摘要:
Various processes are disclosed for preparing protected epicatechin oligomers having (4β,8)-interflavan linkages. In one process, a tetra-O-protected epicatechin monomer or oligomer is coupled with a protected, C-4 activated epicatechin monomer in the presence of an acidic clay such as a mortmorillonite clay. In another process, a 5,7,3′,4′-benzyl protected or a 3 -acetyl-, 5,7,3′,4′-benzyl protected epicatechin or catechin monomer or oligomer is reacted with 3 -O-acetyl-4-[(2-benzothiazolyl)thio]-5,7,3′,4′-tetra-O-benzylepicatechin in the presence of silver tetrafluoroborate. In another process, two 5,7,3′,4′-benzyl protected epicatechin monomers activated with 2-(benzothiazolyl)thio groups at the C-4 positions are cross-coupled in the presence of silver tetrofluoroborate. A process is also disclosed for reacting an unprotected epicatechin or catechin monomer with 4-(benzylthio) epicatechin or catechin. The use of naturally-derived and synthetically-prepared procyanidin (4β,8)4-pentamers to treat cancer is also disclosed.
摘要:
Oligomeric procyanidins containing 4&agr;-linked epicatechin units are rare in nature and have hitherto not been accessible through stereoselective synthesis. Provided herein is the preparation of the prototypical dimer, epicatechin-4&agr;,8-epicatechin, by reaction of the protected 4-ketones with aryllithium reagents derived by halogen/metal exchange from the aryl bromides. Removal of the 4-hydroxyl group from the resulting tertiary benzylic alcohols is effected by tri-n-butyltin hydride and trifluoroacetic acid in a completely stereoselective manner, resulting in hydride delivery exclusively from the &bgr; face.
摘要:
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 (4β,8)4-pentamers to treat cancer is also disclosed.
摘要:
Oligomeric procyanidins containing 4α-linked epicatechin units are rare in nature and have hitherto not been accessible through stereoselective synthesis. Provided herein is the preparation of the prototypical dimer, epicatechin-4α,8-epicatechin, by reaction of the protected 4-ketones with aryllithium reagents derived by halogen/metal exchange from the aryl bromides. Removal of the 4-hydroxyl group from the resulting tertiary benzylic alcohols is effected by tri-n-butyltin hydride and trifluoroacetic acid in a completely stereoselective manner, resulting in hydride delivery exclusively from the β face.
摘要:
Various processes are disclosed for preparing protected epicatechin oligomers having (4β,8)-interflavan linkages. In one process, a tetra-O-protected epicatechin monomer or oligomer is coupled with a protected, C-4 activated epicatechin monomer in the presence of an acidic clay such as a mortmorillonite clay. In another process, a 5,7,3′,4′-benzyl protected or a 3-acetyl-, 5,7,3′,4′-benzyl protected epicatechin or catechin monomer or oligomer is reacted with 3-O-acetyl-4-[(2-benzothiazolyl)thio]-5,7,3′,4′-tetra-O-benzylepicatechin in the presence of silver tetrafluoroborate. In another process, two 5,7,3′,4′-benzyl protected epicatechin monomers activated with 2-(benzothiazolyl)thio groups at the C-4 positions are cross-coupled in the presence of silver tetrofluoroborate. A process is also disclosed for reacting an unprotected epicatechin or catechin monomer with 4-(benzylthio)epicatechin or catechin. The use of naturally-derived and synthetically-prepared procyanidin (4β,8)4-pentamers to treat cancer is also disclosed.
摘要:
Oligomeric procyanidins containing 4&agr;-linked epicatechin units are rare in nature and have hitherto not been accessible through stereoselective synthesis. Provided herein is the preparation of the prototypical dimer, epicatechin-4&agr;,8-epicatechin, by reaction of the protected 4-ketones with aryllithium reagents derived by halogen/metal exchange from the aryl bromides. Removal of the 4-hydroxyl group from the resulting tertiary benzylic alcohols is effected by tri-n-butyltin hydride and trifluoroacetic acid in a completely stereoselective manner, resulting in hydride delivery exclusively from the &bgr; face.
摘要:
Intermediates useful for the synthesis of huperzine A represented by the structures below, and methods for their synthesis, wherein: R1 is lower alkyl, benzyl, or substituted benzyl; X is a suitable leaving group; Y is an electron withdrawing group that can subsequently be converted into an amino group; one broken line is present as a carbon—carbon bond and the other broken line is absent, where the broken line forms an unconjugated carbon—carbon double bond, which double bond may be endocyclic whereby n is 3 or the double bond may be exocyclic whereby n is 2.