To better understand the Structure-activity relationship, SALI was used in the chosen cluster and 4 activity cliffs were detected (Fig. 2). Cliff C1 suggests that the phenyl group must be in a specific configuration to be more active (3, pIC50 = 5.7). Such configuration is also important for the methyl substituent (7, pIC50 = 6.6). Methyl substituted esters (9, pIC50 = 6.6) and amides (10, pIC50 = 5.0) are more potent when compared carboxyl (8, pIC50 = 4.2) or N,N-dimethyl groups (11, pIC50 = 4.0). The pointed out that ester analogues are readily converted to its less potent derivative carboxylic acid [15], so primary amides are preferable due to the higher stability.
Molecular dynamics and docking simulations were used to estimate how α-phenylglycinamides inhibitors may bind to hTRMP8. We found two uncertain binding poses for ligand (2) used as template. One of the binding poses (Pose 2, Fig. 3) according to the interaction energy with the binding pocket possibly is more favorable when compared to (Pose 1, Fig. 3). A net 28.3 kJ mol− 1 (~ 6.8 kcal mol− 1) is gained upon simultaneous cation-π interaction between ARG832 and ligand (2) aromatic moieties. Furthermore, the primary amine can make two hydrogen bond interaction with ASN732 and ASP772. Pose 1 hydrogen bond interaction are prone to occur with TYR995 and ASP793. Less effective aromatic interaction can be formed with TYR736 (Pose 1) and with PHE1003 (Pose 2).
Once the reasonable binding mode was estimated, all molecules were aligned according to compound (2). 3D and 2D descriptors, once filtered, were concatenated in order to build models with S-MLR with high leave-one-out cross-validation correlation coefficient (Q2LOO > 0.5) [30]. The prediction power was tested against an external data set (Q2EXT, n = 14) to attest its usefulness as hTRMP8 pIC50 activity predictor. The best showed Q2LOO = 0.86 and Q2EXT = 0.75 (Fig. 4).
On Fig. 4 3D descriptors LJ1 demonstrated that the presence of a methyl group in the region is better than the absence of groups. An example of this is the better performance of the (1) molecule in this descriptor. Another information acquired is that the presence of an ethyl group provides worse performance than the absence of groups. This factor shows that small-volume groups are best in this region. The next descriptor, HF1, indicates that the presence of indane brings better activity than benzene alone. This can be observed by the better activity in the region of the (2) molecule when compared to (1). The addition of this group generates a repositioning of the ring that favors its activity, indicating the already expected hydrophobicity of the region. HF2 correlates to the presence of an ester group as observed in the (9), giving the same information as in the cliff C3.
The 2D descriptors part of the model are also list in Fig. 4. The GATS4s is a local spatial correlation index in a molecule whose resulting high values are related to the presence of electronegative atoms. It is also related to the probability of intermolecular interaction in the form of hydrogen bonds. When its value is > 1, electronegative atoms are distributed throughout the molecule and there is no local correlation[34]. The AATSC3s and ATSC8i are weighted average centered Broto-Moreau Autocorrelation, and VR1_Dzv (Randic-like eigenvector-based index) are harder to interpret [35]. The other descriptors such as nsssCH refers to the number of -CH moieties present in each molecule, related possibly to the same interpretation as in HF1.
About 61 (supporting information) new prototypes were designed. All planned compounds were design as readily accessible Uri reaction reactants [16]. Among them, 5 obtained more expressive values (pIC50 > 7.0) (Table 1). Regarding the pharmacokinetic evaluations, all prototypes have the characteristic of high gastrointestinal absorption and two are estimated to have high blood-brain barrier permeation.