Urotensin II((4-11)) Azasulfuryl Peptides: Synthesis and Biological Activity.

Cyclic azasulfuryl (As) peptide analogs of the urotensin II (UII, 1, H-Glu-Thr-Pro-Asp-c[Cys-Phe-Trp-Lys-Tyr-Cys]-Val-OH) fragment 4-11 were synthesized to explore the influences of backbone structure on biological activity. N-Aminosulfamides were inserted as surrogates of the Trp(7) and Lys(8) residues in the biologically relevant Trp-Lys-Tyr triad. A combination of solution- and solid-phase methods were used to prepare novel UII((4-11)) analogs 6-11 by routes featuring alkylation of azasulfuryl-glycine tripeptide precursors to install various side chains. The pharmacological profiles of derivatives 6-11 were tested in vitro using a competitive binding assay and ex vivo using a rat aortic ring bioassay. Although the analogs exhibited weak affinity for the urotensin II receptor (UT) without agonistic activity, azasulfuryl-UII((4-11)) derivatives 7-9 reduced up to 50% of the effects of UII and urotensin II-related peptide (URP) without affecting their potency.

De Novo Conception of Small Molecule Modulators Based on Endogenous Peptide Ligands: Pyrrolodiazepin-2-one γ-Turn Mimics That Differentially Modulate Urotensin II Receptor-Mediated Vasoconstriction ex Vivo.

A proof-of-concept library of pyrrolodiazepinone small molecules was designed based on the Bip-Lys-Tyr motif found in a recently described modulator of the urotensinergic system. Solid-phase synthesis provided 13 analogues, which were tested for their ability to modulate selectively and differentially the potency (EC50) and efficacy (E(max)) of hUII and URP ex vivo in a rat aortic ring bioassay. Notably, at 14 µM, pyrrolodiazepinone R-4a inhibited completely hUII-induced contractions and increased URP-associated vasoconstriction. Pyrrolodiazepinone R-4a represents, to the best of our knowledge, a first-in-class small molecule that exerts a probe-dependent effect on hUII and URP biological activities and proves that UT modulators of the urotensin II receptor (UT) can be rationally designed. The importance of the UT system in the pathogenesis and progression of cardiovascular diseases highlights the utility of pyrrolodiazepinones such as R-4a, which exhibit promising potential as tools for differentiating the respective roles, signaling pathways, and phenotypic outcomes of UII and URP in the UT system.

Pyrrolo[3,2-e][1,4]diazepin-2-one synthesis: a head-to-head comparison of soluble versus insoluble supports.

Aryldiazepin-2-ones are known as "privileged structures", because they bind to multiple receptor types with high affinity. Toward the development of a novel class of aryldiazepin-2-one scaffolds, the synthesis of pyrrolo[3,2-e][1,4]diazepin-2-ones on a support was explored starting from N-(PhF)-4-hydroxyproline and featuring an acid-catalyzed Pictet-Spengler reaction to form the diazepine ring. Three supports [Wang resin, tetraarylphosphonium (TAP) soluble support, and Merrifield resin] were examined in the synthesis of the heterocycle and exhibited different advantages and disadvantages. Wang resin proved effective for exploratory optimization of the synthesis by identification of intermediates after resin cleavage under mild conditions; however, the acidic conditions of the Pictet-Spengler reaction caused premature loss of resin-bound material. Direct monitoring of reactions by TLC, RP-HPLC-MS, and in certain cases NMR spectroscopy was possible with the TAP support, which facilitated purification of intermediates by precipitation; however, incomplete precipitation of material led to overall yields lower than those from solid-phase approaches on resin. Merrifield resin proved stable to the conditions for the synthesis of the pyrrolo[3,2-e][1,4]diazepin-2-one targets and would be amenable to "split-and-mix" chemistry; however, relatively harsh conditions were necessary for final product cleavage. Perspective for the application of different solid-phase approaches in heterocycle library synthesis was thus obtained by demonstration of the respective utility of the three supports for preparation of pyrrolo[3,2-e][1,4]diazepin-2-one.