Stereoselective and Divergent Aza-Adenosine and Aza-Guanosine Syntheses from Xylofuranose, the Key Fragments of a STING Cyclic Dinucleotide Agonist

Abstract

The stereoselective and divergent synthesis of two aza-nucleosides is reported. Starting from xylofuranose 9, aza-adenosine 2 was prepared in 13 steps and 7% overall yield, and aza-guanosine 3 was prepared in 13 steps and 7.8% overall yield. Compared to the original syntheses, some advantages of these new routes are significant yield improvement, overall step-count reduction, an optimized protecting group strategy, the development of a versatile platform for nitrogenous base incorporation, and the elimination of hazardous reagents (e.g., benzyl isocyanate, Et3N·HF).

P(III) vs P(V): A P(V) Reagent for Thiophosphoramidate Linkages and Application to an Asymmetric Synthesis of a Cyclic Dinucleotide STING Agonist

“…The previous route began with the 3-aza-nucleoside 2 and employed standard P­(III) phosphoramidite chemistry (Scheme ), which was successful for producing small quantities of 1 . However, we discovered crippling challenges in using this route to deliver material to enable the study of the clinical efficacy of 1 , all of which stemmed from the introduction of the chiral thiophos­phoramidate.…”