Mycobacterium tuberculosis (Mtb) is the deadliest bacterial pathogen in the world. An estimated one-third of humans harbor Mtb in a dormant state. These asymptomatic, latent infections impede tuberculosis eradication due to the long-term potential for reactivation. Dormant Mtb has reduced enzymatic activity, but hydrolases that remain active facilitate pathogen survival. We targeted Mtb esterases, a diverse set of enzymes in the serine hydrolase family, and studied their activities using both activity-based probes (ABPs) and fluorogenic esterase substrates. These small-molecule probes revealed functional esterases in active, dormant, and reactivating cultures. Using ABPs, we identified five esterases that remained active in dormant Mtb, including LipM (Rv2284), LipN (Rv2970c), CaeA (Rv2224c), Rv0183, and Rv1683. Three of these, CaeA, Rv0183, and Rv1683, were catalytically active in all three culture conditions. Fluorogenic probes additionally revealed LipH (Rv1399c), Culp1 (Rv1984c), and Rv3036c esterase activity in dormant and active cultures. Esterases with persistent activity are potential diagnostic biomarkers or therapeutic targets for Mtb-infected individuals with latent or active tuberculosis.
α-Quaternary ketones are accessed through novel enantioselective alkylations of allyl and propargyl electrophiles by unstabilized prochiral enolate nucleophiles in the presence of palladium complexes with various phosphinooxazoline (PHOX) ligands. Excellent yields and high enantiomeric excesses are obtained from three classes of enolate precursors: enol carbonates, enol silanes, and racemic β-ketoesters. Each of these substrate classes functions with nearly identical efficiency in terms of yield and enantioselectivity. Catalyst discovery and development, the optimization of reaction conditions, the exploration of reaction scope, and applications in target-directed synthesis are reported. Experimental observations suggest that these alkylation reactions occur through an unusual inner-sphere mechanism involving binding of the prochiral enolate nucleophile directly to the palladium center.
Enzyme-activated, fluorogenic probes are powerful tools for studying bacterial pathogens, including Mycobacterium tuberculosis (Mtb). In prior work, we reported two 7-hydroxy-9H-(1,3-dichloro-9,9-dimethylacridin-2-one) (DDAO)-derived acetoxymethyl ether probes for esterase and lipase detection. Here, we report four-carbon (C4) and eight-carbon (C8) acyloxymethyl ether derivatives, which are longer-chain fluorogenic substrates. These new probes demonstrate greater stability and lipase reactivity than the two-carbon (C2) acetoxymethyl ether-masked substrates. We used these new C4 and C8 probes to profile esterases and lipases from Mtb. The C8-masked probes revealed a new esterase band in gel-resolved Mtb lysates that was not present in lysates from nonpathogenic M. bovis (bacillus Calmette-Guérin), a close genetic relative. We identified this Mtb-specific enzyme as the secreted esterase Culp1 (Rv1984c). Our C4- and C8-masked probes also produced distinct Mtb banding patterns in lysates from Mtb-infected macrophages, demonstrating the potential of these probes for detecting Mtb esterases that are active during infections.
A catalytic enantioselective approach to the eudesmane sesquiterpenoids is reported. The strategic use of a palladium-catalyzed enantioselective alkylation of vinylogous ester substrates forged the C (10) all-carbon quaternary center. This key transformation enabled a diastereoselective olefin hydrogenation to create the syn stereochemistry at C(7). The devised synthetic strategy allowed for the preparation of the antibacterial agent (+)-carissone and a formal synthesis of the P/Q-type calcium channel blocker (-)-α-eudesmol.The flowering plants of the family Asteraceae (Compositae) have many historical uses, including rubber, medicines, edible oils, vegetables, and pesticides. 1 Among these flora are a large number of species that are abundant in structurally diverse sesquiterpenoids, particularly ones that contain the eudesmane skeleton (Figure 1). Over 1000 eudesmanes have been identified from these sources, with their structures diverging based on oxygenation and oxidation patterns within the carbon framework.This ever-growing 2 class of important secondary metabolites possesses a wide range of biological properties, including plant growth inhibition, insect antifeedant, antibacterial, antifungal, and antitumor activities. Representative eudesmanes include antibacterial agents (+)-carissone (1) 3 and (+)-3-oxocostusic acid (2), 4 as well as P/Q-type calcium channel blocker (−)-α-eudesmol (3) 5 (Figure 1). These examples typify common structural motifs within this class of sesquiterpenoids, including the C(10) all-carbon quaternary stereocenter and stoltz@caltech.edu. In devising a strategy for the total synthesis of the eudesmanes, we simplified our target to enone 5, which has been utilized in the preparation of structures such as 4, 6d and itself embodies many features present in various family members (cf. 5 and 1, 2) ( Figure 2). We envisioned that the stereochemistry of the C(7) substituent could arise by means of the diastereoselective hydrogenation of a substituted cyclohexene (i.e., 6), the stereochemical outcome of which would be controlled by the C(10) quaternary stereocenter. This cyclohexene could be obtainable from a ring-closing methathesis of triolefin 7, which would be derived from an appropriately substituted α-quaternary ketone (i.e., 8). Thus, the key control element in the design of this synthetic strategy is the C(10) quaternary stereocenter, 10 and we therefore sought to develop an efficient and selective means for the preparation of this moiety. NIH Public AccessThe enantioselective alkylation of ketone enolates is an area of intense investigation in our laboratory. 11 This method has resulted in the preparation of wide range of carbonyl compounds with adjacent quaternary stereocenters with high levels of selectivity and excellent yields, some of which have proved valuable in synthetic endeavors. 12 The application of α-quaternary ketones such as 8 for the devised strategy would require a carbonyl transposition (i.e., 8 → 7), and we therefore chose to exploit the unique propert...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.