Protecting-Group-Free Total Synthesis and Biological Investigation of Cabucine Oxindole A

Owing to their challenging structures and promising biological profiles,spirooxindole alkaloids have long attracted much attention from the synthetic community.Herein,we wish to describe a concise,protecting-group-free total synthesis of cabucine oxindole A,a putative natural spirooxindole alkaloid and a possible biosynthetic congener of cabucine and palmirine.Key transformations of our approach include a one-step,organocatalytic and enantioselective construction of the spiro[pyrrolidine-3,3'-oxindole]moiety and a Korte rearrangement to furnish the final dihydropyran motif.Biological investigation of 1 and its synthetic intermediates revealed lactone 2 as a mild MOLT-4 and MCF7 cell line inhibitor.

Development of a highly-specific ^(18)F-labeled irreversible positron emission tomography tracer for monoacylglycerol lipase mapping

As a serine hydrolase,monoacylglycerol lipase(MAGL) is principally responsible for the metabolism of 2-arachidonoylglycerol(2-AG) in the central nervous system(CNS),leading to the formation of arachidonic acid(AA).Dysfunction of MAGL has been associated with multiple CNS disorders and symptoms,including neuroinflammation,cognitive impairment,epileptogenesis,nociception and neurodegenerative diseases.Inhibition of MAGL provides a promising therapeutic direction for the treatment of these conditions,and a MAGL positron emission tomography(PET) probe would greatly facilitate preclinical and clinical development of MAGL inhibitors.Herein,we design and synthesize a small library of fluoropyridyl-containing MAGL inhibitor candidates.Pharmacological evaluation of these candidates by activity-based protein profiling identified 14 as a lead compound,which was then radiolabeled with fluorine-18 via a facile SNAr reaction to form 2-[^(18)F]fluoropyridine scaffold.Good blood-brain barrier permeability and high in vivo specific binding was demonstrated for radioligand [^(18)F]14(also named as [^(18)F]MAGL-1902).This work may serve as a roadmap for clinical translation and further design of potent 18F-labeled MAGL PET tracers.

[^(18)F]MAGL-4-11 positron emission tomography molecular imaging of monoacylglycerol lipase changes in preclinical liver fibrosis models

Monoacylglycerol lipase(MAGL) is a pivotal enzyme in the endocannabinoid system, which metabolizes 2-arachidonoylglycerol(2-AG) into the proinflammatory eicosanoid precursor arachidonic acid(AA). MAGL and other endogenous cannabinoid(EC) degrading enzymes are involved in the fibrogenic signaling pathways that induce hepatic stellate cell(HSC) activation and ECM accumulation during chronic liver disease. Our group recently developed an;F-labeled MAGL inhibitor([18F]MAGL-4-11)for PET imaging and demonstrated highly specific binding in vitro and in vivo. In this study, we determined [18F]MAGL-4-11 PET enabled imaging MAGL levels in the bile duct ligation(BDL) and carbon tetrachloride(CCl_(4)) models of liver cirrhosis;we also assessed the hepatic gene expression of the enzymes involved with EC system including MAGL, NAPE-PLD, FAAH and DAGL that as a function of disease severity in these models;[18F]MAGL-4-11 autoradiography was performed to assess tracer binding in frozen liver sections both in animal and human. [18F]MAGL-4-11 demonstrated reduced PET signals in early stages of fibrosis and further significantly decreased with disease progression compared with control mice. We confirmed MAGL and FAAH expression decreases with fibrosisseverity, while its levels in normal liver tissue are high;in contrast, the EC synthetic enzymes NAPE-PLD and DAGL are enhanced in these different fibrosis models. In vitro autoradiography further supported that[18F]MAGL-4-11 bound specifically to MAGL in both animal and human fibrotic liver tissues. Our PET ligand [18F]MAGL-4-11 shows excellent sensitivity and specificity for MAGL visualization in vivo and accurately reflects the histological stages of liver fibrosis in preclinical models and human liver tissues.