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Formation and Trapping of the Thermodynamically Unfavoured Inverted-Hemicucurbit[6]uril

preprint
submitted on 10.04.2019 and posted on 11.04.2019 by Elena Prigorchenko, Sandra Kaabel, Triin Narva, Anastassia Baškir, Maria Fomitšenko, Jasper Adamson, Ivar Järving, Kari Rissanen, Toomas Tamm, Riina Aav
Amplification of a thermodynamically unfavoured macrocyclic product through the directed shift of the equilibrium between dynamic covalent chemistry library members is difficult to achieve. We show for the first time that during condensation of formaldehyde and cis-N,N'-cyclohexa-1,2-diylurea formation of inverted-cis-cyclohexanohemicucurbit[6]uril (i-cis-cycHC[6]) can be induced at the expense of thermodynamically favoured cis-cyclohexanohemicucurbit[6]uril (cis-cycHC[6]). The formation of i-cis-cycHC[6] is enhanced in low concentration of the templating chloride anion and suppressed in excess of this template. We found that reaction selectivity is governed by the solution-based template-aided dynamic combinatorial chemistry and continuous removal of the formed cycHC[6] macrocycles from the equilibrating solution by precipitation. Notably, the i-cis-cycHC[6] was isolated with 33% yield. Different binding affinities of three diastereomeric i-cis-, cis-cycHC[6] and their chiral isomer (R,R)-cycHC[6] for trifluoroacetic acid demonstrate the influence of macrocycle geometry on complex formation.

Funding

Estonian MER through Grants IUT19-9, IUT23-7, PUT692, PUT1683, PRG399

ERDF through the CoE 3.2.0101.08-0017, CoE 2014-2020.4.01.15-0013 and CoE TK134

H2020-FETOPEN, 828779, INITIO

History

Email Address of Submitting Author

riina.aav@taltech.ee

Institution

Tallinn University of Technology

Country

Estonia

ORCID For Submitting Author

0000-0001-6571-7596

Declaration of Conflict of Interest

No conflict of interest.

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