Skip to Main Content
 

Global Search Box

 
 
 
 

ETD Abstract Container

Abstract Header

The Folding and Assembly of Stereoisomeric Twisted Baskets

Pratumyot, Yaowalak

Abstract Details

2016, Doctor of Philosophy, Ohio State University, Chemistry.
The chirality of organic building blocks is of great importance for creating a variety of useful materials and drugs. The production of enantio-enriched molecules thus constitutes an integral part of many organic processes. Cavitands are concave organic compounds that can be used for trapping smaller guest molecules. While chiral cavitands exist, there still remains a need to design and develop hosts that are complementary in size and shape to numerous chiral guests for their detection, resolution and/or facile conversion into other useful compounds. Examples of such chiral molecules, and of interest to this work, include many pharmaceuticals, commodity chemicals and chemical warfare agents. In line with a need for developing novel chiral hosts, we recently described a synthetic method for the preparation of cup-shaped cavitands possessing a nonfunctional hydrocarbon framework and a twisted (chiral) inner space. In particular, a tandem of cycloalkylation reactions was promoted with strong acids to, via general-acid catalysis, give rise to baskets (akin to (P/M)-1syn, Figure 1.23) comprising six stereogenic centers of the same kind (R or S) embedded in the host's bicyclic platform. In this study, we expanded the scope of our preliminary investigation by: (a) optimizing a procedure for obtaining functionalized and twisted baskets with either right-(P)-1syn or left-handed (M)-1syn sense of twist (Figure 1.23) and (b) resolving such racemic host into pure enantiomers. These modular and easily accessible cavitands are C3 symmetric, possessing: (a) six esters at the rim for additional functionalization, (b) unique chiroptical characteristics, (c) photochemically sensitizing sidewalls for promoting photochirogenesis and (d) deep and twisted inner space for discriminating chiral guests. Upon obtaining enantiopure twisted basket (P)-1 or (M)-1, we modified the rim of the baskets to obtain gated baskets of type (P)-13, (S3, M)-15, and (P)-17. Basket (P)-13 possesses three quinoline gates tethered to the twisted platform via CH2 hinges. This chiral cavitand was found to fold quinoline gates at the rim of its twisted platform in acetonitrile and give molecular capsules that assemble into large unilamellar vesicles. In less polar dichloromethane, cup-shaped (P)-13 packed into vesicles as well, although with the quinoline gates unfolded. The orientation of quinoline gates in folded (P)-13 in acetonitrile was found to be in both clockwise (+) and counterclockwise (–) directions, denoting the absence of chirality transfer from the chiral platform to the gates. In order to produce a twisted basket with unidirectionally folded gates, we introduced an S stereogenic center to each hinge position, generating (S3, M)-15. In line with our previous study,1 we found that such CH(CH3) stereogenic center with S configuration in (S3, M)-15 directed the twisting of its quinoline gates at the rim in a counterclockwise orientation (–). The coordination of (S3, M)-15 to Cu(II) was found to give 1:1 stoichiometric complex. The coordination of quinoline nitrogens to Cu(II) in the center above the basket cavity drives the conformational equilibrium of (S3, M)-15 in acetonitrile toward a folded structure, with quinoline gates oriented in counterclockwise (–) fashion. Gated basket (P)-17/(M)-17 contains three amidopyridine gates at the rim. With racemic (P/M)-17, it was found that this host (1H NMR and IR spectroscopy) stayed monomeric in CDCl3 at 298.0 K with the gates forming a seam of intramolecular N–H···N hydrogen bonds. In particular, the amidopyridine gates assume a unidirectional orientation, as directed by the twisted platform, to either clockwise (+) or counterclockwise (–) orientation of intramolecular N–H···N hydrogen bonds. The results of computational studies suggested a small energy difference (¿Ep = 1.07 kcal/mol) content between (P)-17(+) and (P)-17(–), with (P)-17(–) possessing less energy. The experimental results with eanatiopure (P)-17 (Circular Dichroism) suggested that the P-shaped cup sets the amidopyridine gates in a clockwise (+) orientation of intramolecular N–H···N hydrogen bonds. The folded form of spacious (355 Å3) and chiral (P/M)-17 undergoes an unfolding process in the presence of the polar [D6]DMSO or CF3CH2OH solvent; specifically, with around 25 vol.-% of these solvents, the N–H···N hydrogen bonds at the rim are broken, thereby allowing a stochastic rotation of the amidopyridine gates about the rim. Interestingly, the thermal stability of folded (P/M)-17 is good with only a small fraction of unfolded state(s) forming at 104 °C in o-xylene.
Jovica Badjic (Advisor)
Jon Parquette (Committee Member)
Psaras McGrier (Committee Member)
Shili Lin (Committee Member)
195 p.

Recommended Citations

Citations

  • Pratumyot, Y. (2016). The Folding and Assembly of Stereoisomeric Twisted Baskets [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1471602282

    APA Style (7th edition)

  • Pratumyot, Yaowalak. The Folding and Assembly of Stereoisomeric Twisted Baskets . 2016. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1471602282.

    MLA Style (8th edition)

  • Pratumyot, Yaowalak. "The Folding and Assembly of Stereoisomeric Twisted Baskets ." Doctoral dissertation, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1471602282

    Chicago Manual of Style (17th edition)