Characterization and Fate of a Septanosyl Ferrier Cation in the Gas and Solution Phases

Ferrier reactions follow a mechanistic pathway whereby Lewis acid activation of a cyclic enol ether facilitates departure of an allylic leaving group to form a glycosyl Ferrier cation. Attack on the Ferrier cation provides a new acetal linkage concurrent with the transposition of the alkene moiety. The idiosyncratic outcomes of Ferrier reactions of seven-membered ring carbohydrate-based oxepines prompted an investigation of its corresponding septanosyl Ferrier cation. Experiments that characterized the ion, including gas-phase cryogenic IR spectroscopy matched with density functional theory-calculated spectra of candidate cation structures, as well as product analysis from solution-phase Ferrier reactions, are reported here. Results from both approaches revealed an inclination of the seven-membered ring cation to contract to five-membered ring structures. Gas-phase IR spectra matched best to calculated spectra of structures in which five-membered dioxolenium formation opened the oxepine ring. In the solution phase, an attack on the ion by water led to an acyclic enal that cyclized to a C-methylene-aldehydo arabinofuranoside species. Attack by allyl trimethylsilane, on the other hand, was diastereoselective and yielded a C-allyl septanoside

Molecular Recognition of Amino Acids, Peptides, and Proteins by Cucurbit[n]uril Receptors

At the forefront of the endeavor to understand and manipulate living systems is the design and study of receptors that bind with high affinity and selectivity to specific amino acids, peptides, and proteins. Cucurbit[n]urils are among the most promising class of synthetic receptors for these targets due to their high affinities and selectivities in aqueous media and to the unique combination of electrostatic and hydrophobic interactions that govern binding. The fundamental supramolecular chemistry in this area has been explored in depth, and novel, useful applications are beginning to emerge

Students’ Perceptions of Positive School Experiences: An Investigation on the Similarities and Differences Over Time

This study aimed to understand the factors of positive school experiences from children’s own perspectives. The foundation of this research depended on school satisfaction, school connectedness, and academic self-perception. Overall, these terms encompassed general feelings about enjoying school, engaging with the rules and content, and thinking of oneself as smart. I wondered how these variables individually and cohesively contributed to positive school experiences and how these relationships changed depending on students’ ages. Based on previous literature, I predicted that students would feel less positively about their school experiences as their grade level increased. My methodology was based on interviews with students between the ages of four and ten years old. I constructed a semi-structured interview about their experiences at school and conversed with participants individually for about ten minutes each. After completing interviews, I analyzed all the responses and created six codes, or themes, based on participants’ sentiments - liking school, having time for play, socializing with peers, appreciating learning, feeling smart, and having agency. These six codes were the ultimate contributors to students’ positive school experiences. Participants were divided into three groups for analysis, and reports for students in the youngest age group were compared to responses on teacher questionnaires. After analysis, it was revealed that students in the youngest age group had the most positive school experiences. Students rated play and social factors of school as most important, independent of age. In contrast, students in the oldest age group reported the highest scores for smart and agency. Future research has been proposed to investigate differentiations of play between grade levels and the possible benefits to socioemotional development and academic achievement

Synthesis of <i>C</i>‑Septanosides from Pyranoses via Vinyl Addition and Electrophilic Cyclization

A two-step synthesis of <i>C</i>-septanosides from pyranoses is reported. Vinyl addition to tetra-<i>O</i>-benzyl d-glucose, d-galactose, and d-mannose gave the corresponding allylic alcohols. Electrophilic cyclization followed by treatment with iodine gave iodomethyl <i>C</i>-septanosides suitable for substitution reactions. The cyclizations were diastereoselective, giving <i>cis</i>-1,2 configured <i>C</i>-septanosides. Selectivity is rationalized through a model for electrophilic additions that invokes the conformation of the allylic system. This new approach should be generally applicable to the synthesis of a variety of <i>C</i>-septanosides

Positioning and Configuration of Key Atoms Influence the Topology of [13]-Macrodiolides

Key atoms at specific positions along the ring govern the shape, or “topology” of a group of [13]-macrodiolides. Here we report the synthesis of these macrocycles and their characterization by functional and structural methods. The [13]-macrodiolides are organized by three four-atom planar units that help to rigidify them and one hinge atom that enables the planar units to orient themselves. The driving force for the organization of the structures is the minimization of steric strain on groups attached to the key atoms. When the key atom is a stereocenter, a macrocycle with planar chirality is observed. An alternative cup-like topology arises when the key atom bears two alkyl groups. Additionally, the key atoms can work in a coordinated fashion to guide one topology over another. The synthesis relied on an acylation-ring closing metathesis sequence. Rigidity was demonstrated by variable-temperature NMR experiments and diastereoselective epoxidation reactions. X-ray crystal structures of representative [13]-macrodiolides served as the basis of the structural observations made. The results provide a framework for the design of new macrocycles with well-defined structures as well as for understanding some general principles that influence the topology of natural product macrocycles

Positioning and Configuration of Key Atoms Influence the Topology of [13]-Macrodiolides

Key atoms at specific positions along the ring govern the shape, or “topology” of a group of [13]-macrodiolides. Here we report the synthesis of these macrocycles and their characterization by functional and structural methods. The [13]-macrodiolides are organized by three four-atom planar units that help to rigidify them and one hinge atom that enables the planar units to orient themselves. The driving force for the organization of the structures is the minimization of steric strain on groups attached to the key atoms. When the key atom is a stereocenter, a macrocycle with planar chirality is observed. An alternative cup-like topology arises when the key atom bears two alkyl groups. Additionally, the key atoms can work in a coordinated fashion to guide one topology over another. The synthesis relied on an acylation-ring closing metathesis sequence. Rigidity was demonstrated by variable-temperature NMR experiments and diastereoselective epoxidation reactions. X-ray crystal structures of representative [13]-macrodiolides served as the basis of the structural observations made. The results provide a framework for the design of new macrocycles with well-defined structures as well as for understanding some general principles that influence the topology of natural product macrocycles

Positioning and Configuration of Key Atoms Influence the Topology of [13]-Macrodiolides

Key atoms at specific positions along the ring govern the shape, or “topology” of a group of [13]-macrodiolides. Here we report the synthesis of these macrocycles and their characterization by functional and structural methods. The [13]-macrodiolides are organized by three four-atom planar units that help to rigidify them and one hinge atom that enables the planar units to orient themselves. The driving force for the organization of the structures is the minimization of steric strain on groups attached to the key atoms. When the key atom is a stereocenter, a macrocycle with planar chirality is observed. An alternative cup-like topology arises when the key atom bears two alkyl groups. Additionally, the key atoms can work in a coordinated fashion to guide one topology over another. The synthesis relied on an acylation-ring closing metathesis sequence. Rigidity was demonstrated by variable-temperature NMR experiments and diastereoselective epoxidation reactions. X-ray crystal structures of representative [13]-macrodiolides served as the basis of the structural observations made. The results provide a framework for the design of new macrocycles with well-defined structures as well as for understanding some general principles that influence the topology of natural product macrocycles