Over the past 30 years, enantioselective catalysis has become one of the most important frontiers in exploratory organic synthetic research. During this time, remarkable advances have been made in the development of organometallic asymmetric catalysts that in turn have provided a wealth of enantioselective oxidation, reduction, π-bond activation, and Lewis acid-catalyzed processes. 1 Surprisingly, however, relatively few asymmetric transformations have been reported which employ organic molecules as reaction catalysts, 2 despite the widespread availability of organic chemicals in enantiopure form and the accordant potential for academic, industrial, and economic benefit. Herein, we introduce a new strategy for organocatalysis that we expect will be amenable to a range of asymmetric transformations. In this context, we document the first highly enantioselective organocatalytic Diels-Alder reaction. 3 We recently embarked upon the development of a general strategy for organocatalytic reactions based upon design features derived from the arena of Lewis acid catalysis. Specifically, we reasoned that (i) LUMO-lowering activation and (ii) the kinetic lability toward ligand substitution that enables Lewis acid-catalyst turnover (eq 1) might also be available with a carbogenic system that exists as a rapid equilibrium between an electron-deficient and a relatively electron-rich state. With this in mind, we hypothesized that the reversible formation of iminium ions from R,β-unsaturated aldehydes and amines (eq 2) might emulate the equilibrium dynamics and π-orbital electronics that are inherent to Lewis acid catalysis, thereby providing a new platform for the design of organocatalytic processes. Significantly, this analysis reveals the attractive prospect that chiral amines might function as enantioselective catalysts for a range of transformations that traditionally utilize metal salts.

Heteroarenes are important structural moieties in many chemical industry fields. A highly efficient Pd/Cu-catalyzed C-H arylation method for a range of heterocycles has been discovered. It was found that the key to the success of this transformation is a combination of a palladium catalyst and a well-defined copper cocatalyst. The efficiency and low loadings of catalyst (0.25 mol %) and cocatalyst (1 mol %) together with the mild reaction conditions demonstrate this method to be practically useful and mechanistically interesting.

Structural characterization was performed on an antibody-drug conjugate (ADC), composed of an IgG1 monoclonal antibody (mAb), mertansine drug (DM1), and a noncleavable linker. The DM1 molecules were conjugated through nonspecific modification of the mAb at solvent-exposed lysine residues. Due to the nature of the lysine conjugation process, the ADC molecules are heterogeneous, containing a range of species that differ with respect to the number of DM1 per antibody molecule. The DM1 distribution profile of the ADC was characterized by electrospray ionization mass spectrometry (ESI-MS) and capillary isoelectric focusing (cIEF), which showed that 0-8 DM1s were conjugated to an antibody molecule. By taking advantage of the high-quality MS/MS spectra and the accurate mass detection of diagnostic DM1 fragment ions generated from the higher-energy collisional dissociation (HCD) approach, we were able to identify 76 conjugation sites in the ADC, which covered approximately 83% of all the putative conjugation sites. The diagnostic DM1 fragment ions discovered in this study can be readily used for the characterization of other ADCs with maytansinoid derivatives as payload. Differential scanning calorimetric (DSC) analysis of the ADC indicated that the conjugation of DM1 destabilized the C(H)2 domain of the molecule, which is likely due to conjugation of DM1 on lysine residues in the C(H)2 domain. As a result, methionine at position 258 of the heavy chain, which is located in the C(H)2 domain of the antibody, is more susceptible to oxidation in thermally stressed ADC samples when compared to that of the naked antibody.

Antibody-drug conjugates (ADC) target cytotoxic drugs to antigen-positive cells for treating cancer. After internalization, ADCs with noncleavable linkers are catabolized to amino acidlinker-warheads within the lysosome, which then enter the cytoplasm by an unknown mechanism. We hypothesized that a lysosomal transporter was responsible for delivering noncleavable ADC catabolites into the cytoplasm. To identify candidate transporters, we performed a phenotypic shRNA screen with an anti-CD70 maytansine-based ADC. This screen revealed the lysosomal membrane protein SLC46A3, the genetic attenuation of which inhibited the potency of multiple noncleavable antibodymaytansine ADCs, including ado-trastuzumab emtansine. In contrast, the potencies of noncleavable ADCs carrying the structurally distinct monomethyl auristatin F were unaffected by SLC46A3 attenuation. Structure-activity experiments suggested that maytansine is a substrate for SLC46A3. Notably, SLC46A3 silencing led to relative increases in catabolite concentrations in the lysosome. Taken together, our results establish SLC46A3 as a direct transporter of maytansine-based catabolites from the lysosome to the cytoplasm, prompting further investigation of SLC46A3 as a predictive response marker in breast cancer specimens. Cancer Res; 75(24); 5329-40. Ó2015 AACR.

Early process development and salt selection for AMG 837, a novel GPR40 receptor agonist, is described. The synthetic route to AMG 837 involved the convergent synthesis and coupling of two key fragments, (S)-3-(4-hydroxyphenyl)hex-4-ynoic acid (1) and 3-(bromomethyl)-4 0 -(trifluoromethyl)biphenyl (2). The chiral β-alkynyl acid 1 was prepared in 35% overall yield via classical resolution of the corresponding racemic acid (()-1. An efficient and scalable synthesis of (()-1 was achieved via a telescoped sequence of reactions including the conjugate alkynylation of an in situ protected Meldrum's acid derived acceptor prepared from 3. The biaryl bromide 2 was prepared in 86% yield via a 2-step SuzukiÀMiyaura couplingÀbromination sequence. Chemoselective phenol alkylation mediated by tetrabutylphosphonium hydroxide allowed direct coupling of 1 and 2 to afford AMG 837. Due to the poor physiochemical stability of the free acid form of the drug substance, a sodium salt form was selected for early development, and a more stable, crystalline hemicalcium salt dihydrate form was subsequently developed. Overall, the original 12-step synthesis of AMG 837 was replaced by a robust 9-step route affording the target in 25% yield.