COMPOUNDS FOR REDUCING THE VISCOSITY OF BIOLOGICAL FORMULATIONS

1 . A compound of Formula I:

or a pharmaceutically acceptable salt thereof,

wherein:

X is

R 1 is H or methyl;

R 2 is H or

R 3A and R 3B are each H or together form oxo;

R 4A and R 4B are each H or together form oxo;

R 5 is H or methyl; and

each occurrence of n is independently 1 to 5;

and wherein indicates the point of attachment to the rest of the compound.

2 . The compound of claim 1 , or a pharmaceutically acceptable salt thereof, wherein R 2 is H.

3 . The compound of claim 1 , or a pharmaceutically acceptable salt thereof, wherein R 2 is

4 . The compound of claim 3 , or a pharmaceutically acceptable salt thereof, wherein R 2 is

5 . The compound of claim 1 , or a pharmaceutically acceptable salt thereof, wherein R 1 is methyl.

6 . The compound of claim 5 , or a pharmaceutically acceptable salt thereof, wherein R 3A and R 3B are H.

7 . The compound of claim 5 , or a pharmaceutically acceptable salt thereof, wherein R 3A and R 3B join to form oxo.

8 . The compound of claim 1 , wherein each occurrence of n is independently 1 to 3.

9 . A compound of claim 1 having the structure:

or a pharmaceutically acceptable salt thereof.

10 . A pharmaceutical composition comprising an active biological ingredient (ABI) and the compound of claim 1 , or a pharmaceutically acceptable salt thereof, wherein the ABI is an antibody or antigen binding fragment thereof or a therapeutic protein.

11 . The pharmaceutical composition of claim 10 , wherein the ABI is an antibody or antigen binding fragment thereof, present in a concentration of about 50-250 mg/mL.

12 . The pharmaceutical composition according to claim 10 , further comprising histidine buffer at about pH 5.0 to about pH 6.0 in a concentration of about 5 mM to about 20 mM.

13 . The pharmaceutical composition according to claim 12 , which further comprises about 0.01% to about 0.04% w/v non-ionic surfactant.

14 . (canceled)

15 . (canceled)

16 . The pharmaceutical composition according to claim 13 , further comprising a stabilizer.

17 . (canceled)

18 . (canceled)

19 . The pharmaceutical composition according to claim 10 , wherein the ABI is an anti-PD-1 antibody or antigen binding fragment thereof that specifically binds human programmed death receptor 1 (PD-1).

20 . (canceled)

21 . (canceled)

22 . (canceled)

23 . (canceled)

24 . The pharmaceutical composition of claim 19 , wherein the antibody or antigen binding fragment thereof is present at a concentration of 100-250 mg/mL and wherein the composition comprises 10 mM histidine, 7% sucrose, and 0.02% polysorbate 80.

25 . (canceled)

26 . The pharmaceutical composition of claim 10 , further comprising a second ABI.

27 . A pharmaceutical composition comprising from 100 to 200 mg/mL pembrolizumab, 10 mM histidine buffer and the compound of claim 1 , or a pharmaceutically acceptable salt thereof.

28 . (canceled)

29 . A method for lowering the viscosity of a pharmaceutical formulation comprising:

(a) providing a pharmaceutical formulation comprising an ABI at a concentration of about 50 mg/mL to about 250 mg/mL, wherein the formulation is in aqueous solution; and

(b) adding a compound according to claim 1 to the solution;

wherein the viscosity of the pharmaceutical formulation following addition of the compound is ≤25 mPa-S.

30 . A method for treating a disease or pathological condition comprising administering to a subject in need of such treatment a therapeutically effective amount of a pharmaceutical composition according to claim 10 .

31 . (canceled)

32 . (canceled)