This invention features a method for enhancing bone growth or inhibiting bone resportion. The method includes administering to a subject in need thereof a compound of the following formula: A is H, R, or each of Ar1, Ar2, and Ar3, independently, is phenyl, thienyl, furyl, or pyrrolyl; each of R1, R2, R3, R4, R5, and R6, independently, is H, halogen, R, C(O)OH, C(O)OR, C(O)SH, C(O)SR, C(O)NH2, C(O)NHR, C(O)NRR′, ROH, ROR′, RSH, RSR′, NHR, NRR′, RNHR′, or RNR′R″; or R1 and R2 together, R3 and R4 together, or R5 and R6 together are ORO; wherein each of R, R′, and R″, independently is C1˜C6 alkyl; and n is 1, 2, or 3.