Brightest cluster galaxies ( BCGs ) are excellent laboratories to study galaxy evolution in dense Mpc-scale environments . We have observed in CO ( 1 \rightarrow 0 ) , CO ( 2 \rightarrow 1 ) , CO ( 3 \rightarrow 2 ) , or CO ( 4 \rightarrow 3 ) , with the IRAM-30m , 18 BCGs at z \sim 0.2 - 0.9 that are drawn from the Cluster Lensing And Supernova survey with Hubble ( CLASH ) survey . Our sample includes RX1532 , which is our primary target , being among the BCGs with the highest star formation rate ( SFR \gtrsim 100 ~ { } M _ { \odot } /yr ) in the CLASH sample . We unambiguously detected both CO ( 1 \rightarrow 0 ) and CO ( 3 \rightarrow 2 ) in RX1532 , yielding a large reservoir of molecular gas , M _ { H _ { 2 } } = ( 8.7 \pm 1.1 ) \times 10 ^ { 10 } ~ { } M _ { \odot } , and a high level of excitation r _ { 31 } = 0.75 \pm 0.12 . A morphological analysis of the Hubble Space Telescope I-band image of RX1532 reveals the presence of clumpy substructures both within and outside the half-light radius r _ { e } = ( 11.6 \pm 0.3 ) kpc , similarly to those found independently both in ultraviolet and in H _ { \alpha } in previous work . We tentatively detected CO ( 1 \rightarrow 0 ) or CO ( 2 \rightarrow 1 ) in four other BCGs , with molecular gas reservoirs in the range M _ { H _ { 2 } } = 2 \times 10 ^ { 10 - 11 } ~ { } M _ { \odot } . For the remaining 13 BCGs we set robust upper limits of M _ { H _ { 2 } } / M _ { \star } \lesssim 0.1 , which are among the lowest molecular gas to stellar mass ratios found for distant ellipticals and BCGs . By comparison with distant cluster galaxies observed in CO our study shows that RX1532 ( M _ { H _ { 2 } } / M _ { \star } = 0.40 \pm 0.05 ) belongs to the rare population of star forming and gas-rich BCGs in the distant universe . By using available X-ray based estimates of the central intra-cluster medium entropy , we show that the detection of large reservoirs of molecular gas M _ { H _ { 2 } } \gtrsim 10 ^ { 10 } ~ { } M _ { \odot } in distant BCGs is possible when the two conditions are met : i ) high SFR and ii ) low central entropy , which favors the condensation and the inflow of gas onto the BCGs themselves , similarly to what has been previously found for some local BCGs .