Crystalline forms of (S)-2-ethylbutyl 2-(((S)-(((2R,3S,4R,5R)-5-(4-aminopyrrolo[2,1-f] [1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl)methoxy) (phenoxy) phosphoryl)amino)propanoate

1. A crystalline form selected from the group consisting of:

(S)-2-Ethylbutyl 2-(((S)-(((2R,3S,4R,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl)methoxy)(phenoxy)phosphoryl)amino)propanoate characterized by an X-ray powder diffraction (XRPD) pattern comprising degree 2θ-reflections (±0.2° 2θ) at 5.3°, 20.6°, and 22.7°;

(S)-2-Ethylbutyl 2-(((S)-(((2R,3S,4R,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl)methoxy)(phenoxy)phosphoryl)amino)propanoate characterized by an X-ray powder diffraction (XRPD) pattern comprising degree 2θ-reflections (±0.2° 2θ) at 4.1°, 8.2°, 17.1°, and 23.8°;

(S)-2-Ethylbutyl 2-(((S)-(((2R,3S,4R,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl)methoxy)(phenoxy)phosphoryl)amino)propanoate characterized by an X-ray powder diffraction (XRPD) pattern comprising degree 2θ-reflections (±0.2° 2θ) at 22.6°, 19.9°, and 14.1°;

(S)-2-Ethylbutyl 2-(((S)-(((2R,3S,4R,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl)methoxy)(phenoxy)phosphoryl)amino)propanoate characterized by an X-ray powder diffraction (XRPD) pattern comprising degree 2θ-reflections (±0.2° 2θ) at 15.9°, 22.6°, and 14.1°;

(S)-2-Ethylbutyl 2-(((S)-(((2R,3S,4R,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl)methoxy)(phenoxy)phosphoryl)amino)propanoate characterized by an X-ray powder diffraction (XRPD) pattern comprising degree 2θ-reflections (±0.2° 2θ) at 16.1°, 22.4°, and 12.7°;

(S)-2-Ethylbutyl 2-(((S)-(((2R,3 S,4R,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl)methoxy)(phenoxy)phosphoryl)amino)propanoate characterized by an X-ray powder diffraction (XRPD) pattern comprising degree 2θ-reflections (±0.2° 2θ) at 16.7°, 12.6°, and 17.2°; and

(S)-2-Ethylbutyl 2-(((S)-(((2R,3 S,4R,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl)methoxy)(phenoxy)phosphoryl)amino)propanoate maleate Form I characterized by an X-ray powder diffraction (XRPD) pattern comprising degree 2θ-reflections (±0.2° 2θ) at 16.3°, 4.6°, and 9.0°.

2. The crystalline form of claim 1 , wherein the crystalline form is characterized by an X-ray powder diffraction (XRPD) pattern comprising degree 2θ-reflections (±0.2° 2θ) at 5.3°, 20.6°, and 22.7°.

3. The crystalline form of claim 2 , wherein the X-ray powder diffraction (XRPD) pattern further comprises degree 2θ-reflections (±0.2° 2θ) at 17.1° and 20.0°.

4. The crystalline form of claim 2 , characterized by an X-ray powder diffraction (XRPD) pattern substantially as set forth in FIG. 1 .

5. The crystalline form of claim 2 , characterized by differential scanning calorimetry (DSC) pattern substantially as set forth in FIG. 2 .

6. The crystalline form of claim 2 , characterized by thermogravimetric analysis (TGA) pattern substantially as set forth in FIG. 3 .

7. The crystalline form of claim 2 , characterized by a dynamic vapor sorption (DVS) pattern substantially as set forth in FIG. 4 .

8. The crystalline form of claim 1 , wherein the crystalline form is characterized by an X-ray powder diffraction (XRPD) pattern comprising degree 2θ-reflections (±0.2° 2θ) at 4.1°, 8.2°, 17.1°, and 23.8°.

9. The crystalline form of claim 1 , wherein the crystalline form is characterized by an X-ray powder diffraction (XRPD) pattern comprising degree 2θ-reflections (±0.2° 2θ) at 22.6°, 19.9°, and 14.1°.

10. The crystalline form of claim 9 , wherein the X-ray powder diffraction (XRPD) pattern further comprises degree 2θ-reflections (±0.2° 2θ) 17.4°, 7.9° and 12.5°.

11. The crystalline form of claim 9 , characterized by an X-ray powder diffraction (XRPD) pattern substantially as set forth in FIG. 10 .

12. The crystalline form of claim 9 , characterized by differential scanning calorimetry (DSC) pattern substantially as set forth in FIG. 11 .

13. The crystalline form of claim 9 , characterized by thermogravimetric analysis (TGA) pattern substantially as set forth in FIG. 12 .

14. The crystalline form of claim 1 wherein the crystalline form is characterized by an X-ray powder diffraction (XRPD) pattern comprising degree 2θ-reflections (±0.2° 2θ) at 15.9°, 22.6°, and 14.1°.

15. The crystalline form of claim 14 , wherein the X-ray powder diffraction (XRPD) pattern further comprises degree 2θ-reflections (±0.2° 2θ) at 12.5° 2 0±0.2° 2 0.

16. The crystalline form of claim 14 , characterized by an X-ray powder diffraction (XRPD) pattern substantially as set forth in FIG. 13 .

17. The crystalline form of claim 14 , characterized by differential scanning calorimetry (DSC) pattern substantially as set forth in FIG. 14 .

18. The crystalline form of claim 14 , characterized by thermogravimetric analysis (TGA) pattern substantially as set forth in FIG. 15 .

19. The crystalline form of claim 1 wherein the crystalline form is characterized by an X-ray powder diffraction (XRPD) pattern comprising degree 2θ-reflections (±0.2° 2θ) at 16.1°, 22.4°, and 12.7°.

20. The crystalline form of claim 19 , wherein the X-ray powder diffraction (XRPD) pattern further comprises degree 2θ-reflections (±0.2° 2θ) 13.9°, 24.2°, and 17.5°.

21. The crystalline form of claim 19 , characterized by an X-ray powder diffraction (XRPD) pattern substantially as set forth in FIG. 16 .

22. The crystalline form of claim 19 , characterized by differential scanning calorimetry (DSC) pattern substantially as set forth in FIG. 17 .

23. The mixture of crystalline form of claim 19 , characterized by thermogravimetric analysis (TGA) pattern substantially as set forth in FIG. 18 .

24. The crystalline form of claim 1 wherein the crystalline form is characterized by an X-ray powder diffraction (XRPD) pattern comprising degree 2θ-reflections (±0.2° 2θ) at 16.7°, 12.6°, and 17.2°.

25. The crystalline form of claim 24 , wherein the X-ray powder diffraction (XRPD) pattern further comprises degree 2θ-reflections (±0.2° 2θ) at 19.6° and 14.1°.

26. The crystalline form of claim 24 , characterized by an X-ray powder diffraction (XRPD) pattern substantially as set forth in FIG. 19 .

27. The crystalline form of claim 24 , characterized by differential scanning calorimetry (DSC) pattern substantially as set forth in FIG. 20 .

28. The crystalline form of claim 24 , characterized by thermogravimetric analysis (TGA) pattern substantially as set forth in FIG. 21 .

29. The crystalline form of claim 1 , wherein the crystalline form is characterized by an X-ray powder diffraction (XRPD) pattern comprising degree 2θ-reflections (±0.2° 2θ) at 16.3°, 4.6°, and 9.0°.

30. The crystalline form of claim 29 , wherein the X-ray powder diffraction (XRPD) pattern further comprises degree 2θ-reflections (±0.2° 2θ) at 6.2° and 7.3°.

31. The crystalline form of claim 29 , characterized by an X-ray powder diffraction (XRPD) pattern substantially as set forth in FIG. 22 .

32. The crystalline form of claim 29 , characterized by differential scanning calorimetry (DSC) pattern substantially as set forth in FIG. 23 .

33. The crystalline form of claim 29 , characterized by thermogravimetric analysis (TGA) pattern substantially as set forth in FIG. 24 .

34. The crystalline form of claim 29 , characterized by a dynamic vapor sorption (DVS) pattern substantially as set forth in FIG. 25 .

35. A pharmaceutical composition comprising a crystalline form of claim 1 and a pharmaceutically acceptable excipient.

36. The pharmaceutical composition of claim 35 , further comprising one to three additional therapeutic agents.

37. The pharmaceutical composition of claim 36 , wherein the additional therapeutic agents are each active against a virus selected from the group consisting of Arenaviridae, Coronaviridae, Filoviridae, Flaviviridae, and Paramyxoviridae.

38. The pharmaceutical composition of claim 35 , wherein the pharmaceutical composition is in a unit dosage form.

39. The pharmaceutical composition of claim 38 , wherein the unit dosage form is a solution.

40. A pharmaceutical composition prepared by combining a therapeutically effective amount of a crystalline form of claim 1 with a pharmaceutically acceptable excipient.

41. A method for treating a virus infection in a human in need thereof, the method comprising administering to the human a therapeutically effective amount of a crystalline form of claim 1 .

42. The method for treating a virus infection in a human of claim 41 wherein the virus infection is caused by a virus selected from the group consisting of Arenaviridae, Coronaviridae, Filoviridae, Flaviviridae, and Paramyxoviridae.

43. A method of preparing a crystalline form of (S)-2-ethylbutyl 2-(((S)-(((2R,3S,4R,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-cyano-3,4-dihydroxytetrahydrofuran-2-yl)methoxy)(phenoxy)phosphoryl)amino)propanoate (Formula I) characterized by an X-ray powder diffraction (XRPD) pattern comprising degree 2θ-reflections (±0.2° 2θ) at 22.3°, 16.9°, and 16.2°, comprising

Contacting the Formula I and a solvent mixture comprising isopropanol and water, wherein the Formula I remains substantially insoluble in the solvent mixture, thereby preparing the crystalline form.

44. The crystalline form of claim 8 , characterized by a unit cell as determined by single crystal X-ray crystallography of the following dimensions: a=10.5800 (4) Å; b=7.4526 (4) Å; c=21.5691 (12) Å; α=90°; β=92.500 (3)°; and γ=90°.