Perspectives on the Designation of Oligonucleotide Starting Materials

The designation of starting materials (SMs) for pharmaceuticals has been a topic of great interest and debate since the first ICH quality guidance was published. The increase in the number and variety of commercialized oligonucleotides (antisense oligonucleotides—ASOs, small interfering RNAs—siRNAs, etc.) in recent years has reignited dialogue on this topic because of the unique complexity of the monomeric nucleotides and other contributory materials used to manufacture oligonucleotides. The SM working group in the European Pharma Oligonucleotide Consortium (EPOC) was formed to help establish simple, risk-based criteria to guide the justification of oligonucleotide SMs. This article provides a description of the common types of SMs, classes of SM impurities, and control strategies that will be helpful to maintain manufacturing consistency.

Absorption, metabolism and excretion of cobimetinib, an oral MEK inhibitor, in rats and dogs

1. The absorption, metabolism and excretion of cobimetinib, an allosteric inhibitor of MEK1/2, was characterized in mass balance studies following single oral administration of radiolabeled (¹⁴C) cobimetinib to Sprague-Dawley rats (30 mg/kg) and Beagle dogs (5 mg/kg). 2. The oral dose of cobimetinib was well absorbed (81% and 71% in rats and dogs, respectively). The maximal plasma concentrations for cobimetinib and total radioactivity were reached at 2-3 h post-dose. Drug-derived radioactivity was fully recovered (∼90% of the administered dose) with the majority eliminated in feces via biliary excretion (78% of the dose for rats and 65% for dogs). The recoveries were nearly complete after the first 48 h following dosing. 3. The metabolic profiles indicated extensive metabolism of cobimetinib prior to its elimination. For rats, the predominant metabolic pathway was hydroxylation at the aromatic core. Lower exposures for cobimetinib and total radioactivity were observed in male rats compared with female rats, which was consistent to in vitro higher clearance of cobimetinib for male rats. For dogs, sequential oxidative reactions occurred at the aliphatic portion of the molecule. Though rat metabolism was well-predicted in vitro with liver microsomes, dog metabolism was not. 4. Rats and dogs were exposed to the two major human circulating Phase II metabolites, which provided relevant metabolite safety assessment. In general, the extensive sequential oxidative metabolism in dogs, and not the aromatic hydroxylation in rats, was more indicative of the metabolism of cobimetinib in humans.

A Robust, Recyclable Resin for Decagram Scale Resolution of (±)-Mefloquine and Other Chiral N-Heterocycles

Decagram quantities of enantiopure (+)-mefloquine have been produced via kinetic resolution of racemic mefloquine using a ROMP-gel supported chiral acyl hydroxamic acid resolving agent. The requisite monomer was prepared in a few synthetic steps without chromatography and polymerization was safely performed on a >30 gram scale under ambient conditions. The reagent was readily regenerated and reused multiple times for the resolution of 150 grams of (±)-mefloquine and other chiral N-heterocylces.

Direct Catalytic Asymmetric Aldol Additions of Methyl Ynones. Spontaneous Reversal in the Sense of Enantioinduction

In this Communication, we report the direct, catalytic, asymmetric aldol addition of methyl ynones using our dinuclear zinc catalyst. A spontaneous reversal in the sense of enantioinduction was observed for these reactions; formation of the (S)-enantiomer is favored in the early stages (69% ee after 5 min), whereas the (R)-enantiomer is isolated as the major product after prolonged reaction times (97% ee after 22 h). It could be shown that this reversal in enantioselectivity is due to formation of a new catalytic species which incorporates the aldol product.

Leucascandrolide A: Synthesis and Related Studies

The total synthesis of the biologically active marine natural product leucascandrolide A is reported. A convergent strategy is employed, allowing for the rapid assembly of the macrolide moiety. Key steps of our approach include the diastereoselective addition of a zinc alkynilide to (R)-isopropylidene glyceraldehyde, the enantioselective copper(I) fluoride catalyzed aldol addition of a TMS-dienolate to crotonaldehyde, and the formation of a 2,6-trans-substituted tetrahydropyran by selenium-mediated intramolecular cyclization. Moreover, dramatic solvent effects observed in the macrolactonization reaction suggest that hydrogen-bonding effects play a critical role. An improved route to a key intermediate of our synthesis is documented.