A compound of formula (1): wherein R1, R2, R3 and Y are as defined herein, or a pharmaceutically-acceptable and -cleavable ester, or acid addition salt thereof, useful for promoting the release of parathyroid hormone, e.g. for preventing or treating bone conditions which are associated with increased calcium depletion or resorption or in which stimulation of bone formation and calcium fixation in the bone is desirable.