The present invention relates to compounds having the general Formula (I) with the definitions of X, Y, R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.9, and R.sub.10 given below, and/or a salt or ester thereof. Furthermore the invention relates to the use of said compounds for the treatment of Alzheimer's disease and their use for the modulation of .gamma.-secretase activity.