Asymmetric Total Syntheses of (−)-Jorumycin, (−)-Renieramycin G, 3-<i>e</i><i>pi</i>-Jorumycin, and 3-<i>e</i><i>pi</i>-Renieramycin G

The total synthesis of (−)-jorumycin (1) and (−)-renieramycin G (2) has been accomplished in 25 and 23 steps, respectively, from 5-benzyloxy-2,4-dimethoxy-3-methyl-benzyl alcohol. The synthesis features a substrate-tunable stereoselective intramolecular Pictet−Spengler-type reaction for the construction of the key pentacyclic core of both targets, bearing either the natural configuration or the epimeric configuration at C-3. With access to a C-3 epi-pentacyclic framework, 3-epi-jorumycin (32) and 3-epi-renieramycin G (34) were also successfully synthesized. Furthermore, preliminary biological evaluation of 3-epi-jorumycin (32), in addition to relevant synthetic intermediates, revealed that significant cytotoxicity had been retained in these compounds. Therefore, these early studies constitute the basis for a new structure activity relationship (SAR) investigation for this class of antitumor antibiotics.