Treatment of IX with a base followed by addition of an R5-LG, wherein LG is a leaving group such as a halide, mesylate, triflate or a tosylate, and subsequent deprotection of the benzyl group by hydrogenation employing, for example, H2 and Pd/C, would give the desired succinate X. An example of a general method whereby diesters of structure IX can be obtained from cyclic esters XXX is shown in Sch