Iterative Synthesis of Stereo- and Sequence-Defined Polymers via Acid-Orthogonal Deprotection Chemistry

Absolute control over polymer stereo- and sequence structure is highly challenging in polymer chemistry. Here, an acid-orthogonal deprotection strategy is proposed for the iterative synthesis of a family of unimolecular polymers starting with enantiopure serines, featuring precise sequence, stereoconfiguration and side-chain functionalities that cannot be achieved using traditional polymerization techniques. Acid-orthogonal deprotections proceed independently of one another by the selection of protecting groups that feature the respective acid-lability. Under p-toluenesulfonic acid, acidolysis of tert-butyloxycarbonyl can proceed exclusively, while low-dosage trifluoroacetic acid and low temperature only trigger the selective and quantitative cleavage of trityl. The pioneering use of this acid-orthogonal deprotection chemistry increases the compatibility with otherwise sensitive groups and opens up pathways to facilely introduce structural and functional diversity into stereo- and sequence-defined polymers, thus imparting their unique properties beyond natural biopolymers.

Design and Hybridization Properties of Acyclic Xeno Nucleic Acid Oligomers

Xeno nucleic acids (XNAs) are analogues of DNA and RNA that have a non-ribose artificial scaffold. XNAs are possible prebiotic genetic carriers as well as alternative genetic systems in artificial life. In addition, XNA oligomers can be used as biological tools. Acyclic XNAs, which do not have cyclic scaffolds, are attractive due to facile their synthesis and remarkably high nuclease resistance. To maximize the performance of XNAs, a negatively charged backbone is preferable to provide sufficient water solubility; however, acyclic XNAs containing polyanionic backbones suffer from high entropy cost upon duplex formation, because of the high flexibility of the acyclic nature. Herein, we review the relationships between the structure and duplex hybridization properties of various acyclic XNA oligomers with polyanion backbones.