Cucurbit[7]uril Host-Guest Complexes With Drug Molecules Containing Isoquinoline Groups

Thumbnail Image
Kwok, Julian
isoquinoline , Cucurbit[7]uril
This thesis describes the host-guest chemistry between cucurbit[7]uril (CB[7]) and various guests that contain isoquinoline groups, including tacrine, papaverine, N-methyl papaverinium, N-methyl laudanosinium, 6,7-dimethoxy-1,2,3,4,-tetrahydroisoquinoline, N, N-dimethyl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolinium, α,α'-bis(isoquinolinium)-p-xylene and a series of 1,n-bis(isoquinolinium) alkane dications (Isq(CH2)nIsq2+, where n = 2, 4-6, 8-10 and 12). The stoichiometries and strengths of the host-guest interactions were studied using UV-visible and 1H NMR spectroscopy and high-resolution electrospray ionization mass spectrometry. A focus of this thesis is an investigation of the effects of varying the chemical structure within a series of isoquinoline-based guest on the strength of the binding affinity . The 1H NMR spectra indicates that CB[7] prefers the saturated ring of tacrine as opposed to the aromatic ring, resulting in a binding constant of (2.7 ± 0.25) x 104 M-1. The N-methylations of papaverine and 6,7-dimethoxy-1,2,3,4,-tetrahydroisoquinoline increased their respective binding constants from those of the protonated forms and changed the nature of the interaction of the guest with CB[7]. . With the series of 1,n-bis(isoquinolinium)-alkane dications, the mode of binding to CB[7] depends on the number of carbons in the polymethylene chain that bridges the two isoquinolinium groups. When the bridge is less than six carbons, CB[7] binds sequentially on the isoquinolinium groups to form 1:1 and 2:1 host-guest complexes. If the polymethylene chain length is between six and ten carbons, or is replaced with a p-xylyl group, the first CB[7] will bind over the central bridge, resulting in both of the polar portals forming ion-dipole interactions with both positively charged nitrogens. A second CB[7] binds to a terminal isoquinolinium group, which forces the original bound CB[7] to relocate to the other isoquinolinium group. When the polymethylene bridges contains twelve carbons, two CB[7] binds sequentially to the isoquinolinium groups, as observed with the shortest polymethylene bridges. With this series of guest, the binding constant is the largest when the bridge is two carbons long. This is due to the two isoquinolinium groups being in close proximity to each other, allowing CB[7] to interact with both nitrogens while still binding around the isoquinoline group.
External DOI