(1 1). Hydrazinolysis of 11 gave l-amino-4-[p-(carbomethoxy) phenoxy]-2-butanone oxime (4), which was used as the key intermediate for the construction of 11-oxahomofolic acid (2) by modifcations of the Boon and Leigh procedure. The dithionite reduction product of 2, 7, 8- dihydro-ll-oxahomofolic acid, served as a substrate of Lactobacillus casei dihydrofolate reductase and exhibited a relative rate of 50% of the natural substrate under identical ...