Epoxidation of a β-himachalene derivative (A) can be carried out using meta-chloroperoxybenzoic acid (m-CPBA). An oxygen atom is added to the double bond C9C10, during the process, producing the epoxides P1 and P2. DFT calculations at the B3LYP/6-31G(d) level were used to study, Theoretically, the mechanism and stereoselectivity of the epoxidation reaction of compound A with m-CPBA. The calculation of activation energies associated with both possible reaction pathways, indicated that this epoxidation reaction is exothermic and highly stereoselective, favoring the formation of product P1 which is in agreement with the experimental results. Additionally, the IRC calculation shows that this reaction occurs via a one-step mechanism. The products P1, P2, and the starting compound A were evaluated for their antidiabetic activity and their potential to inhibit alpha-amylase and alpha-glucosidase through molecular docking, molecular dynamics, and ADMET studies. The evaluation of these three compounds aimed to study the effect of epoxidation and stereoselectivity on their inhibitory activity against the two enzymes.