DEUTERIUM-ENRICHED TAPENTADOL

1 . A deuterium-enriched compound of formula I or a pharmaceutically acceptable salt thereof:

wherein R 1 -R 23 are independently selected from H and D; and the abundance of deuterium in R 1 -R 23 is at least 4%.

2 . A deuterium-enriched compound of claim 1 , wherein the abundance of deuterium in R 1 -R 23 is selected from at least 4%, at least 9%, at least 13%, at least 17%, at least 22%, at least 26%, at least 30%, at least 35%, at least 39%, at least 43%, at least 48%, at least 52%, at least 57%, at least 61%, at least 65%, at least 70%, at least 74%, at least 78%, at least 83%, at least 87%, at least 91%, at least 96%, and 100%.

3 . A deuterium-enriched compound of claim 1 , wherein the abundance of deuterium in R 1 is selected from at least 100%.

4 . A deuterium-enriched compound of claim 1 , wherein the abundance of deuterium in R 2 -R 5 is selected from at least 25%, at least 50%, at least 75%, and 100%.

5 . A deuterium-enriched compound of claim 1 , wherein the abundance of deuterium in R6-R 17 is selected from at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, and 100%.

6 . A deuterium-enriched compound of claim 1 , wherein the abundance of deuterium in R 18 -R 23 is selected from at least 17%, at least 33%, at least 50%, at least 67%, at least 83%, and 100%.

7 . A deuterium-enriched compound of claim 1 , wherein the compound is selected from compounds 1-5 of Table 1.

8 . A deuterium-enriched compound of claim 1 , wherein the compound is selected from compounds 6-10 of Table 2.

9 . An isolated deuterium-enriched compound of formula I or a pharmaceutically acceptable salt thereof:

wherein R 1 -R 23 are independently selected from H and D; and the abundance of deuterium in R 1 -R 23 is at least 4%.

10 . An isolated deuterium-enriched compound of claim 9 , wherein the abundance of deuterium in R 1 -R 23 is selected from at least 4%, at least 9%, at least 13%, at least 17%, at least 22%, at least 26%, at least 30%, at least 35%, at least 39%, at least 43%, at least 48%, at least 52%, at least 57%, at least 61%, at least 65%, at least 70%, at least 74%, at least 78%, at least 83%, at least 87%, at least 91%, at least 96%, and 100%.

11 . An isolated deuterium-enriched compound of claim 9 , wherein the abundance of deuterium in R 1 is selected from at least 100%.

12 . An isolated deuterium-enriched compound of claim 9 , wherein the abundance of deuterium in R 2 -R 5 is selected from at least 25%, at least 50%, at least 75%, and 100%.

13 . An isolated deuterium-enriched compound of claim 9 , wherein the abundance of deuterium in R 6 -R 17 is selected from at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, and 100%.

14 . An isolated deuterium-enriched compound of claim 9 , wherein the compound is selected from compounds 1-5 of Table 1.

15 . An isolated deuterium-enriched compound of claim 9 , wherein the compound is selected from compounds 6-10 of Table 2.

16 . A mixture of deuterium-enriched compounds of formula I or a pharmaceutically acceptable salt thereof:

wherein R 1 -R 23 are independently selected from H and D; and the abundance of deuterium in R 1 -R 23 is at least 4%.

17 . A mixture of deuterium-enriched compound of claim 16 , wherein the compound is selected from compounds 1-5 of Table 1.

18 . A mixture of deuterium-enriched compound of claim 16 , wherein the compound is selected from compounds 6-10 of Table 2.

19 . A pharmaceutical composition, comprising: a pharmaceutically acceptable carrier and a therapeutically effective amount of a compound of claim 1 or a pharmaceutically acceptable salt form thereof.

20 . A method for treating pain comprising: administering, to a patient in need thereof, a therapeutically effective amount of a compound of claim 1 or a pharmaceutically acceptable salt form thereof.