Inhibitors of dihydroceramide desaturase for treating disease

A compound of Formula I:

• or a salt thereof, wherein:
• R1a and R1b are independently selected from hydrogen, cycloalkylalkyl, aryl, and heteroaryl, and is optionally substituted with 1, 2, or 3 R2 groups, or
• R1a and R1b, together with the intervening atoms, form a 5-7 membered heterocyclic ring, and is optionally substituted with 1, 2, or 3 R2 groups;
• at least one of R1a and R1b is not hydrogen;
• X is selected from ethenyl, alkyl, aryl, biaryl, (aryl)cycloalkyl, (aryl)heterocycloalkyl, (aryl)heteroaryl, cycloalkyl, (cycloalkyl)aryl, (cycloalkyl)cycloalkyl, (cycloalkyl)heterocycloalkyl, (cycloalkyl)heteroaryl, heterocycloalkyl, (hetercycloalkyl)aryl, (heterocycloalkyl)cycloalkyl, (heterocycloalkyl)heteroaryl, (heterocycloalkyl)heterocycloalkyl, heteroaryl, (heteroaryl)aryl, (heteroaryl)cycloalkyl, (heteroaryl)heterocycloalkyl, and(heteroaryl)heteroaryl, any of which is optionally substituted with 1, 2, 3, or 4 R3 groups;
• Y is selected from —CHR4—, —CHR4CHR4—, and —CR4═CR4;
• each R2 is independently selected from alkyl, alkoxy, amino, cycloalkyl, heterocycloalkyl, (heterocycloalkyl)alkyl, halogen, hydroxy, S-sulfonamido, and oxo, and is optionally substituted with 1, 2, or 3 R5
• n is selected from 1, 2, 3, 4, and 5;
• each R3 is independently selected from alkyl, alkoxy, cyano, haloalkyl, hydroxy, halogen, and oxo;
• and
• each R4 is independently selected from hydrogen, alkyl, alkylamino, halo, and hydroxyl;
• and
• each R5 is independently selected from hydroxy and alkoxy.