Structure–activity relationship studies of the aromatic positions in cyclopentapeptide CXCR4 antagonists

Abstract

The cyclopentapeptide CXCR4 antagonist FC131 (cyclo(-Arg 1 -Arg 2 -2-Nal 3 -Gly 4 -D-Tyr 5 -), 2; 2-Nal = 3-(2-naphthyl)alanine) represents an excellent starting point for development of novel drug-like ligands with therapeutic potential in HIV, cancer, stem-cell mobilization, inflammation, and autoimmune diseases. While the structure-activity relationships for Arg 1 , Arg 2 , and Gly 4 are well established, less is 10 understood about the roles of the aromatic residues 2-Nal 3 and D-Tyr 5 . Here we report further structureactivity relationship studies of these two positions, which showed that (i) the distal aromatic ring of the 2-Nal 3 side chain is required in order to maintain high potency, and (ii) replacement of D-Tyr 5 with conformationally constrained analogues results in significantly reduced activity. However, a simplified analogue that contained Gly instead of D-Tyr 5 was only 13-fold less potent than 2, which means that the 15 D-Tyr 5 side chain is dispensable. These findings were rationalized based on molecular docking, and the collective structure-activity data for the cyclopentapeptides suggest that appropriately designed Arg 2 -2-Nal 3 dipeptidomimetics have potential as CXCR4 antagonists.

Design, synthesis, and biological evaluation of scaffold-based tripeptidomimetic antagonists for CXC chemokine receptor 4 (CXCR4)

“…11 However, as the D-Phe 5 analogue was found to be only 2-fold less potent, this H-bond is not essential for antagonistic activity; indeed, the Gly 5 analogue of 1 was found to be only one order of magnitude less potent than 1 in our assay system. 11 Collectively, these observations imply that the remaining L-/D-Arg 1 -Arg 2 -2-Nal 3 tripeptide fragment serves as a recognition motif for peptidic CXCR4 antagonists, which motivates further studies of both flexible and constrained small molecules containing this motif. Through dissection of the cyclopentapeptide structure and a stepwise reintroduction of cyclic constraints, we here report the design, synthesis, and biological evaluation of a novel class of scaffold-based tripeptidomimetic CXCR4 antagonists based on the D-Arg-Arg-2-Nal motif.…”

“…Similarly, we have recently shown that replacement of L-2-Nal in position 3 with aromatic/alicyclic analogs results in significant reduction of the antagonistic potency, 11 and therefore used a 2-naphthyl group with the appropriate spacer length for all compounds. In contrast, position 1 has been shown to be relatively tolerant to structural and 0.023 µM, respectively).…”

“…11 Even if our modeling suggested that D-Tyr 5 of 1 is partly solvent exposed, the phenolic hydroxyl group was found to take part in hydrogen bonding to Glu 32 . 11 However, as the D-Phe 5 analogue was found to be only 2-fold less potent, this H-bond is not essential for antagonistic activity; indeed, the Gly 5 analogue of 1 was found to be only one order of magnitude less potent than 1 in our assay system. 11 Collectively, these observations imply that the remaining L-/D-Arg 1 -Arg 2 -2-Nal 3 tripeptide fragment serves as a recognition motif for peptidic CXCR4 antagonists, which motivates further studies of both flexible and constrained small molecules containing this motif.…”

“…9 The Gly 4 residue in the cyclopentapeptide CXCR4 antagonists ( Figure 1) was originally introduced for synthetic reasons 5 and thus can be considered as a spacer. Through SAR studies, it has become clear that the D-Tyr 5 side chain is not essential for biological activity, 10,11 and we have in a recent molecular docking study found that this may stem from the lack of a defined binding pocket for the D-Tyr 5 side chain. 11 Even if our modeling suggested that D-Tyr 5 of 1 is partly solvent exposed, the phenolic hydroxyl group was found to take part in hydrogen bonding to Glu 32 .…”

“…Through SAR studies, it has become clear that the D-Tyr 5 side chain is not essential for biological activity, 10,11 and we have in a recent molecular docking study found that this may stem from the lack of a defined binding pocket for the D-Tyr 5 side chain. 11 Even if our modeling suggested that D-Tyr 5 of 1 is partly solvent exposed, the phenolic hydroxyl group was found to take part in hydrogen bonding to Glu 32 . 11 However, as the D-Phe 5 analogue was found to be only 2-fold less potent, this H-bond is not essential for antagonistic activity; indeed, the Gly 5 analogue of 1 was found to be only one order of magnitude less potent than 1 in our assay system.…”