to out-of-sample examples to provide a prediction platform that can be used for future applications of bifunctional hydrogen bond donor catalysis. Finally, this multireaction workflow presents an opportunity to build statistical models unifying various modes of activation relevant to asymmetric organocatalysis.

Cobalt Catalyzed Reductive Spirocyclopropanation Reactions

Cobalt pyridine-diimine (PDI) complexes catalyze the reductive spirocyclopropanation of terminal 1,3-dienes. gem-Dichlorocycloalkanes serve as carbene precursors and Zn is used as a terminal electron source. The reaction is effective for a range of gem-dichloro partners including those containing sulfur and nitrogen heterocycles. An example of an intramolecular Rh-catalyzed [5 + 2]-cycloaddition of a vinyl spirocyclopropane is demonstrated, providing rapid access to a complex tricyclic framework. Overall, this catalyst system is capable of suppressing the kinetically facile 1,2-hydride shift, which has hampered the development of Simmons-Smith reactions using Zn carbenoids possessing β-hydrogen atoms.

Cobalt-Catalyzed Reductive Dimethylcyclopropanation of 1,3-Dienes

Dimethylcyclopropanes are valuable synthetic targets that are challenging to access in high yield using Zn carbenoid reagents. Herein, we describe a cobalt-catalyzed variant of the Simmons-Smith reaction that enables the efficient dimethylcyclopropanation of 1,3-dienes using a Me₂ CCl₂ /Zn reagent mixture. The reactions proceed with high regioselectivity based on the substitution pattern of the 1,3-diene. The products are vinylcyclopropanes, which serve as substrates for transition-metal-catalyzed ring-opening reactions, including 1,3-rearrangement and [5+2] cycloaddition. Preliminary studies indicate that moderately activated monoalkenes are also amenable to dimethylcyclopropanation under the conditions of cobalt catalysis.

Regioselective Simmons-Smith-type cyclopropanations of polyalkenes enabled by transition metal catalysis

A [ ^i-PrPDI]CoBr₂ complex (PDI = pyridine-diimine) catalyzes Simmons-Smith-type reductive cyclopropanation reactions using CH₂Br₂ in combination with Zn. In contrast to its non-catalytic variant, the cobalt-catalyzed cyclopropanation is capable of discriminating between alkenes of similar electronic properties based on their substitution patterns: monosubstituted > 1,1-disubstituted > (Z)-1,2-disubstituted > (E)-1,2-disubstituted > trisubstituted. This property enables synthetically useful yields to be achieved for the monocyclopropanation of polyalkene substrates, including terpene derivatives and conjugated 1,3-dienes. Mechanistic studies implicate a carbenoid species containing both Co and Zn as the catalytically relevant methylene transfer agent.

Personality disorder traits: prevalence and effects on health status in primary care patients

OBJECTIVE

Previous work in an academic setting has found that scoring in the higher ranges for selected personality disorders on an objective assessment tool was associated with increases in psychiatric co-morbidities, decreased satisfaction with health care, and diminished health related functional status. This study examines how often patients in primary care practices exhibit traits consistent with these selected disorders and what impact this has on their health related functional status and use of health care resources.

METHODS

Thirteen family practices agreed to distribute questionnaires to 50 consecutive patients in the spring of 1997. Questionnaires contained instruments that assess risk for personality disorders, health related functional status, health resource use, demographics, and depression. The relationships between four specific personality disorders (borderline, dependent, schizoid and schizotypal) and other assessed variables were explored.

RESULTS

Of the 250 patients returning completed survey instruments, 80 (32%) scored in the high range for traits consistent with one of the four target personality disorders. Patients in the high risk group also were noted to have more outpatient, emergency, and inpatient visits in the previous six months. Those in the high risk group also had significantly lower scores on seven of eight measures of health related functional status.

CONCLUSIONS

Patients who have several traits for borderline, dependent, schizoid, and schizotypal personality disorders are common in primary care practices. These patients utilize services at higher rates than others and are more likely to screen in the positive range for depressive symptoms and have overall lower health related functional status.

Enzymatic reduction of protein-bound methionine sulfoxide

An enzyme that catalyzes the reduction of methionine sulfoxide residues in ribosomal protein L12 has been partially purified from Escherichia coli extracts. Methionine sulfoxide present in oxidize [Met]enkephalin is also reduced by the purified enzyme. The enzyme is different from a previously reported E. coli enzyme that catalyzes the reduction of methionine sulfoxide to methionine [Ejiri, S. I., Weissbach, H. & Brot, N. (1980) Anal. Biochem. 102, 393--398]. Extracts of rat tissues, Euglena gracilis, Tetrahymena pyriformis, HeLa cells, and spinach also can catalyze the reduction of methionine sulfoxide residues in protein.

Eighth nerve lipoma. Case report

A case of lipoma of the right eighth cranial nerve in the cerebellopontine angle (CPA) is presented. The patient had a clinical, diagnostic, surgical, and postoperative course similar to that of patients with other small CPA tumors. The literature on this rare CPA tumor is reviewed and discussed.