Blinded Treatment Phase:

Participants will receive tilpisertib fosmecarbil Dose A for up to 12 weeks. An efficacy assessment will be performed at Week 12.

• Participants who achieve clinical response will receive tilpisertib fosmecarbil Dose B for up to Week 52.

Non-responder Treatment Phase:

• Participants who do not achieve clinical response at Week 12 will discontinue the Blinded Treatment Phase and have the option to enter into the Non-responder Treatment Phase. Participants will receive tilpisertib fosmecarbil Dose A for another 12 weeks. An efficacy assessment will be performed at Week 12 of the Non-responder Treatment Phase. Participants who achieved clinical response will receive tilpisertib fosmecarbil Dose B for up to Week 52. Participants who do not achieve clinical response at Non-responder Treatment Phase Week 12 will discontinue study drug.

Blinded Treatment Phase:

Participants will receive tilpisertib fosmecarbil Dose B for up to 12 weeks. An efficacy assessment will be performed at Week 12.

• Participants who achieve clinical response will receive tilpisertib fosmecarbil Dose B for up to Week 52.

Non-responder Treatment Phase:

• Participants who do not achieve clinical response at Week 12 will discontinue the Blinded Treatment Phase and have the option to enter into the Non-responder Treatment Phase. Participants will receive tilpisertib fosmecarbil Dose B for another 12 weeks. An efficacy assessment will be performed at Week 12 of the Non-responder Treatment Phase. Participants who achieved clinical response will receive tilpisertib fosmecarbil Dose B for up to Week 52. Participants who do not achieve clinical response at Non-responder Treatment Phase Week 12 will discontinue study drug.

Tablets administered orally

Clinical Response is defined as a decrease from baseline of ≥ 2 points and at least 30% in 3 components of the modified Mayo Clinic Score, Stool Frequency, Rectal Bleeding, and Endoscopic Findings, in addition to a ≥ 1 point decrease from baseline in the Rectal Bleeding subscore or Rectal Bleeding subscore of ≤ 1. The modified Mayo Clinic Score is a scoring system for assessment of UC activity and is composed of subscores from endoscopy (range: 0 to 3, where 0 = normal or inactive disease and 3 = severe disease [spontaneous bleeding, ulceration]), rectal bleeding (range: 0 to 3, where 0 = no blood seen and 3 = blood alone passes), and stool frequency (range: 0 to 3, where 0 = normal number of stools and 3 = at least 5 or more stools more than normal). Total score for modified Mayo Clinic Score ranges from 0 to 9 (sum of all subscores), with higher scores indicating higher disease activity.

Clinical Remission is defined as a Stool Frequency subscore ≤ 1 and not greater than baseline, Rectal Bleeding subscore of 0, and Endoscopic Findings subscore ≤ 1 at Week 12. The modified Mayo Clinic Score is a scoring system for assessment of UC activity and is composed of subscores from endoscopy (range: 0 to 3, where 0 = normal or inactive disease and 3 = severe disease [spontaneous bleeding, ulceration]), rectal bleeding (range: 0 to 3, where 0 = no blood seen and 3 = blood alone passes), stool frequency (range: 0 to 3, where 0 = normal number of stools and 3 = at least 5 or more stools more than normal). Total score for modified Mayo Clinic Score ranges from 0 to 9 (sum of all subscores), with higher scores indicating higher disease activity.