Industrial chloroquine manufacturing was developed in the 1940s. There is an extensive description in this 1949 article from Industrial and Engineering Chemistry:

"Chloroquine Manufacture"

https://sci-hub.tw/10.1021/ie50472a002

I mention chloroquine specifically because

a) It looks like it was effective at a lower concentration than remdesivir, according to this Nature article.

b) It's a simpler molecule. High volume production started back during World War II.