Synthesis, Biological Evaluation, and 3D QSAR Study of 2-Methyl-4-oxo-3-oxetanylcarbamic Acid Esters as N-Acylethanolamine Acid Amidase (NAAA) Inhibitors

Abstract

N-(2-Oxo-3-oxetanyl)carbamic acid esters have recently been reported to be noncompetitive inhibitors of the Nacylethanolamine acid amidase (NAAA) potentially useful for the treatment of pain and inflammation. In the present study, we further explored the structure−activity relationships of the carbamic acid ester side chain of 2-methyl-4-oxo-3-oxetanylcarbamic acid ester derivatives. Additional favorable features in the design of potent NAAA inhibitors have been found together with the identification of a single digit nanomolar inhibitor. In addition, we devised a 3D QSAR using the atomic property field method. The model turned out to be able to account for the structural variability and was prospectively validated by designing, synthesizing, and testing novel inhibitors. The fairly good agreement between predictions and experimental potency values points to this 3D QSAR model as the first example of quantitative structure−activity relationships in the field of NAAA inhibitors.

Potent α-amino-β-lactam carbamic acid ester as NAAA inhibitors. Synthesis and structure–activity relationship (SAR) studies

“…A limited exploration of this structural feature was carried out by decreasing (3f) or increasing (3g) the linear chain of carbamate 3b by a methylene unit. Unexpectedly, both compounds turned out to be slightly more potent (3f: IC 50 ¼ 0.044 mM; 3g: IC 50 ¼ 0.049 mM, Table 3) than 3b, differently to what we observed in the b-lactone carbamate series [37,38].…”

“…While the increase in potency observed with compound 3c is in accordance with the SAR observed in a-amino-b-lactone carbamate derivatives, where long alkyl chains are preferred over short ones [38], the detrimental effect of a 5-phenylpentyl or a p-biphenylmethyl group differentiates the SAR of b-lactam carbamate derivatives from that of the corresponding b-lactone series. We then explored the replacement of the long unsubstituted alkyl chain with a short, u-cycloalkyl-substituted chain, a moiety that led to potent NAAA inhibitors in the a-amino-b-lactone series [37,38]. The introduction of a 4-cyclohexylbutyl group yielded compound 3b, which allowed recovering double-digit nanomolar potency, while reducing the length of the alkyl chain.…”

“…On the basis of the results of the SAR studies on the b-lactone carbamate [37,38] and b-lactam amide [42] classes, we learned that NAAA inhibition could be affected by varying the length of the aliphatic side chain. A limited exploration of this structural feature was carried out by decreasing (3f) or increasing (3g) the linear chain of carbamate 3b by a methylene unit.…”

“…Most of the used alcohols were commercially available (11bef,l,n,p,r,y,z,ab,ac,ae,aj) or prepared by reduction of the corresponding commercially available precursors (11g,s,v,w,aa,ad,af,ak,al, see Supporting Information). The remaining alcohols were either obtained following previously reported protocols (11i [53], j [54], t [55], u [56], ah [37], see Supporting Information) or synthesized as described in Schemes 5 and 6 (11h,k,m,o,q,x,ag,ai,am).…”

Molecular mechanism of activation of the immunoregulatory amidase NAAA

“…Although NAAA was discovered (35), cloned (39), and purified (15) almost 20 years ago, questions regarding its mechanism of action remain unanswered due to a lack of structural information. Homology models have been built (27,43) and employed for inhibitor development (20,44,45). Such models are, however, of little heuristic value because they rely on a bacterial homolog sharing only 13% sequence identity with NAAA.…”