Iridium Acylnitrenoid-Initiated Biomimetic Cascade Cyclizations: Stereodefined Access to Polycyclic δ-Lactams.

Ring-fused azacyclic compounds are important building units in the synthesis of biorelevant natural products, pharmaceutical agents, and molecular materials. Herein, we present a new approach to these condensed azacycles by a biomimetic cascade cyclization of arylalkenyl dioxazolones. This cascade reaction was found to proceed with excellent stereoselectivity and a high functional group tolerance. The substrate scope of arylalkenyl dioxazolones turned out to be highly flexible and extendable to additional terminating subunits, such as heteroaryl and alkynyl moieties. This biomimetic cyclization was elucidated to be initiated by an intramolecular transfer of the in situ generated electrophilic Ir-acylnitrenoid to the tethered olefinic double bond, leading to a key N-acylaziridine intermediate, which is in turn reacted with pendant (hetero)arenes or alkynes in a highly regio- and stereoselective manner to produce ring-fused azacyclic compounds.

Bioinspired Total Synthesis of Pyritide A2 through Pyridine Ring Synthesis.

Pyritides belong to the ribosomally synthesized and post-translationally modified peptide class of natural products that were recently genome-predicted and are structurally defined by unique pyridine-containing macrocycles. Inspired by their biosynthesis, proceeding through peptide modification and cycloaddition to form the heterocyclic core, we report the chemical synthesis of pyritide A2 involving pyridine ring synthesis from an amino acid precursor through aza-Diels-Alder reaction. This strategy permitted the preparation of the decorated pyridine core with an appended amino acid residue in two steps from a commercially available arginine derivative and secured pyritide A2 in ten steps. Moreover, the synthetic logic enables efficient preparation of different pyridine subunits associated with pyritides, allowing rapid and convergent access to this new class of natural products and analogues thereof.

Tetrahydro-1H,5H-pyrazolo[1,2-a]pyrazole-1-carboxylates as inhibitors of Plasmodium falciparum dihydroorotate dehydrogenase.

The reactions between 5-substituted pyrazolidine-3-ones, aldehydes, and methyl methacrylate provided tetrahydropyrazolo[1,2-a]pyrazole-1-carboxylates as mixtures of syn- and anti-diastereomers. Testing for inhibition of dihydroorotate dehydrogenase of Plasmodium falciparum (PfDHODH) revealed high activity of some anti-isomers of the methyl esters, while the corresponding carboxylic acids and carboxamides were not active. The most active representative, methyl (1S*,3S*,5R*)-1,5-dimethyl-7-oxo-3-phenyltetrahydro-1H,5H-pyrazolo[1,2-a]pyrazole-1-carboxylate (IC50 = 2.9 ±â€¯0.3 µM), also exhibited very high selectivity of the parasite enzyme vs. the human enzyme, PfDHODH/HsDHODH > 350. According to the molecular docking score, this high activity is explainable by synergic interactions of the methyl, phenyl and the CO2Me substituent with the hydrophobic pockets in the active site of the enzyme. The carboxylic acid and carboxamides derived from this compound did not inhibit PfDHODH.