Synthesis of 4-hydroxymethyl-2,4-methanoproline

3-Oxabicyclo[3.1.1]heptanes as Isosteres of meta-Substituted Benzene Rings

Replacement of the aromatic rings in drug candidates with isosteric rigid sp3-rich scaffolds can improve physicochemical properties, increase the chance of progressing the molecule in development, and open new chemical space. Isosteres of meta-substituted benzenes remain challenging due to the difficulty of mimicking the exit vector angles and bond distances. Herein, we report the synthesis of 1,5-disubstituted 3-oxabicyclo[3.1.1]heptanes (oxa-BCHeps), which can serve as saturated isosteres of meta-substituted phenyl rings with a similar geometric arrangement. This structural motif can be obtained under mild reaction conditions via acid-mediated isomerization of (2-oxaspiro[3.3]heptan-6-yl)methanols using catalytic quantities of pyridinium chloride (PyrHCl). We demonstrate the utility of this methodology by preparing various building blocks for use in medicinal chemistry and incorporating 3-oxa-BCHep into the anticancer drug sonidegib, improving its physicochemical properties, such as permeability, metabolic stability, and solubility.

Stereoselective Construction of Methylenecyclobutane-Fused Indolines through Photosensitized [2+2] Cycloaddition of Allene-Tethered Indole Derivatives

Irradiation of 1-(hexa-4,5-dienoyl)indole derivatives in the presence of an aromatic ketone by a high-pressure mercury lamp through Pyrex glass gave the corresponding cyclized products stereoselectively in high yields. The major part of the products was an all- cis-fused methylenecyclobutane-type compound produced through [2+2] cycloaddition, accompanied by small amounts of alkynes via 1,5-hydrogen transfer of a biradical intermediate. Among a range of aromatic ketones, 3',4'-dimethoxyacetophenone was found to sensitize the substrate quite effectively.

Photochemical In-Flow Synthesis of 2,4-Methanopyrrolidines: Pyrrolidine Analogues with Improved Water Solubility and Reduced Lipophilicity

A practical synthesis of 2,4-methanopyrrolidines was elaborated. The key synthetic step was an intramolecular photochemical [2 + 2]-cycloaddition of an acrylic acid derivative in flow. In spite of a higher molecular weight, 2,4-methanopyrrolidines were shown to have higher solubility in water and lower lipophilicity than pyrrolidines, important characteristics of bioactive molecules in drug design.