at least 33 the abundance can also be a at least 67 and b 100 in another embodiment the present invention provides an isolated novel deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof wherein the abundance of deuterium in r 33 r 35 is at least 33 the abundance can also be a at least 67 and b 100 in another embodiment the present invention provides an isolated novel deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof wherein the abundance of deuterium in r 37 r 39 is at least 33 the abundance can also be a at least 67 and b 100 in another embodiment the present invention provides an isolated novel deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof wherein the abundance of deuterium in r 40 r 44 is at least 20 the abundance can also be a at least 40 b at least 60 c at least 80 and d 100 in another embodiment the present invention provides an isolated novel deuterium enriched compound of formula i or a pharmaceutically acceptable salt thereof wherein the abundance of deuterium in r 32 r 36 and r 45 r 52 is at least 10 the abundance can also be a at least 20 b at least 30 c at least 40 d at least 50 e.