Fully automated fast-flow synthesis of antisense phosphorodiamidate morpholino oligomers.

Rapid development of antisense therapies can enable on-demand responses to new viral pathogens and make personalized medicine for genetic diseases practical. Antisense phosphorodiamidate morpholino oligomers (PMOs) are promising candidates to fill such a role, but their challenging synthesis limits their widespread application. To rapidly prototype potential PMO drug candidates, we report a fully automated flow-based oligonucleotide synthesizer. Our optimized synthesis platform reduces coupling times by up to 22-fold compared to previously reported methods. We demonstrate the power of our automated technology with the synthesis of milligram quantities of three candidate therapeutic PMO sequences for an unserved class of Duchenne muscular dystrophy (DMD). To further test our platform, we synthesize a PMO that targets the genomic mRNA of SARS-CoV-2 and demonstrate its antiviral effects. This platform could find broad application not only in designing new SARS-CoV-2 and DMD antisense therapeutics, but also for rapid development of PMO candidates to treat new and emerging diseases.

Amide-forming chemical ligation via O-acyl hydroxamic acids.

The facile rearrangement of "S-acyl isopeptides" to native peptide bonds via S,N-acyl shift is central to the success of native chemical ligation, the widely used approach for protein total synthesis. Proximity-driven amide bond formation via acyl transfer reactions in other contexts has proven generally less effective. Here, we show that under neutral aqueous conditions, "O-acyl isopeptides" derived from hydroxy-asparagine [aspartic acid-ß-hydroxamic acid; Asp(ß-HA)] rearrange to form native peptide bonds via an O,N-acyl shift. This process constitutes a rare example of an O,N-acyl shift that proceeds rapidly across a medium-size ring (t1/2 ∼ 15 min), and takes place in water with minimal interference from hydrolysis. In contrast to serine/threonine or tyrosine, which form O-acyl isopeptides only by the use of highly activated acyl donors and appropriate protecting groups in organic solvent, Asp(ß-HA) is sufficiently reactive to form O-acyl isopeptides by treatment with an unprotected peptide-αthioester, at low mM concentration, in water. These findings were applied to an acyl transfer-based chemical ligation strategy, in which an unprotected N-terminal Asp(ß-HA)-peptide and peptide-αthioester react under aqueous conditions to give a ligation product ultimately linked by a native peptide bond.

Rational Design of Selective and Bioactive Inhibitors of the Mycobacterium tuberculosis Proteasome.

The 20S core particle of the proteasome in Mycobacterium tuberculosis (Mtb) is a promising, yet unconventional, drug target. This multimeric peptidase is not essential, yet degrades proteins that have become damaged and toxic via reactions with nitric oxide (and/or the associated reactive nitrogen intermediates) produced during the host immune response. Proteasome inhibitors could render Mtb susceptible to the immune system, but they would only be therapeutically viable if they do not inhibit the essential 20S counterpart in humans. Selective inhibitors of the Mtb 20S were designed and synthesized on the bases of both its unique substrate preferences and the structures of substrate-mimicking covalent inhibitors of eukaryotic proteasomes called syringolins. Unlike the parent syringolins, the designed analogues weakly inhibit the human 20S (Hs 20S) proteasome and preferentially inhibit Mtb 20S over the human counterpart by as much as 74-fold. Moreover, they can penetrate the mycobacterial cell envelope and render Mtb susceptible to nitric oxide-mediated stress. Importantly, they do not inhibit the growth of human cell lines in vitro and thus may be starting points for tuberculosis drug development.

Macrocyclization of Unprotected Peptide Isocyanates.

A chemistry for the facile two-component macrocyclization of unprotected peptide isocyanates is described. Starting from peptides containing two glutamic acid γ-hydrazide residues, isocyanates can be readily accessed and cyclized with hydrazides of dicarboxylic acids. The choice of a nucleophilic linker allows for the facile modulation of biochemical properties of a macrocyclic peptide. Four cyclic NYAD-1 analogues were synthesized using the described method and displayed a range of biological activities.

Systematic Investigation of EDC/sNHS-Mediated Bioconjugation Reactions for Carboxylated Peptide Substrates.

1-Ethyl-3-(3-(dimethylamino)propyl)carbodiimide (EDC) bioconjugations have been utilized in preparing variants for medical research. While there have been advances in optimizing the reaction for aqueous applications, there has been limited focus toward identifying conditions and side reactions that interfere with product formation. We present a systematic investigation of EDC/N-hydroxysulfosuccinimide (sNHS)-mediated bioconjugations on carboxylated peptides and small proteins. We identified yet-to-be-reported side products arising from both the reagents and substrates. Model peptides used in this study illustrate particular substrates are more susceptible to side reactions than others. From our studies, we found that bioconjugations are more efficient with high concentrations of amine nucleophile but not sNHS. Performing bioconjugations on a model affibody protein show that the trends established with model peptides hold for more complex systems.

Substrate-guided optimization of the syringolins yields potent proteasome inhibitors with activity against leukemia cell lines.

Natural products that inhibit the proteasome have been fruitful starting points for the development of drug candidates. Those of the syringolin family have been underexploited in this context. Using the published model for substrate mimicry by the syringolins and knowledge about the substrate preferences of the proteolytic subunits of the human proteasome, we have designed, synthesized, and evaluated syringolin analogs. As some of our analogs inhibit the activity of the proteasome with second-order rate constants 5-fold greater than that of the methyl ester of syringolin B, we conclude that the substrate mimicry model for the syringolins is valid. The improvements in in vitro potency and the activities of particular analogs against leukemia cell lines are strong bases for further development of the syringolins as anti-cancer drugs.

Efficient and regiospecific syntheses of peptides with piperazic and dehydropiperazic acids via a multicomponent reaction.

Peptides containing N2-acyl piperazic or 1,6-dehydropiperazic acids can be formed efficiently via a novel multicomponent reaction of 1,4,5,6-tetrahydropyridazines, isocyanides, and carboxylic acids. Remarkably, the reaction's induced intramolecularity can enable the regiospecific formation of products with N2-acyl piperazic acid, which counters the intrinsic and troublesome propensity for piperazic acids to react at N1 in acylations. The utility of the methodology is demonstrated in the synthesis of the bicyclic core of the interleukin-1ß converting enzyme inhibitor, Pralnacasan.

Use of a multicomponent reaction for chemoselective derivatization of multiple classes of metabolites.

We demonstrate that the Ugi reaction enables chemoselective derivatization of biological amines, carboxylic acids, aldehydes, or ketones with a chromophore under one set of reaction conditions, even in the presence of water. Derivatization of neurotransmitters, hormones, disease biomarkers and other metabolites bodes well for systems biology and diagnostic medicine.