Stereochemical Structure Activity Relationship Studies (S-SAR) of Tetrahydrolipstatin

Synthetic Efforts and Ultimate Limitation to an Asymmetric Achmatowicz Approach Toward EBC-23

An effort toward the total synthesis of the polyketide natural product EBC-23 is reported. The asymmetric approach is convergent and uses a late-stage Claisen-like enolate/acid chloride coupling to establish a key 1,3-diketone intermediate. The 1,3-diketone target is an oxidized form of the hydrated natural product, which fails to spiroketalize. The convergent asymmetric synthesis uses an asymmetric Noyori transfer hydrogenation of a β-furyl ketoester to enantioselectively form a chiral furyl alcohol. An Achmatowicz/Jones/Luche three-step reaction sequence was used to stereoselectively convert the furyl alcohol into the 5-hydroxy-pyran-2-one. The absolute stereochemistry of the 1,3-polyol fragment was established by a Leighton allylation. A subsequent Grubbs cross-metathesis, and Evans acetalation were used to install the 1,3-syn-diol stereochemistry.

Total Synthesis of Tetrahydrolipstatin, Its Derivatives, and Evaluation of Their Ability to Potentiate Multiple Antibiotic Classes against Mycobacterium Species

Tetrahydrolipstatin (THL, 1a) has been shown to inhibit both mammalian and bacterial α/β hydrolases. In the case of bacterial systems, THL is a known inhibitor of several Mycobacterium tuberculosis hydrolases involved in mycomembrane biosynthesis. Herein we report a highly efficient eight-step asymmetric synthesis of THL using a route that allows modification of the THL α-chain substituent to afford compounds 1a through 1e. The key transformation in the synthesis was use of a (TPP)CrCl/Co2(CO)8-catalyzed regioselective and stereospecific carbonylation on an advanced epoxide intermediate to yield a trans-β-lactone. These compounds are modest inhibitors of Ag85A and Ag85C, two α/β hydrolases of M. tuberculosis involved in the biosynthesis of the mycomembrane. Among these compounds, 10d showed the highest inhibitory effect on Ag85A (34 ± 22 μM) and Ag85C (66 ± 8 μM), and its X-ray structure was solved in complex with Ag85C to 2.5 Å resolution. In contrast, compound 1e exhibited the best-in-class MICs of 50 μM (25 μg/mL) and 16 μM (8.4 μg/mL) against M. smegmatis and M. tuberculosis H37Ra, respectively, using a microtiter assay plate. Combination of 1e with 13 well-established antibiotics synergistically enhanced the potency of few of these antibiotics in M. smegmatis and M. tuberculosis H37Ra. Compound 1e applied at concentrations 4-fold lower than its MIC enhanced the MIC of the synergistic antibiotic by 2-256-fold. In addition to observing synergy with first-line drugs, rifamycin and isoniazid, the MIC of vancomycin against M. tuberculosis H37Ra was 65 μg/mL; however, the MIC was lowered to 0.25 μg/mL in the presence of 2.1 μg/mL 1e demonstrating the potential of targeting mycobacterial hydrolases involved in mycomembrane and peptidoglycan biosynthesis.

Pancreatic triglyceride lipase mediates lipotoxic systemic inflammation

Visceral adipose tissue plays a critical role in numerous diseases. Although imaging studies often show adipose involvement in abdominal diseases, their outcomes may vary from being a mild self-limited illness to one with systemic inflammation and organ failure. We therefore compared the pattern of visceral adipose injury during acute pancreatitis and acute diverticulitis to determine its role in organ failure. Acute pancreatitis-associated adipose tissue had ongoing lipolysis in the absence of adipocyte triglyceride lipase (ATGL). Pancreatic lipase injected into mouse visceral adipose tissue hydrolyzed adipose triglyceride and generated excess nonesterified fatty acids (NEFAs), which caused organ failure in the absence of acute pancreatitis. Pancreatic triglyceride lipase (PNLIP) increased in adipose tissue during pancreatitis and entered adipocytes by multiple mechanisms, hydrolyzing adipose triglyceride and generating excess NEFAs. During pancreatitis, obese PNLIP-knockout mice, unlike obese adipocyte-specific ATGL knockouts, had lower visceral adipose tissue lipolysis, milder inflammation, less severe organ failure, and improved survival. PNLIP-knockout mice, unlike ATGL knockouts, were protected from adipocyte-induced pancreatic acinar injury without affecting NEFA signaling or acute pancreatitis induction. Therefore, during pancreatitis, unlike diverticulitis, PNLIP leaking into visceral adipose tissue can cause excessive visceral adipose tissue lipolysis independently of adipocyte-autonomous ATGL, and thereby worsen organ failure.

Total and Formal Syntheses of Fostriecin

Two formal syntheses and one total synthesis of fostriecin (1) have been achieved, as well as, the synthesis of its related congener dihydro-dephospho-fostriecin. All the routes use the Sharpless dihydroxylation to set the absolute stereochemistry at C-8/9 positions and a Leighton allylation to set the C-5 position of the natural product. In the formal syntheses a Noyori transfer hydrogenation of an ynone was used to set the C-11 position while the total synthesis employed a combination of asymmetric dihydroxylation and Pd-π-allyl reduction to set the C-11 position. Finally in the total synthesis, a trans-hydroboration of the C-12/13 alkyne was used in combination with a Suzuki cross coupling to establish the Z,Z,E-triene of fostriecin (1).

Synthesis and direct comparison of the anticancer activities of phomopsolides D and E and two 7-oxa-/7-aza-analogues

The synthesis of two stable phomopsolide natural products (D and E) and two analogues is presented. The cytotoxicities of these four compounds are surveyed and compared across a panel of NCI-cancer cell lines. This analysis found moderate cytotoxicities (2-50 μM) for the majority of the cell lines with phomopsolide D being more active than phomopsolide E and the 7-oxa analogue being commensurately more active than the 7-aza analogue.

Stereodivergent Synthesis of Chiral Paraconic Acids via Dynamic Kinetic Resolution of 3-Acylsuccinimides

A direct N-heterocyclic carbene (NHC) catalysis of maleimides with alkyl aldehydes is established for the synthesis of 3-acylsuccinimides. The first dynamic kinetic resolution of 3-acylsuccinimides is accomplished through asymmetric transfer hydrogenation. These two catalytic methodologies are utilized for the synthesis of each enantiomer of trans-paraconic acids in three steps and cis-paraconic acids in four steps with good yields and high stereoselectivities. This stereodivergent synthetic methodology is applied for the synthesis of seven bioactive paraconic acid natural products.

Discovery of arginine-containing tripeptides as a new class of pancreatic lipase inhibitors

Aim: The inhibition of pancreatic lipase (PL) represents one of the most promising strategies in the search for novel antiobesity drugs. We propose here a pioneering course by exploring tripeptide scaffolds in the way to selective PL inhibitors. Methodology/Results: The peptide series exhibited good PL inhibitory properties in vitro, with all the strongest inhibitors sharing a central arginine, shown in silico to be relevant for the active site-directed activity. The compounds were found devoid of inhibitory properties on acetylcholinesterase. Conclusion: Present results disclosed that basic tripeptides are able to interact efficiently with the PL-binding pocket, where they adopt a binding pose suitable for functional-to-inhibition interactions with key amino acids. Main inhibitor MALA4 may be selected as lead for further optimization.

1,10-Secoguaianolides from Artemisia austro-yunnanensis and Their Anti-Inflammatory Effects

Seven 1,10-secoguaianolides 1⁻7, including a new one (compound 1), were isolated from Artemisia austro-yunnanensis and identified by HRESIMS and other spectroscopic methods. Their anti-inflammatory effects were evaluated by the model of LPS-induced RAW264.7 cells in vitro. Bioassay results showed that six of them (1⁻4, 6 and 7), with the exception of 5, produce some cytotoxicity on RAW264.7 cells at its high dosage, can significantly decrease the release of NO, TNF-α, IL-1β, IL-6 and PGE2 in a dose dependent manner, and down-regulate the expression of proteins iNOS and COX-2. The mechanism study indicated they regulated the NF-κB dependent transcriptional activity through decreasing the phosphorylation of NF-κB. Further, the relationship between their structures and cytokines to anti-inflammatory were studied by PCA and discussed.

Characterization of Tetrahydrolipstatin and Stereoderivatives on the Inhibition of Essential Mycobacterium tuberculosis Lipid Esterases

Tetrahydrolipstatin (THL) is a covalent inhibitor of many serine esterases. In mycobacteria, THL has been found to covalently react with 261 lipid esterases upon treatment of Mycobacterium bovis cell lysate. However, the covalent adduct is considered unstable in some cases because of the hydrolysis of the enzyme-linked THL adduct resulting in catalytic turnover. In this study, a library of THL stereoderivatives was tested against three essential Mycobacterium tuberculosis lipid esterases of interest for drug development to assess how the stereochemistry of THL affects respective enzyme inhibition and allows for cross enzyme inhibition. The mycolyltransferase Antigen 85C (Ag85C) was found to be stereospecific with regard to THL; covalent inhibition occurs within minutes and was previously shown to be irreversible. Conversely, the Rv3802 phospholipase A/thioesterase was more accepting of a variety of THL configurations and uses these compounds as alternative substrates. The reaction of the THL stereoderivatives with the thioesterase domain of polyketide synthase 13 (Pks13-TE) also leads to hydrolytic turnover and is nonstereospecific but occurs on a slower, multihour time scale. Our findings suggest the stereochemistry of the β-lactone ring of THL is important for cross enzyme reactivity, while the two stereocenters of the peptidyl arm can affect enzyme specificity and the catalytic hydrolysis of the β-lactone ring. The observed kinetic data for all three target enzymes are supported by recently published X-ray crystal structures of Ag85C, Rv3802, and Pks13-TE. Insights from this study provide a molecular basis for the kinetic modulation of three essential M. tuberculosis lipid esterases by THL and can be applied to increase potency and enzyme residence times and enhance the specificity of the THL scaffold.