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The emergence of new therapeutic modalities requires complementary tools for their efficient syntheses. Availability of methodologies for site-selective modification of biomolecules remains a long-standing challenge, given the inherent complexity and the presence of repeating residues that bear functional groups with similar reactivity profiles. We describe a bioconjugation strategy for modification of native peptides relying on high site selectivity conveyed by enzymes. We engineered penicillin G acylases to distinguish among free amino moieties of insulin (two at amino termini and an internal lysine) and manipulate cleavable phenylacetamide groups in a programmable manner to form protected insulin derivatives. This enables selective and specific chemical ligation to synthesize homogeneous bioconjugates, improving yield and purity compared to the existing methods, and generally opens avenues in the functionalization of native proteins to access biological probes or drugs.

Single-stranded silencing RNAs (ss siRNA), while not as potent as duplex RNAs, have the potential to become a novel platform technology in RNA interference based gene silencing by virtue of their simplicity and plausibly favorable characteristics in pharmacokinetics and biodistribution. Like other therapeutic pharmaceutical agents, ss siRNA can be optimized to achieve higher potency through a structure-activity based approach. Systematic chemical modification at each position of a 21-mer oligonucleotide identified 2',5'-linked 3'-deoxythymidine (3dT) at position 1 and locked nucleic acids (LNAs) at the seed region as key components to afford significant enhancement in knockdown activity both in vitro and in vivo. Further optimization by additional chemical modifications should enable ss siRNA as an alternative gene silencing modality., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The realization of polymer conjugate-based RNA delivery as a clinical modality requires the development and optimization of novel formulations. Although many literature examples of polymer conjugate-based SiRNA delivery systems exist, the protocols described herein represent a robust and facile way of screening any poly(amine)-based polymer system for SiRNA delivery. In this chapter, we describe the synthetic methods used to prepare poly(amide) polymers using a controlled polymerization method, as well as the preparation of the resulting targeted SiRNA polymer conjugates. In addition, detailed methods are provided for the characterization of the biodegradable poly(peptides) as well as the polymer conjugate that ensues.