High-content screening and mechanism-based evaluation of estrogenic botanical extracts

Symptoms associated with menopause can greatly affect the quality of life for women. Botanical dietary supplements have been viewed by the public as safe and effective despite a lack of evidence indicating a urgent necessity to standardize these supplements chemically and biologically. Seventeen plants were evaluated for estrogenic biological activity using standard assays: competitive estrogen receptor (ER) binding assay for both alpha and beta subtypes, transient transfection of the estrogen response element luciferase plasmid into MCF-7 cells expressing either ER alpha or ER beta, and the Ishikawa alkaline phosphatase induction assay for both estrogenic and antiestrogenic activities. Based on the combination of data pooled from these assays, the following was determined: a) a high rate of false positive activity for the competitive binding assays, b) some extracts had estrogenic activity despite a lack of ability to bind the ER, c) one extract exhibited selective estrogen receptor modulator (SERM) activity, and d) several extracts show additive/synergistic activity. Taken together, these data indicate a need to reprioritize the order in which the bioassays are performed for maximal efficiency of programs involving bioassay-guided fractionation. In addition, possible explanations for the conflicts in the literature over the estrogenicity of Cimicifuga racemosa (black cohosh) are suggested.     

Enhanced epimerization of glycosylated amino acids during solid-phase peptide synthesis

Glycopeptides are extremely useful for basic research and clinical applications, but access to structurally defined glycopeptides is limited by the difficulties in synthesizing this class of compounds. In this study, we demonstrate that many common peptide coupling conditions used to prepare O-linked glycopeptides result in substantial amounts of epimerization at the α position. In fact, epimerization resulted in up to 80% of the non-natural epimer, indicating that it can be the major product in some reactions. Through a series of mechanistic studies, we demonstrate that the enhanced epimerization relative to nonglycosylated amino acids is due to a combination of factors, including a faster rate of epimerization, an energetic preference for the unnatural epimer over the natural epimer, and a slower overall rate of peptide coupling. In addition, we demonstrate that use of 2,4,6-trimethylpyridine (TMP) as the base in peptide couplings produces glycopeptides with high efficiency and low epimerization. The information and improved reaction conditions will facilitate the preparation of glycopeptides as therapeutic compounds and vaccine antigens.