Heterocyclic compounds

A compound of formula (I):

• wherein:
• X is selected from the group consisting of O and NR1;
• R1 is selected from the group consisting of hydrogen and a nitrogen protecting group;
• R2 is selected from the group consisting of —C(O)O—, —C(O)—, —O—, —NR4— and —CR52—;
• each R3 is independently selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclyl, aryl, heteroaryl and cyano, any of which is optionally substituted;
• R4 is selected from the group consisting of hydrogen, alkyl, and a nitrogen protecting group;
• and
• each R5 is independently selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclyl, aryl, heteroaryl, acyl, alkoxy, amido, amino, carboxy, cyano, ester, halo, haloalkyl, hydroxy, nitro, phosphonate, sulfinyl, sulfonyl, sulfonate, sulfonamino and sulfonamido, any of which is optionally substituted;
• or two R5 are taken together with the atom to which they are attached to form an optionally substituted ring system.