Biomimetic syntheses and antiproliferative activities of racemic, natural (-), and unnnatural (+) glyceollin I.

A 14-step biomimetic synthetic route to glyceollin I (1.5% overall yield) was developed and deployed to produce the natural enantiomeric form in soy, its unnatural stereoisomer, and a racemic mixture. Enantiomeric excess was assessed by asymmetric NMR shift reagents and chiral HPLC. Antiproliferative effects were measured in human breast, ovarian, and prostate cancer cell lines, with all three chiral forms exhibiting growth inhibition (GI) in the low to mid µM range for all cells. The natural enantiomer, and in some cases the racemate, gave significantly greater GI than the unnatural stereoisomer for estrogen receptor positive (ER(+)) versus ER(-) breast/ovarian cell lines as well as for androgen receptor positive (AR(+)) versus AR(-) prostate cancer cells. Surprisingly, differences between ER(+) and ER(-) cell lines were not altered by media estrogen conditions. These results suggest the antiproliferative mechanism of glyceollin I stereoisomers may be more complicated than strictly ER interactions.

Glyceollin I enantiomers distinctly regulate ER-mediated gene expression.

Glyceollins are pterocarpan phytoalexins elicited in high concentrations when soybeans are stressed. We have previously reported that the three glyceollin isomers (GLY I-III) exhibit antiestrogenic properties, which may have significant biological effects upon human exposure. Of the three isomers, we have recently shown that glyceollin I is the most potent antiestrogen. Natural (-)-glyceollin I recently was synthesized along with its racemate and unnatural (+) enantiomer. In this study, we compared the glyceollin I enantiomers' ER binding affinity, ability to inhibit estrogen responsive element transcriptional (ERE) activity and endogenous gene expression in MCF-7 cells. The results demonstrated similar binding affinities for both ERalpha and ERbeta. Reporter gene assays in MCF-7 cells revealed that while (+)-glyceollin I slightly stimulated ERE transcriptional activity, (-)-glyceollin I decreased activity induced by estrogen. Co-transfection reporter assays performed in HEK 293 cells demonstrated that (+)-glyceollin I increased ERE transcriptional activity of ERalpha and ERbeta with and without estrogen with no antiestrogenic activity observed. Conversely, (-)-glyceollin I decreased the activity of both ER subtypes stimulated by estradiol demonstrating potent antiestrogenic properties. Additionally, each Gly I enantiomer induced unique gene expression profiles in a PCR array panel of genes commonly altered in breast cancer.

Total syntheses of racemic and natural glycinol.

Total syntheses of racemic and (-)-glycinol (1) are described. A Wittig reaction produced the isoflav-3-ene from which a Sharpless dihydroxylation introduced either the racemic or enantiomeric 6a-hydroxy group. A 5.5% overall yield of racemic material was obtained after 12 steps. A method was devised for a one-pot switch of protecting groups masking a sensitive resorcinolic para-functionality, and conditions were optimized to prompt spontaneous closure of the pterocarpanolic dihydrofuran upon subsequent exposure of its ortho-functionality. These improvements eliminated two steps and increased the overall yield to 9.8% during production of the natural enantiomer.

Total syntheses of racemic, natural (-) and unnatural (+) glyceollin I.

The first total syntheses of racemic glyceollin I and its enantiomers are described. A Wittig approach was utilized as an entry to the appropriately substituted isoflav-3-ene so that an osmium tetroxide mediated asymmetric dihydroxylation could be deployed for stereospecific introduction of the 6a-hydroxy group. While using triphenylphosphine hydrobromide, a novel method was found for gently removing MOM from protected phenolic hydroxyl groups present within sensitive systems.

Practical synthesis of lespedezol A1.

A practical formal synthesis of lespedezol A 1 ( 1) was accomplished in 33% yield for four steps starting from formation of the substituted chalcone. Of particular note is a useful protocol for reduction of the 2-ene bond in the isoflavone intermediate. A significant improvement in the final ring closure when water was scavenged from the reaction is also noteworthy. The ready availability of lespedezol A 1 will provide material for further pharmacological evaluation and for exploration of the pterocarpene nucleus as a potential entry into various 6a-hydroxypterocarpans.

Total synthesis of xanthohumol.

The total synthesis of xanthohumol (1) was accomplished in 10% overall yield from phloracetophenone after six steps. Insertion of a prenyl group onto the aryl ring was achieved by a para-Claisen rearrangement after using a Mitsunobu reaction to establish the key prenyl ether precursor. A Claisen-Schmidt condensation was deployed to construct the chalcone scaffold followed by removal of MOM protecting groups under acidic conditions that were optimized to prevent concomitant cyclization to the flavone.