Cyclization of recently reported linear phosphino dipeptide isostere inhibitors of BACE1 via side chain olefin metathesis yielded macrocyclic BACE1 inhibitors. The most potent compound II-P1 (IC50 of 47 nM) and the corresponding linear analog I were tested for serum stability. The approach led to three times prolonged half life serum stability of 44 min for the macrocyclic inhibitor II-P1 compared to the linear compound I.