Nucleoside/nucleobase chemical synthesis I'm interested in the chemical synthesis of nucleoside phosphoramidites, but all the procedures I can find have "start with a protected nucleoside" as the first step. Searches for chemical synthesis of nucleosides all seem to find process that start with existing nucleobases, or in vivo processes, or speculative origin-of-life processes. Searching for chemical synthesis of nucleobases ONLY seems to find speculative origin-of-life processes.

What I'm looking for (just out of curiosity) are processes for chemical synthesis of nucleosides from a non-biological basis (not using pre-existing nucleobases) as used in typical commercial/industrial supply of nucleoside phosphoramidites. I'm starting to wonder if they even are chemically synthesized, or if they are instead harvested in some way, but it's hard to find a smoking gun that outright says it one way or the other without access to whitepapers anymore (no more university account).

Does anybody know?
Finally found what I was looking for, especially paired with Mithoron's comments.

"Currently, purine nucleotides are obtained at industrial level mainly by microbial fermentation".

https://microbialcellfactories.biomedcentral.com/articles/10.1186/s12934-015-0234-4

Ledesma-Amaro, Rodrigo &amp; Jiménez, Alberto &amp; Santos, María de los Ángeles &amp; Revuelta, José. (2013). Biotechnological production of feed nucleotides by microbial strain improvement. Process Biochemistry. 48. 1263-1270. 10.1016/j.procbio.2013.06.025.