The University of Arkansas sophomore was one of Oakland's two second-round picks, coming in at No. 74 overall.
Sanburn went 4-1 with a 2.43 ERA in 22 games, including four starts, for the Razorbacks, striking out 49 in 40 2/3 innings.
Oakland managed to sign 33 of its 43 picks, including each of the first five and 12 of the first 13. Third-round selection Kyle Twomey, a prep lefty, went unsigned.