Compounds and their uses as CD38 inhibitors

A compound of formula I:

• or a pharmaceutically acceptable salt thereof, wherein:
• A1 is
• wherein A1 is optionally substituted with 0, 1 or 2 substituents independently selected from methyl and trifluoromethyl;
• A2 is
• wherein A2 is optionally substituted with 0 or 1 substituent selected from —CN, methyl, isopropyl, trifluoromethyl, methoxy, cyclobutoxy, oxetan-3-yloxy, —NH2, —NHCH3, and —N(CH3)2;
• A3 is
• wherein A3 is optionally substituted with 0, 1 or 2 substituents independently selected from —CN, —OCH2CH2OCH3, —COCH3, —F, —Cl, methyl, trifluoromethyl, hydroxyethoxy, carboxymethoxy, hydroxy, and methoxy;
• and
• R is H or C1-6 alkyl.