Small-molecule competitors of protein-protein interactions are urgently needed for functional analysis of large-scale genomics and proteomics data. Particularly abundant, yet so far undruggable, targets include domains specialized in recognizing proline-rich segments, including Src-homology 3 (SH3), WW, GYF, and Drosophila enabled (Ena)/vasodilator-stimulated phosphoprotein (VASP) homology 1 (EVH1) domains. Here, we present a modular strategy to obtain an extendable toolkit of chemical fragments (ProMs) designed to replace pairs of conserved prolines in recognition motifs. As proofof-principle, we developed a small, selective, peptidomimetic inhibitor of Ena/VASP EVH1 domain interactions. Highly invasive MDA MB 231 breast-cancer cells treated with this ligand showed displacement of VASP from focal adhesions, as well as from the front of lamellipodia, and strongly reduced cell invasion. General applicability of our strategy is illustrated by the design of an ErbB4-derived ligand containing two ProM-1 fragments, targeting the yes-associated protein 1 (YAP1)-WW domain with a fivefold higher affinity.Ena | VASP | protein-protein interaction | actin cytoskeleton | cell migration

A simple formamide catalyst facilitates the efficient transformation of alcohols into alkyl chlorides with benzoyl chloride as the sole reagent. These nucleophilic substitutions proceed through iminium-activated alcohols as intermediates. The novel method, which can be even performed under solvent-free conditions, is distinguished by an excellent functional group tolerance, scalability (>100 g) and waste-balance (E-factor down to 2). Chiral substrates are converted with excellent levels of stereochemical inversion (99 %→≥95 % ee). In a practical one-pot procedure, the primary formed chlorides can be further transformed into amines, azides, ethers, sulfides, and nitriles. The value of the method was demonstrated in straightforward syntheses of the drugs rac-Clopidogrel and S-Fendiline.

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A practical and scalable synthesis of a Fmoc-protected tricyclic dipeptide mimetic (6), that is, a 1,4-diaza-tricyclo-[8.3.0(3,7)]-tridec-8-ene derivative resembling a rigidified di-L-proline in a polyproline type II (PPII) helix conformation, was developed. The strategy is based on a Ru-catalyzed ring-closing metathesis of a dipeptide (4) prepared by PyBOP coupling of cis-5-vinylproline tert-butylester (2) and trans-N-Boc-3-vinylproline (rac-3) followed by chromatographic diastereomer separation. Building block 2 was prepared from L-proline in six steps via electrochemical C5-methoxylation, cyanation and conversion of the nitrile into a vinyl substituent. Building block rac-3 was prepared in five steps exploiting a Cu-catalyzed 1,4-addition of vinyl-MgBr to a 2,3-dehydroproline derivative in the key step. In the course of the investigation subtle dependencies of protecting groups on the reactivity of the 2,3- and 2,5-disubstituted pyrrolidine derivatives were observed. The configuration and conformational preference of several intermediates were determined by X-ray crystallography. The developed synthesis allows the preparation of substantial amounts of 6, which will be used in the search for new small molecules for the modulation of protein-protein interactions involving proline-rich motifs (PRDs).

A practical four-step synthesis of 3-alkyl-, vinyl-, and aryl-substituted proline derivatives, which are important building blocks for conformationally restrained peptide analogs, was developed. The method relies on a Cu-catalyzed 1,4-addition of Grignard reagents to N-protected 2,3-dehydroproline esters, efficiently prepared in a new one-pot protocol. The 1,4-addition products are obtained with good trans-selectivity (dr 5:1 to 25:1). A nonracemic sample of N-Cbz-3-vinylproline (74% ee) was obtained using Evans oxazolidinone as a chiral auxiliary.