Receptor- and Ligand-Based Study on Novel 2,2′-Bithienyl Derivatives as Non-Peptidic AANAT Inhibitors

Abstract

Arylalkylamine N-acetyl transferase (serotonin N-acetyl transferase, AANAT) is a critical enzyme in the light-mediated regulation of melatonin production and circadian rythm. With the objective of discovering new chemical entities with inhibitory potencies against AANAT, a medium-throughput screening campaign was performed on a chemolibrary. We found a class of molecules based on a 2,2'-bithienyl scaffold, and compound 1 emerged as a first hit. Herein, we describe our progress from hit discovery and to optimization of this new class of compounds. To complete the study, computational approaches were carried out: a docking study which provided insights into the plausible binding modes of these new AANAT inhibitors and a three-dimensional quantitative structure-activity relationship study that applied comparative molecular field analysis (CoMFA) methodology. Several CoMFA models were developed (variable alignments and options), and the best predictive one yields good statistical results (q(2) = 0.744, r(2) = 0.891, and s = 0.273). The resulting CoMFA contour maps were used to illustrate the pharmacomodulations relevant to the biological activities in this series of analogs and to design new active inhibitors. This novel series of 2,2'-bithienyl derivatives gives new insights into the design of AANAT inhibitors.

How Can Molecular Pharmacology Help Understand the Multiple Actions of Melatonin: 20 Years of Research and Trends

“…It was attempting, at one stage, to try to find specific inhibitors of the enzyme, in order to better understand in in situ situations the roles of melatonin at various locations. Several publications including ours reported those efforts [14][15][16][17][18]. If one particular point should be stressed, it is the elegant ways analogues of an intermediary state of the substrate/co-substrate complex permitted to turn molecules into powerful inhibitors, although overall fragile ones [19], as well as the way that the incorporation of an exotic amino acid in place of a serine permitted to stabilize the enzyme, rendered insensitive to proteolysis [20][21][22].…”

Evaluation of Rhodanine Indolinones as AANAT Inhibitors

“…[29] We found there was no gains in potency upon changing the chain length (30-64 μM for 24-26 vs. 27 μM for 17). However, replacing the 5-carbon chain with both phenyl and cyclohexyl rings (27)(28)(29)(30) resulted in a 1.5-3-fold improvement in potency. It is somewhat surprising that all the ring replacements had comparable potency, even though they are joined to the rest of the molecule in subtly different ways.…”

“…[21] Myricetin was purchased from TCI America. Compound 4 was prepared by a Sonogashira coupling [27] between allylpropiolamide [32] and 5-iodo-2,2'-bithiophene. [33] Compounds of Tables 3 and 4 were synthesized by a Knoevenagel condensation between the appropriate 5-membered heterocycle (prepared according to Table 1 or purchased) and isatin or p-fluorobenzyl isatin 16 (Table 2).…”

“…[22][23] Though we did not select 1 and 3, we did use both as positive controls in zebrafish (ZF) studies (below). Bis-thiophene 4 has a relatively low molecular weight (273 g/mol) and was reported to have good cell potency, [27] but in our hands it did not inhibit AANAT enzyme activity at a concentration up to 40 μM. After considering enzymatic potency and overall properties of these published AANAT inhibitors, we selected modestly potent (IC 50 = 27 μM) but cell active (rat pinealocyte cell assay: IC 50 = 100 μM), [20] rhodanine indolinone 17 for optimization.…”

“…Does compound 17 have in vivo activity as expected for an AANAT inhibitor? Previously published AANAT inhibitors [20][21][25][26][27] that we evaluated in our new enzymatic assay before beginning work on modifying 17. IC 50 values reported for sheep AANAT enzyme, unless indicated otherwise.…”