Expanding Reactivity in DNA-Encoded Library Synthesis via Reversible Binding of DNA to an Inert Quaternary Ammonium Support

Abstract

DNA Encoded Libraries have proven immensely powerful tools for lead identification. The ability to screen billions of compounds at once has spurred increasing interest in DEL development and utilization. Although DEL provides access to libraries of unprecedented size and diversity, the idiosyncratic and hydrophilic nature of the DNA tag severely limits the scope of applicable chemistries. It is known that biomacromolecules can be reversibly, noncovalently adsorbed and eluted from solid supports, and this phenomenon has been utilized to perform synthetic modification of biomolecules in a strategy we have described as reversible adsorption to solid support (RASS). Herein, we present the adaptation of RASS for a DEL setting, which allows reactions to be performed in organic solvents at near anhydrous conditions opening previously inaccessible chemical reactivities to DEL. The RASS approach enabled the rapid development of C(sp²)-C(sp³) decarboxylative cross-couplings with broad substrate scope, an electrochemical amination (the first electrochemical synthetic transformation performed in a DEL context), and improved reductive amination conditions. The utility of these reactions was demonstrated through a DEL-rehearsal in which all newly developed chemistries were orchestrated to afford a compound rich in diverse skeletal linkages. We believe that RASS will offer expedient access to new DEL reactivities, expanded chemical space, and ultimately more drug-like libraries.

Figure 1.

DEL Synthesis via RASS. (A) Aqueous vs RASS reactions for DEL. (B) Resins selection considerations. (C) Basic DEL RASS workflow. DNA binding and elution of DNA by HPLC

Figure 2.

On-DNA Decarboxylative sp²-sp³ Cross-Coupling. (A) Reaction Scheme. (B) Optimization Table; ^a Reactions include small molecule reactions under DEL conditions and on-DNA DEL reactions (C) Scope Table; ^a Protocol A (18 hr), ^b Protocol B (2 × 3 hr), ^c Isolated RAE, ^d 1:1 desired rroduct:reduced product.

Figure 3.

On-DNA Electrochemical Amination. (A) Reaction Scheme. (B) Optimization Table (C) Scope Table, ^a Conditions from Entry 6, ^b Conditions from Entry 6 + DBU (100 mM).

Figure 4.

On-DNA Reductive Amination. (A) Reaction Scheme. (B) Optimization Table, ^a Reactions conducted by Pfizer and results communicated through personal communications (C) Scope Table, ^a On Resin, ^b Aqueous Reaction.

Figure 5.

DEL—Rehearsal, Graphical Workflow Representation and Synthesis of 90.

Figure 6.

Structural Insights. Confocal Microscopy Image of Resin with (A) Double Stranded DNA (B) Single Stranded DNA Adsorbed and Stained with SYBR Green. (C) Quantification of Resin Fluorescence.