RESUMEN

The peptide recifin A is the inaugural member of the structurally intriguing new fold referred to as a tyrosine-lock. Its central four stranded ß-sheet is stabilized by a unique arrangement in which three disulfide bonds and their interconnecting backbone form a ring that wraps around one of the strands, resulting in a Tyr side chain being buried in the molecular core. Here we aimed to establish a synthetic route to this complex class of natural products. Full length recifin A was successfully generated through native chemical ligation chemistry joining two 21 amino acid residue fragments. Surprisingly, reduced linear recifin A readily adopts the correct, topologically-complex fold via random oxidation of the cysteines, suggesting it is highly energetically favored. Utilizing our synthetic strategy, we generated five recifin A analogues to investigate the structural role of the central Tyr residue and provide the first insights into the structure activity relationship of recifin A towards its cancer target tyrosyl-DNA phosphodiesterase I.

RESUMEN

Criteria for predicting the druglike properties of "beyond Rule of 5" Proteolysis Targeting Chimeras (PROTAC) degraders are underdeveloped. PROTAC components are often combined via amide couplings due to their reliability. Amides, however, can give rise to poor absorption, distribution, metabolism, and excretion (ADME) properties. We hypothesized that a bioisosteric amide-to-ester substitution could lead to improvements in both physicochemical properties and bioactivity. Using model compounds, bearing either amides or esters, we identify parameters for optimal lipophilicity and permeability. We applied these learnings to design a set of novel amide-to-ester-substituted, VHL-based BET degraders with the goal to increase permeability. Our ester PROTACs retained intracellular stability, were overall more potent degraders than their amide counterparts, and showed an earlier onset of the hook effect. These enhancements were driven by greater cell permeability rather than improvements in ternary complex formation. This largely unexplored amide-to-ester substitution provides a simple strategy to enhance PROTAC permeability and bioactivity and may prove beneficial to other beyond Ro5 molecules.

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RESUMEN

Cordyheptapeptide A is a lipophilic cyclic peptide from the prized Cordyceps fungal genus that shows potent cytotoxicity in multiple cancer cell lines. To better understand the bioactivity and physicochemical properties of cordyheptapeptide A with the ultimate goal of identifying its cellular target, we developed a solid-phase synthesis of this multiply N-methylated cyclic heptapeptide which enabled rapid access to both side chain- and backbone-modified derivatives. Removal of one of the backbone amide N-methyl (N-Me) groups maintained bioactivity, while membrane permeability was also preserved due to the formation of a new intramolecular hydrogen bond in a low dielectric solvent. Based on its cytotoxicity profile in the NCI-60 cell line panel, as well as its phenotype in a microscopy-based cytological assay, we hypothesized that cordyheptapeptide was acting on cells as a protein synthesis inhibitor. Further studies revealed the molecular target of cordyheptapeptide A to be the eukaryotic translation elongation factor 1A (eEF1A), a target shared by other lipophilic cyclic peptide natural products. This work offers a strategy to study and improve cyclic peptide natural products while highlighting the ability of these lipophilic compounds to effectively inhibit intracellular disease targets.

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Proteolysis targeting chimeras (PROTACs) are catalytic heterobifunctional molecules that can selectively degrade a protein of interest by recruiting a ubiquitin E3 ligase to the target, leading to its ubiquitylation and degradation by the proteasome. Most degraders lie outside the chemical space associated with most membrane-permeable drugs. Although many PROTACs have been described with potent activity in cells, our understanding of the relationship between structure and permeability in these compounds remains limited. Here, we describe a label-free method for assessing the permeability of several VH032-based PROTACs and their components by combining a parallel artificial membrane permeability assay (PAMPA) and a lipophilic permeability efficiency (LPE) metric. Our results show that the combination of these two cell-free membrane permeability assays provides new insight into PROTAC structure-permeability relationships and offers a conceptual framework for predicting the physicochemical properties of PROTACs in order to better inform the design of more permeable and more effective degraders.

RESUMEN

Large macrocyclic peptides can achieve surprisingly high membrane permeability, although the properties that govern permeability in this chemical space are only beginning to come into focus. We generated two libraries of cyclic decapeptides with stable cross-ß conformations, and found that peptoid substitutions within the ß-turns of the macrocycle preserved the rigidity of the parent scaffold, whereas peptoid substitutions in the opposing ß-strands led to "chameleonic" species that were rigid in nonpolar media but highly flexible in water. Both rigid and chameleonic compounds showed high permeability over a wide lipophilicity range, with peak permeabilities differing significantly depending on scaffold rigidity. Our findings indicate that modulating lipophilicity can be used to engineer favorable ADME properties into both rigid and flexible macrocyclic peptides, and that scaffold rigidity can be used to tune optimal lipophilicity.

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As drug discovery moves increasingly toward previously "undruggable" targets such as protein-protein interactions, lead compounds are becoming larger and more lipophilic. Although increasing lipophilicity can improve membrane permeability, it can also incur serious liabilities, including poor water solubility, increased toxicity, and faster metabolic clearance. Here we introduce a new efficiency metric, especially relevant to "beyond rule of 5" molecules, that captures, in a simple, unitless value, these opposing effects of lipophilicity on molecular properties. Lipophilic permeability efficiency (LPE) is defined as log D7.4dec/w - mlipocLogP + bscaffold, where log D7.4dec/w is the experimental decadiene-water distribution coefficient (pH 7.4), cLogP is the calculated octanol-water partition coefficient, and mlipo and bscaffold are scaling factors to standardize LPE values across different cLogP metrics and scaffolds. Using a variety of peptidic and nonpeptidic macrocycle drugs, we show that LPE provides a functional assessment of the efficiency with which a compound achieves passive membrane permeability at a given lipophilicity.

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