A compound for use in a method for stabilizing oxy-hemoglobin in the blood of a subject with sickle cell anemia comprising contacting blood with a therapeutically effective amount of a compound of formula I or a pharmaceutically acceptable salt thereof or a pharmaceutically acceptable composition comprising a compound of formula I or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier, wherein: W, X, Y and Z are each independently CH or N; D and D 1 are independently a bond or NR b; A is optionally substituted aryl or optionally substituted heteroaryl; L is a bond, -C -, -(CR c R c) m -, -OC -, -(CR c R c) m -OC -, -(CR c R c) m -C -, - NR b C -, or -NR b C - (wherein the point of the attachment to R 1 is on the left-hand side); R 1 is selected from the group consisting of alkyl, cycloalkyl, aryl, heteroaryl, and heterocyclyl; each of which is substituted with 0-5 occurrences of R d; each R 3 is independently selected from the group consisting of halo, haloalkyl, alkyl, hydroxyl and -OR a, or two adjacent R 3 taken together with the carbon atoms to which they are attached form an optionally substituted heterocyclyl; each R a is independently selected from the group consisting of alkyl, acyl, hydroxyalkyl and haloalkyl; each R b is independently selected from the group consisting of hydrogen and alkyl; each R c is independently selected from the group consisting of hydrogen, halo, alkyl, alkoxy and halo alkoxy or two R c taken together with the carbon atoms to which they are attached form an optionally substituted cycloalkyl; each R d is independently selected from the group consisting of halo, haloalkyl, haloalkoxy, alkyl, alkynyl, nitro, cyano, hydroxyl, -C R a, -OC R a, -C OR a, - SR a, -NR a R b and -OR a, or two R d taken together with the carbon atoms to which they are attached form an optionally substituted heterocyclyl; n is 0, 1, or 2; m is 1, 2 or 3; h is 0, 1, or 2; g is 0, 1 or 2. W, X, Y and Z are each independently CH or N; D and D 1 are independently a bond or NR b; A is optionally substituted aryl or optionally substituted heteroaryl; L is a bond, -C -, -(CR c R c) m -, -OC -, -(CR c R c) m -OC -, -(CR c R c) m -C -, - NR b C -, or -NR b C - (wherein the point of the attachment to R 1 is on the left-hand side); R 1 is selected from the group consisting of alkyl, cycloalkyl, aryl, heteroaryl, and heterocyclyl; each of which is substituted with 0-5 occurrences of R d; each R 3 is independently selected from the group consisting of halo, haloalkyl, alkyl, hydroxyl and -OR a, or two adjacent R 3 taken together with the carbon atoms to which they are attached form an optionally substituted heterocyclyl; each R a is independently selected from the group consisting of alkyl, acyl, hydroxyalkyl and haloalkyl; each R b is independently selected from the group consisting of hydrogen and alkyl; each R c is independently selected from the group consisting of hydrogen, halo, alkyl, alkoxy and halo alkoxy or two R c taken together with the carbon atoms to which they are attached form an optionally substituted cycloalkyl; each R d is independently selected from the group consisting of halo, haloalkyl, haloalkoxy, alkyl, alkynyl, nitro, cyano, hydroxyl, -C R a, -OC R a, -C OR a, - SR a, -NR a R b and -OR a, or two R d taken together with the carbon atoms to which they are attached form an optionally substituted heterocyclyl; n is 0, 1, or 2; m is 1, 2 or 3; h is 0, 1, or 2; g is 0, 1 or 2.