Transamidation-driven molecular pumps Lorna Binks 1 , Chong Tian 1 , Stephen D. P. Fielden 1 , Iñigo J. Vitorica-Yrezabal 1 and David A. Leigh 1,2 1 University of Manchester, UK, 2 East China Normal University, China Protein pumps actively transport substrates away from equilibrium. 1 These biomolecular machines are generally extremely structurally complex, assembled from multiple protein subunits and having molecular masses in excess of 500 kDa. A number of much smaller artificial molecular pumps have been designed. 2 These minimalist systems can provide insights into the basic mechanisms required to drive chemical systems away from equilibrium 3 .Here we report a new class of synthetic molecular pumps that use a stepwise information ratchet mechanism to achieve the kinetic gating required to sequester their macrocyclic substrates from bulk solution. 1 Threading occurs as a result of active template reactions between the pump terminus amine and an acyl electrophile, whereby the bond-forming reaction is accelerated through the cavity of a crown ether. 2 Carboxylation of the resulting amide results in displacement of the ring to the collection region of the thread. Conversion of the carbamate to a phenolic ester provides an intermediate rotaxane suitable for further pumping cycles. In this way rings can be ratcheted onto a thread from one or both ends of appropriately designed molecular pumps. Each pumping cycle results in one additional ring being added to the thread per terminus acyl group. The absence of pseudorotaxane states ensures that no dethreading of intermediates occurs during the pump operation. This facilitates the loading of different macrocycles in any chosen sequence, illustrated by the pump-mediated synthesis of a [4]rotaxane containing three different macrocycles as a single sequence isomer. A [5]rotaxane synthesized using a dual- opening transamidation pump was structurally characterized by single-crystal X-ray diffraction, revealing a series of stabilizing CH···O interactions between the crown ethers and the polyethylene glycol catchment region of the thread.The ability to drive molecular systems directionally away from equilibrium with ratchet mechanisms has ramifications not only for synthesis but for many other aspects of molecular nanotechnology. 6
References 1. J. C. Skou, Angew. Chem., Int. Ed. ,1998, 37 , 2320−2328. 2. S. Erbas-Cakmak, D. A. Leigh, C. T. McTernan, A. L. Nussbaumer, Chem. Rev. , 2015, 115 ,10081−10206. 3. E. R. Kay, D. A. Leigh, F. Zerbetto, Angew. Chem., Int. Ed. , 2007, 46 , 72−191. 4. L.Binks, C. Tian, S. D. P. Fielden, I. J. Vitorica-Yrezabal and D. A. Leigh, J. Am. Chem. Soc. , 2022, 144 , 15838-15844. 5. S.D. P. Fielden, D. A. Leigh, C. T. Mcternan, B. Perez-Saavedra, I. J. Vitorica-Yrezabal, J. Am. Chem. Soc. ,2018, 140 , 6049−6052. 6. I. Aprahamian, ACS Cent.Sci. , 2020, 6 , 347−358.
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