An experimental approach is described for late-stage lead diversification of frontrunner drug candidates using nanomole-scale amounts of lead compounds for structure−activity relationship development. The process utilizes C−H bond activation methods to explore chemical space by transforming candidates into newly functionalized leads. A key to success is the utilization of microcryoprobe nuclear magnetic resonance (NMR) spectroscopy, which permits the use of low amounts of lead compounds (1−5 μmol). The approach delivers multiple analogues from a single lead at nanomole-scale amounts as DMSO-d 6 stock solutions with a known structure and concentration for in vitro pharmacology and absorption, distribution, metabolism, and excretion testing. To demonstrate the feasibility of this approach, we have used the antihistamine agent loratadine (1). Twenty-six analogues of loratadine were isolated and fully characterized by NMR. Informative SAR analogues were identified, which display potent affinity for the human histamine H 1 receptor and improved metabolic stability.

The trioxacarcins are polyoxygenated, structurally complex natural products that potently inhibit the growth of cultured human cancer cells. Here we describe syntheses of trioxacarcin A, DC-45-A1, and structural analogs by latestage, stereoselective glycosylation reactions of fully functionalized, differentially protected aglycon substrates. Key issues addressed in this work include the identification of an appropriate means to activate and protect each of the two 2-deoxysugar components, trioxacarcinose A and trioxacarcinose B, as well as a viable sequencing of the glycosidic couplings. The convergent, component-based sequence we present allows for rapid construction of structurally diverse, synthetic analogs that would be inaccessible by any other means, in amounts required to support biological evaluation. Analogs arising from modification of four of five modular components are assembled in 11 steps or fewer. The majority of these are found to be active in antiproliferative assays using cultured human cancer cells.The trioxacarcins are bacterial metabolites of remarkable structural complexity that broadly inhibit the growth of cultured bacterial and eukaryotic cells. [1][2][3][4][5] A number of unusual chemical features characterize the family, including a rigid, highly oxygenated polycyclic skeleton with a fused spiro epoxide function, as many as five ketal or hemiketal groups (three of them within a span of four contiguous carbon atoms) and one or more unusual glycosidic residues, eponymously identified as "trioxacarcinoses". The most potent family member yet identified, trioxacarcin A (Figure 1), displays subnanomolar IC 70 values in a number of different human cancer cell lines. Its extraordinary antiproliferative effects are believed to derive from the fact that trioxacarcin A efficiently and irreversibly alkylates G residues of duplex DNA, forming a covalent bond between the exocyclic carbon atom of the spiro epoxide function and N7 of the G residue that is alkylated. Both the DNA lesion and the product of depurination that is formed from it upon heating, a 1:1 adduct of guanine and Users may view, print, copy, download and text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use: http://www.nature.com/authors/editorial_policies/license.html#termsCorrespondence and requests for materials should be addressed to A.G.M. * myers@chemistry.harvard.edu Reprints and permission information is available online at http://npg.nature.com/reprintsandpermissions/. Additional information:The authors declare no competing financial interests.Supplementary information and chemical compound information accompany this paper at www.nature.com/naturechemistry. HHS Public Access Author ManuscriptAuthor Manuscript Author ManuscriptAuthor Manuscript trioxacarcin A ("gutingimycin"), 6 have been crystallographically characterized in seminal work from researchers at the University of Göttingen. 7Although so far as we are aware trioxacarcins have...

Two routes to the 2,6-dideoxysugar methyl trioxacarcinoside A are described. Each was enabled by an apparent α-chelation-controlled addition of an allylmetal reagent to a ketone substrate containing a free α-hydroxyl group and a β-hydroxyl substituent, either free or protected as the corresponding di-tert-butylmethyl silyl ether. Both routes provide practical access to gram-quantities of trioxacarcinose A in a form suitable for glycosidic coupling reactions.

For all the promise of and need for clinical drug-induced liver injury (DILI) risk screening systems, demonstrating the predictive value of these systems versus readily available physicochemical properties and inherent dosing information has not been thoroughly evaluated. Therefore, we utilized a systematic approach to evaluate the predictive value of in vitro safety assays including Bile Salt Export Pump (BSEP) transporter inhibition and cytotoxicity in HepG2 and transformed human liver epithelial (THLE) along with physicochemical properties. We also evaluated the predictive value of in vitro ADME assays including hepatic partition coefficient (Kp) and its unbound counterpart since they provide insight on hepatic accumulation potential. The datasets comprised of 569 marketed drugs with FDA DILIrank annotation (Most vs Less/None), dose and physicochemical information, 384 drugs with Kp and plasma protein binding data, and 279 drugs with safety assay data. For each dataset and combination of input parameters, we developed random forest machine learning models and measured model performance using the receiver operator characteristic area-under-the-curve (ROC AUC). The median ROC AUC across the various data and parameters sets ranged from 0.67 to 0.77 with little evidence of additive predictivity when including safety or ADME assay data. Subsequent machine learning models consistently demonstrated daily dose, fraction sp3 or ionization, and cLogP/D inputs produced the best, simplest model for predicting clinical DILI risk with an ROC AUC of 0.75. This systematic framework should be used for future assay predictive value assessments and highlights the need for continued improvements to clinical DILI risk annotation.

An efficient 4-step synthetic route to the useful chiral building block (2R,3S)-dihydroxybutyric acid acetonide of >95% ee is detailed. The sequence is readily scaled, requires no chromatography, and allows for efficient recycling of p-phenylbenzyl alcohol, an expedient for enantio- and diastereoenrichment by recrystallization.