Various processes are disclosed for preparing procyanidin oligomers having (4,8)-interflavan linkages. In an improved process, a tetra-O-protected-epicatechin or -catechin monomer or oligomer is coupled with a protected, C-4 alkoxy-activated-epicatechin or -catechin monomer in the presence of an acidic clay instead of a Lewis acid. In a second process, a 5,7,3',4'-tetra-O-protected or preferably penta-O-protected-epicatechin or -catechin monomer or oligomer is reacted with a tetra-O-protected or preferably penta-O-protected-epicatechin or -catechin monomer having a thio activating group at the C-4 position; the coupling is carried out in the presence of silver tetrafluoroborate. In third process, two molecules of a penta-O-protected-epicatechin or -catechin monomer activated with a 2-(benzothiazolyl)thio group at the C-4 position are self-condensed in the presence of silver tetrafluoroborate. An improved two-step process for preparing a C-4 alkoxy activated tetra-O-benzyl-protected, 8-bromo-blocked-epicatechin or -catechin monomer is also provided. The use of naturally-derived and synthetically-prepared procyanidin (4.beta.,8).sub.4-pentamers to treat cancer is also disclosed.
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to PCT/US03/31375, filed Oct. 2, 2003, which is a continuation in part of Ser. No. 10/658,241 filed Sep. 9, 2003, now U.S. Pat. No. 7,067,679, which is a utility application based on provisional application Ser. No. 60/415,616 filed Oct. 2, 2002.
