合成路线1

Treatment of (XIII) with aqueous trifluoroacetic acid produced simultaneous ketal group hydrolysis and lactonization, yielding intermediate (XIV). Optionally, basic hydrolysis of the ester groups of (XIII) with LiOH produced the lithium carboxylate salt (XV). Lactonization of (XV) with HOAc in chloroform gave (XVI). The cyclic ketal group of (XVI) was then hydrolyzed with aqueous trifluoroacetic acid to produce the intermediate (XVII). Alternatively, (XVII) was also produced by simultaneous hydrolysis and cyclization of (XV) with aqueous trifluoroacetic acid or by basic hydrolysis of (XIV), followed by acidic treatment. Intermediate (XIX) was prepared by acetylation of (XVI) followed by acidic hydrolysis of the resulting ketal (XVIII).