Patent ID: 8716333

Claim:
A compound of the formula III: wherein R 1 is CO 2 Et or a functional group that can be converted to CO 2 Et selected from aryl esters, heteroaryl esters, lower alkyl esters, higher alkyl esters, thio esters, allyl esters, propargyl esters, C(O)H, C(O)OH, C(O)O − , CCl 3 , CN, C≡CH, CH 2 C≡CH, CH 2 OH and alkyl ethers thereof, vinyl, C(O-alkyl) 3 , amides, alkyl amides, aryl amides, heteroaryl amides, thioesters and heterocycles; R 2 and R 3 are independently selected from H and a suitable protecting group, or R 2 and R 3 are joined to form a suitable protecting group; and R 4a and R 4b are independently selected from H and a suitable protecting group or R 4a and R 4b are joined to form a suitable protecting group; wherein, one or more available hydrogens in R 1 , R 2 , R 3 , R 4a and/or R 4b is/are optionally replaced with F and/or one or more of available atoms is/are optionally replaced with an isotopic label, or a salt and/or solvate thereof.