Discovery of a Potent Adenine–Benzyltriazolo–Pleuromutilin Conjugate with Pronounced Antibacterial Activity against MRSA

Abstract

Conjugation of pleuromutilin is an attractive strategy for development of novel antibiotics and the fight against multi-resistant bacteria as the class is associated with low rates of resistance and cross-resistance development. Herein, the preparation of 35 novel (+)-pleuromutilin conjugates is reported. Their design was based on a synthetically more efficient benzyl-adaption of a potent lead, but still relied on the Cu(I)-catalysed alkyne-azide [3+2] cycloaddition for conjugation onto pleuromutilin. Their antibacterial activity was evaluated against the multi-resistant Staphylococcus 2 aureus strain USA300 for which they displayed moderate to excellent activity. Compound 35, bearing a para-benzyladenine substituent proved particularly potent against USA300 as well as additional strains of MRSA and displayed as importantly no cytotoxicity in four mammalian cell lines. Structure-activity relationship analysis revealed that the purine 6-amino is essential for high potency, likely due to strong hydrogen bonding with the RNA backbone of C2469 as suggested by a molecular model based on the MM-GBSA approach. 9 Alkylation of the nucleobases (thymine, adenine, 6-chloropurine and 2-amino-chloropurine) was achieved in the presence of an inorganic base (K2CO3 or NaH) in DMF. The yields for 68-78 were mainly deteriorated by lack of regioselectivity, i.e. formation of the N3 isomer (thymines) or N7 isomer (purines), which in turn also complicated their subsequent separation during Flash Chromatography. The strategy was overall still more efficient and straightforward than our previous approach.The chloropurins 74-78 were converted via nucleophilic aromatic substitution with various amines in anhydrous EtOH to grant 79-86, generally in excellent yields. Compound 87 was prepared via guanidination in accordance with a procedure optimized by Česnek and coworkers. 35 The primary benzylamines 89 and 96-97 were synthesized via two strategies (Scheme 3); the para analogue 89 via standard Gabriel synthesis, which proved highly efficient, simultaneously also granting the phthalimide 88. The second strategy involved reduction of ethynylbenzonitriles with LiAlH4, 36 which also proved efficient, granting the nitriles 94 and 95 as well. Scheme 3.Reagents and conditions: (a) K-phthalimide, DMF, rt.; (b) H2N-NH2  H2O 50-60% w/w, EtOH, 78 o C; (a) Trimethylsilylacetylene, Pd(PPh3)4, CuI, Anh. Piperidine 80 o C; (d) K2CO3, MeOH, rt.; (e) i) 1 M LiAlH4 in THF, THF, -10 o C → rt. ii) H2O, NaOH (sat.).

Discovery of Novel Pleuromutilin Derivatives as Potent Antibacterial Agents for the Treatment of MRSA Infection

“…Tiamulin was used as the positive control in this experiment. The minimum inhibitory concentration (MIC) values of the pleuromutilin derivatives 8-30 and tiamulin were determined using the broth dilution methods according to the Clinical and Laboratory Standards Institute (CLSI) [20]. The results of these studies are summarized in 0.03/0.12 0.12/0.25 0.12/0.5 0.25/0.5 9 0.06/0.25 0.25/0.5 0.12/0.5 0.5/1 10 0.12/0.12 0.12/0.25 0.125/0.5 0.25/0.5…”

“…The minimal inhibitory concentration (MIC) of the target pleuromutilin derivatives against methicillin-resistant S. aureus (ATCC 43300), S. aureus (ATCC 29213), S. aureus (AD3) and S. aureus (144) were determined by using tiamulin as the positive control. MIC values were tested following our previous work [20]. The derivatives were dissolved in an aqueous solution of 2.5% tween-80 and 2.5% DMSO to make a solution with a concentration of 1000 µg/mL.…”

“…The MBC of these pleuromutilin derivatives were tested according to a previously reference [20]. After recording the MIC value, the 96-well plate was placed for 22-26 h at 37 • C. Then, the values of MBC were determined by laying 100 µL aliquots from the wells onto the MH agar plates without visible growth.…”

Identification of novel nematode succinate dehydrogenase inhibitors: Virtual screening based on ligand‐pocket interactions

“…The pharmacophore-based design has become a major component of the pesticide discovery process. The pharmacophore model studying ligand-pocket interactions embraces not only the necessary chemical features but also essential features targeting a certain protein (Heidtmann et al, 2020). Because of the excellent activity against nematodes, fluopyram was used for pharmacophore modeling studies.…”

On drug discovery against infectious diseases and academic medicinal chemistry contributions

“…Indeed, this compound was first prepared at Nabriva in 2006 [141,142], and was approved for human use in 2019 [143,144]. The still ongoing story [145] of pleuromutilins illustrates again how long a successful discovery process can take. Concerning one last class of large spectrum antibiotics, there are noteworthy reports which describe the extensive rescaffolding efforts aiming at the discovery of original fluoroquinolone-like antibiotics [146][147][148].…”