I. Ojima et al., Macrocycle formation by ring-closing metathesis. Application to the syntheses of novel macrocyclic taxoids, J AM CHEM S, 122(22), 2000, pp. 5343-5353
A series of novel macrocyclic taxoids 6 and 6' bearing 16-, 17-, and 18-mem
bered rings connecting the substituents at the C-2 and C-3' positions were
designed and synthesized. The syntheses of these macrocycles 6 and 6' were
accomplished using the highly efficient ruthenium-catalyzed ring-closing me
tathesis (RCM) of taxoid-omega,omega'-dienes 7 in the key step. Taxoid-omeg
a,omega'-dienes 7 were obtained through the ring-opening coupling of 4-alke
nyl-beta-lactams 9 with 2-alkenoylbaccatins 8 in good to high yields. Altho
ugh various novel pentacyclic macrocycles 6 and 6' were successfully synthe
sized, there were cases in which the desired RCM did not proceed. The scope
and limitation of RCM in its application to highly functionalized complex
substrates are discussed. All macrocyclic taxoids 6 and 6' were found to be
cytotoxic, with some of them exhibiting submicromolar IC50 values against
a human breast cancer cell line.