D-Aspartic acid 4-methyl ester is a protected form of D-Aspartic acid (A790020). D-Aspartic acid is the unnatural isomer of L-Aspartic acid (A790024). D-Aspartic acid naturally occurs in human ovarian follicular fluid, and is thought to be linked to oocyte quality. It is also found in the white matter of human brains, more specifically in myelin proteins.