Structure–Activity Relationships for the N-Me- Versus N-H-Amide Modification to Macrocyclic ent-Verticilide Antiarrhythmics

Abstract

The synthesis of all N-Me and N-H analogues of ent-verticilide is described, enabling a structure−activity relationship study based on cardiac ryanodine receptor (RyR2) calcium ion channel inhibition. The use of permeabilized cardiomyocytes allowed us to correlate the degree of N-methylation with activity without concern for changes in passive membrane permeability that these modifications can cause. A key hypothesis was that the minimal pharmacophore may be repeated in this cyclic oligomeric octadepsipeptide (a 24-membered macrocycle), opening the possibility that target engagement will not necessarily be lost with a single N-Me → N-H modification. The effect in the corresponding 18-membered ring oligomer (ent-verticilide B1) was also investigated. We report here that a high degree of N-methyl amide content is critical for activity in the ent-verticilide series but not entirely so for the ent-verticilide B1 series.

Backbone-Determined Antiarrhythmic Structure–Activity Relationships for a Mirror Image, Oligomeric Depsipeptide Natural Product

“…Figure summarizes these findings; no inhibition of RyR2 (lack of activity) is reflected as a value of 1 (dotted line). The relative activity of Series 1 compounds was reported previously, finding that introduction of one or more N –H amide(s) to the structure leads to loss of measurable activity . In that study, we noted that the 18-membered oligomer was more forgiving.…”

“…The relative activity of Series 1 compounds was reported previously, finding that introduction of one or more N−H amide(s) to the structure leads to loss of measurable activity. 35 In that study, we noted that the 18-membered oligomer was more forgiving. Returning to the 24-membered ring oligomers studied here, Series 2 showed a significant trend, with introduction of a single N−H amide as a replacement for an ester (2.1) producing an analog with modest potency.…”

RyR2 Binding of an Antiarrhythmic Cyclic Depsipeptide Mapped Using Confocal Fluorescence Lifetime Detection of FRET

“…The synthesis of AF568-labeled ent -verticilide (Figure , analog 3 ) was planned from an alkyne-modified ent -verticilide (Figure , analog 2 ), providing a modest structural change that was not expected to affect activity against RyR2 . Two syntheses of ent -verticilide have been reported by us, ,− but the oligomeric nature of 1 simplifies the didepsipeptide monomer synthesis and assembly.…”

RyR2 Binding of an Antiarrhythmic Cyclic Depsipeptide Mapped Using Confocal Fluorescence Lifetime Detection of FRET

“…2 analog 3) was planned from an alkynemodified ent-verticilide (Fig. 2, analog 2), providing a modest structural change that was not expected to affect activity against RyR2 (22). Two syntheses of ent-verticilide have been reported by us (7,(23)(24)(25)(26) but the oligomeric nature of 1 simplifies the didepsipeptide monomer synthesis and assembly.…”