STRUCTURE-ACTIVITY RELATIONSHIP: STUDY OF LEI-401 AS INHIBITOR OF NAPE-PLD BY PHARMACOPHORE MODEL

N-acyl-phosphatidylethanolamine phospholipase D (NAPE–PLD) is considered to be the principal enzyme that produces N-acylethanolamines (NAEs), a family of signaling lipids. NAEs are involved in numerous physiological processes such as appetite, satiety, pain, inflammation, fertility, stress, and anxiety. Furthermore, aberrant NAE levels are associated with metabolic syndrome and non-alcoholic steatohepatitis (NASH). Several inhibitors for NAPE–PLD have been reported. But most of the inhibitors showed poor to moderate potency for NAPE–PLD in vitro. Recently, Mario van der Stelt et al describe the SAR of NAPE–PLD inhibitors that afforded LEI–401 in vitro. However, no attempt was instigated to produce a consensus pharmacophore model of LEI–401 as inhibitors of NAPE–PLD. Pharmacophore modeling is an efficient and useful approach to identify important patterns in a series of molecules for optimizations. The consensus pharmacophore model revealed the importance of structural features and their correlation with the biological activity.

N-acyl-phosphatidylethanolamine phospholipase D (NAPE-PLD) is considered to be the principal enzyme that produces N-acylethanolamines (NAEs), a family of signaling lipids. NAEs are involved in numerous physiological processes such as appetite, satiety, pain, inflammation, fertility, stress, and anxiety. Furthermore, aberrant NAE levels are associated with metabolic syndrome and non-alcoholic steatohepatitis (NASH). Several inhibitors for NAPE-PLD have been reported. But most of the inhibitors showed poor to moderate potency for NAPE-PLD in vitro. Recently, Mario van der Stelt et al describe the SAR of NAPE-PLD inhibitors that afforded LEI-401 in vitro. However, no attempt was instigated to produce a consensus pharmacophore model of LEI-401 as inhibitors of NAPE-PLD. Pharmacophore modeling is an efficient and useful approach to identify important patterns in a series of molecules for optimizations. The consensus pharmacophore model revealed the importance of structural features and their correlation with the biological activity.

Selection of Dataset
The dataset consists of one hundred and sevenpyrimidine and pyridine scaffold derivatives exhibiting the inhibitor activity (pIC 50 ) in µM range. The pyrimidine and pyridine scaffold derivatives possess good variation in substation pattern like the presence of different heterocyclic, aliphatic and aromatic ringsand change in linkers (Mario van der Stelt, et al, 2021). Therefore, the selected dataset is wide enough to develop a consensus pharmacophore model. Out of these the dataset of most active six compounds has been tabulated in table 1.

Result and Discussion:-
From fig. 1 it is seen that, the consensus pharmacophoric pattern of different inhibitors of NAPE-PLD is highlighted by three contour fields. The yellow colour field represented hydrophobic/lipophilic nature, blue colour field represented negative charge nature and red colour field represented positive charge nature of the compound. The present pharmacophore-oriented analysis unveils that the activity of different inhibitors of NAPE-PLD has good correlation with these three contour fields.
From fig. 1 it is observed that, all compounds show two types of hydrophobic/lipophilic field (yellow colour region), one is due to benzene moiety and second is due to cyclopropane ring. Thus, all compounds have similar activity towards hydrophobic/lipophilic nature. One remarkable observation shown by all compounds isexcept LEI-401, Compound-2,3,4,5 and 6 show two types of negative field (blue colour region),it is due to carbonyl group in amideandoxygen atom of morpholine. LEI-401 shows only one type of negative field and it is due to carbonyl group in amide.It is also noted that, allcompounds show variation in activity of positive field (red colour region).Except LEI-401, Compound-2,3,4,5 and 6 show single type of positive field and it is only due to -NH group. Among these, Compound-2and5 show negligible activity ofpositive fielddue to -NH group in amide moiety attached to pyrimidine ring.On the other hand, in Compound-6 activity of positive fieldis slightlyincreased as compared to Compound-2 and 5, this is because of-NH group in amide moiety attached to s-triazine ring.
Although, remarkable increase in the activity of positive field is observed in Compound-4 compared to Compound-2,5 and 6, as a result of -NH group in amide moiety attached to pyridine ring. The most notable observation regarding structural feature related to Compound-3 and 4 is that, Compound-3 shows positive field over secondary -NH group and not over -NH group in amide moiety even though it is attached to pyridine ring while Compound-4 though it is attached to pyridine ring shows positive field over -NH group in amide moiety and over secondary -NH group.This highlights the importance of attachment of skeleton to heterocyclic ring (Pyridine)andactivity of positive field observed in compound-3 and 4.LEI-401 shows two types of activity positive field as compared to Compound-2,3,4,5 and 6 (show single positive field). These two types of positive field in LEI-401 is due to presence of -OH group and-NH group in amide moiety. Thus, the above discussion reveals that, LEI-401 has two types of positive field and only one type of negative field while Compound-2,3,4,5 and 6 have negligible or single type of positive field and two types of negative field.

Conclusion:-
The present work reveals important pharmacophoric patterns ofLEI-401 derivative as inhibitors of NAPE-PLD. It unveils the importance of attachment of -NH group in amide moiety to pyrimidine, pyridine and s-triazine ring. It also highlights the importance of -OH group, secondary -NH group, carbonyl group in amide, oxygen atom of morpholine, cyclopropane ring and aromatic moiety and their correlation with the biological activity.Hence, such a combination of these moieties must be useful in future optimization. The outcomes of this present work could be advantageous to chemists while developing a new drug design.