Synthesis of the sponge-derived plakortone series of bioactive compounds.

The Caribbean sponges of the genus Plakortis, P. halichondrioides, and P. simplex have provided a series of biologically active furanolactones-the plakortones A-D (1-4) from the former sponge and B-F (2-6) from the latter. The defining motif of the plakortones is a sterically congested 2,6-dioxabicyclo[3.3.0]octan-3-one moiety, the emblematic furanolactone core. This core is efficiently accessed by a palladium(II) mediated hydroxycyclization-carbonylation-lactonization cascade with an appropriate ene-1,3-diol. Total syntheses of plakortones C (3) and F (6) are now described which settle constitutional and stereochemical features in this group of secondary metabolites. Acquisition of plakortone D (4), the most effective activator of SR-Ca(2+)-pumping ATPase, utilized stereodefined lactone cores that resulted from asymmetric dihydroxylation of protected homoallylic alcohol 29. A derived lactone aldehyde was then coupled with an independently generated, sulfone-activated side chain unit, 57. The 11,12-E-double bond, carried through the sequence as a protected, stereodefined diol, was released therefrom by stereospecific syn-elimination via an orthoester derivative. In this way, plakortone D (4) was demonstrated to possess the (3S,4S,6S,10R,11E) configuration. Racemic plakortone E (5) was also acquired by using the Pd(II) induced sequence, but in this case, the required, complete acyclic system 52 was assembled first. Plakortone C (3) resulted from a sequence commencing with (R)-(+)-3-hydroxy-2-methylpropionate, with a derived iodide 76 alkylating the enolate of the butyramide 77 generated from (1S,2S)-(+)-pseudoephedrine. The liberated primary alcohol 79 was converted by standard procedures to key enediol 89 which, with the Pd(II) protocol, afforded the major separable plakortones 90 and 91, with the former being identical with natural plakortone C (3). Very mild hydrogenation of 90 afforded a saturated plakortone, identical with natural plakortone F (6), thus establishing its structure and absolute stereochemistry. Available information on the stereoselective routes to plakortones E (5) and B (2) are also outlined, so that the constitution and absolute stereochemistry of plakortones B-F are now established.

Spiroacetal biosynthesis in insects from Diptera to Hymenoptera: the Giant Ichneumon wasp Megarhyssa nortoni nortoni Cresson.

The volatile components of the mandibular gland secretion generated by the Giant Ichneumon parasitoid wasp Megarhyssa nortoni nortoni Cresson are mainly spiroacetals and methyl ketones, and all have an odd number of carbon atoms. A biosynthetic scheme rationalizing the formation of these diverse components is presented. This scheme is based on the results of incorporation studies using (2)H-labeled precursors and [(18)O]dioxygen. The key steps are postulated to be decarboxylation of beta-ketoacid equivalents, beta-oxidation (chain shortening), and monooxygenase-mediated hydroxylation leading to a putative ketodiol that cyclizes to spiroacetals. The generality of the role of monooxygenases in spiroacetal formation in insects is considered, and overall, a cohesive, internally consistent theory of spiroacetal generation by insects is presented, against which future hypotheses will have to be compared.

Creation of a Novel Class of Potent and Selective MutT Homologue 1 (MTH1) Inhibitors Using Fragment-Based Screening and Structure-Based Drug Design.

Recent literature has both suggested and questioned MTH1 as a novel cancer target. BAY-707 was just published as a target validation small molecule probe for assessing the effects of pharmacological inhibition of MTH1 on tumor cell survival, both in vitro and in vivo. (1) In this report, we describe the medicinal chemistry program creating BAY-707, where fragment-based methods were used to develop a series of highly potent and selective MTH1 inhibitors. Using structure-based drug design and rational medicinal chemistry approaches, the potency was increased over 10,000 times from the fragment starting point while maintaining high ligand efficiency and drug-like properties.

Novel Class of Potent and Cellularly Active Inhibitors Devalidates MTH1 as Broad-Spectrum Cancer Target.

MTH1 is a hydrolase responsible for sanitization of oxidized purine nucleoside triphosphates to prevent their incorporation into replicating DNA. Early tool compounds published in the literature inhibited the enzymatic activity of MTH1 and subsequently induced cancer cell death; however recent studies have questioned the reported link between these two events. Therefore, it is important to validate MTH1 as a cancer dependency with high quality chemical probes. Here, we present BAY-707, a substrate-competitive, highly potent and selective inhibitor of MTH1, chemically distinct compared to those previously published. Despite superior cellular target engagement and pharmacokinetic properties, inhibition of MTH1 with BAY-707 resulted in a clear lack of in vitro or in vivo anticancer efficacy either in mono- or in combination therapies. Therefore, we conclude that MTH1 is dispensable for cancer cell survival.

Creation of Novel Cores for ß-Secretase (BACE-1) Inhibitors: A Multiparameter Lead Generation Strategy.

In order to find optimal core structures as starting points for lead optimization, a multiparameter lead generation workflow was designed with the goal of finding BACE-1 inhibitors as a treatment for Alzheimer's disease. De novo design of core fragments was connected with three predictive in silico models addressing target affinity, permeability, and hERG activity, in order to guide synthesis. Taking advantage of an additive SAR, the prioritized cores were decorated with a few, well-characterized substituents from known BACE-1 inhibitors in order to allow for core-to-core comparisons. Prediction methods and analyses of how physicochemical properties of the core structures correlate to in vitro data are described. The syntheses and in vitro data of the test compounds are reported in a separate paper by Ginman et al. [J. Med. Chem. 2013, 56, 4181-4205]. The affinity predictions are described in detail by Roos et al. [J. Chem. Inf. 2014, DOI: 10.1021/ci400374z].

Core refinement toward permeable ß-secretase (BACE-1) inhibitors with low hERG activity.

By use of iterative design aided by predictive models for target affinity, brain permeability, and hERG activity, novel and diverse compounds based on cyclic amidine and guanidine cores were synthesized with the goal of finding BACE-1 inhibitors as a treatment for Alzheimer's disease. Since synthesis feasibility had low priority in the design of the cores, an extensive synthesis effort was needed to make the relevant compounds. Syntheses of these compounds are reported, together with physicochemical properties and structure-activity relationships based on in vitro data. Four crystal structures of diverse amidines binding in the active site are deposited and discussed. Inhibitors of BACE-1 with 3 µM to 32 nM potencies in cells are shown, together with data on in vivo brain exposure levels for four compounds. The results presented show the importance of the core structure for the profile of the final compounds.

New aminoimidazoles as ß-secretase (BACE-1) inhibitors showing amyloid-ß (Aß) lowering in brain.

Amino-2H-imidazoles are described as a new class of BACE-1 inhibitors for the treatment of Alzheimer's disease. Synthetic methods, crystal structures, and structure-activity relationships for target activity, permeability, and hERG activity are reported and discussed. Compound (S)-1m was one of the most promising compounds in this report, with high potency in the cellular assay and a good overall profile. When guinea pigs were treated with compound (S)-1m, a concentration and time dependent decrease in Aß40 and Aß42 levels in plasma, brain, and CSF was observed. The maximum reduction of brain Aß was 40-50%, 1.5 h after oral dosing (100 µmol/kg). The results presented highlight the potential of this new class of BACE-1 inhibitors with good target potency and with low effect on hERG, in combination with a fair CNS exposure in vivo.