Synthesis and Evaluation of Marine Natural Product-Inspired Meroterpenoids with Selective Activity toward Dormant Mycobacterium tuberculosis

Abstract

Tuberculosis is a disease caused primarily by the organism Mycobacterium tuberculosis ( Mtb ), which claims about 1.5 million lives every year. A challenge that impedes the elimination of this pathogen is the ability of Mtb to remain dormant after primary infection, thus creating a reservoir for the disease in the population that reactivates under more ideal conditions. A better understanding of the physiology of dormant Mtb and therapeutics able to kill these phenotypically tolerant bacilli will be critical for completely eradicating Mtb . Our groups are focusing on characterizing the activity of derivatives of the marine natural product (+)-puupehenone ( 1 ). Recently, the Rohde group reported that puupehedione ( 2 ) and 15-α-methoxypuupehenol ( 3 ) exhibit enhanced activity in an in vitro multi-stress dormancy model of Mtb. To optimize the antimycobacterial activity of these terpenoids, novel 15-α-methoxy- and 15-α-acetoxy-puupehenol esters were prepared from (+)-puupehenone ( 1 ) accessed through a (+)-sclareolide-derived β-hydroxyl aldehyde. For added diversity, various congeners related to ( 1 ) were also prepared from a common borono-sclareolide donor, which resulted in the synthesis of epi -puupehenol and the natural products (+)-chromazonarol and (+)-yahazunol. In total, we generated a library of 24 compounds, of which 14 were found to be active against Mtb , and the most active compounds retained the enhanced activity against dormant Mtb seen in the parent compound. Several of the 15-α-methoxy- and 15-α-acetoxy-puupehenol esters possessed potent activity against actively dividing and dormant Mtb . Intriguingly, the closely related triisobutyl derivative 16 showed similar activity to 1 in actively dividing Mtb but lost about 178-fold activity against dormant Mtb . However, the monopivaloyl compound 13 showed a modest 3- to 4-fold loss in activity in both actively dividing and dormant Mtb relative to the activity of 1 revealing the importance of the free OH at C19 supporting the potential role of quinone methide formation as critical for activity in dormant Mtb . Elucidating important structure–activity relationships and the mechanism of action of this natural product-inspired chemical series may yield insights into vulnerable drug targets in dormant bacilli and new therapeutics to more effectively target dormant Mtb .

Evaluation of Derivatives of (+)-Puupehenone against Clostridioides difficile and Other Gram-Positive Bacteria

“…We previously synthesized a library of 20 compounds to be screened for activity against several Gram-positive and Gram-negative bacteria. 35 The structures of these compounds are shown in Figure 1 . Several of these compounds had promising activity against C. difficile and other Gram-positive bacteria, as seen in Table 1 .…”

“…We previously synthesized a library of 20 compounds to be screened for activity against several Gram-positive and Gram-negative bacteria . The structures of these compounds are shown in Figure .…”

“…34 Based on that report, we created a chemical library of (+)-puupehenone derivatives with the intent of finding a more potent compound that could serve as a foundation for further investigation and structure–activity relationship studies. 35 We then challenged C. difficile and other bacterial species with this library to evaluate their effects on organisms implicated in HAIs. Additionally, knowing that fidaxomicin inhibits C. difficile toxin production, 36 we wanted to investigate if these compounds could modulate the expression of these toxins in a similar fashion.…”

“…difficile . Based on that report, we created a chemical library of (+)-puupehenone derivatives with the intent of finding a more potent compound that could serve as a foundation for further investigation and structure–activity relationship studies . We then challenged C.…”

Proton Motive Force-Disrupting Antimycobacterial Guanylurea Polymer

“…An Mtb CDC1551 derived strain 29 and Mab strains (rough and smooth morphotype) 30,31 containing the autoluminescent reporter plasmid pMV306hsp +LuxG13 (a gift from Brian Robertson and Siouxsie Wiles−Addgene plasmid #26161; http://n2t.net/addgene:26161; RRID:Addg-ene_26161) were used in this study as previously described. 28 Mtblux was cultured in Middlebrook 7H9 supplemented with 0.05% Tween 80 and 10% oleic acid/albumin/dextrose/catalase (OADC) and incubated stationary at 37 °C and 5% CO 2 . Kanamycin (103 μM, KAN) was added to maintain the reporter plasmid.…”