Intellectual curiosity has always been one of the major driving forces leading to new advances in chemistry. At the onset of the 20th century, the fact that biaryls could be optically active even if lacking asymmetrically substituted carbon atoms arose interest, hinting at a novel type of stereomerism. It took quite a while (and some bizarre explanations)1 until in 1922 Christie and Kenner2 first correctly recognized that the phenomenon was the consequence of a hindered rotation about the aryl-aryl single bondshence termed atropisomerism by Kuhn. Still, no particular attention was initially paid to this class of stereoisomers until enantiomerically pure biaryls, such as BINAP (1),3 were found to be excellent ligands in asymmetric catalysis and until the chiral biaryl unit was recognized as the decisive structural element of many natural products (Figure 1).4,5 With the modern screening techniques and the bioassayguided search for novel compounds, the number of isolated axially chiral natural biaryls is steadily increasing.4 This class of secondary metabolites is characterized by a broad structural diversity, reaching from relatively simple molecules like the C2-symmetric biphenyl 2, which solely contains the element of axial chirality,6 to more complex compounds, like, e.g., the dimeric naphthylisoquinoline alkaloids michellamine A [(P,P)-3] and its axial epimer (i.e., its atropodiastereomer), michellamine B [(P,M)-3],7,8 which possess even three biaryl axes, of which the two outer ones are stereogenic, while * To whom correspondence should be addressed. E-mail: bringmann@ chemie.uni-wuerzburg.de; breuning@chemie.uni-wuerzburg.de. † These authors contributed equally to this work. ‡ Present address: Institute of Organic Chemistry, RWTH Aachen, Landoltweg 1, 52074 Aachen, Germany. § Present address: Kekulé Institute of Chemistry and Biochemistry, University of Bonn, Gerhard-Domagk Str. 1, 53121 Bonn, Germany. Gerhard Bringmann was born in 1951 and studied chemistry in Gie en and Münster, Germany. After his Ph.D. with Prof. B. Franck in 1978 and postdoctoral studies with Prof. Sir D. H. R. Barton in Gif-sur-Yvette (France), he passed his habilitation at the University of Münster in 1984. In 1986, he received offers for full professorships of Organic Chemistry at the Universities of Vienna and Würzburg, of which he accepted the latter in 1987. In 1998, he was offered the position of director at the Leibniz Institute of Plant Biochemistry in Halle, which he declined. His research interests focus on the field of analytical, synthetic, and computational natural product chemistry, i.e., on axially chiral biaryls. He received several prizes and awards, among them the Otto-Klung Award in chemistry (1988), the Prize for Good Teaching of the Free State of Bavaria (1999), the Adolf-Windaus Medal (2006), the Honorary Doctorate of the University of Kinshasa (2006), the Paul-J.-Scheuer Award (2007), and the Honorary Guest Professorship of Peking University (2008). Chem. Rev. 2011, 111, 563–639 563

Atroposelective total synthesis of axially chiral biaryl natural products.

The year 2017 marks the twentieth anniversary of terpenoid cyclase structural biology: a trio of terpenoid cyclase structures reported together in 1997 were the first to set the foundation for understanding the enzymes largely responsible for the exquisite chemodiversity of more than 80000 terpenoid natural products. Terpenoid cyclases catalyze the most complex chemical reactions in biology, in that more than half of the substrate carbon atoms undergo changes in bonding and hybridization during a single enzyme-catalyzed cyclization reaction. The past two decades have witnessed structural, functional, and computational studies illuminating the modes of substrate activation that initiate the cyclization cascade, the management and manipulation of high-energy carbocation intermediates that propagate the cyclization cascade, and the chemical strategies that terminate the cyclization cascade. The role of the terpenoid cyclase as a template for catalysis is paramount to its function, and protein engineering can...

Structural and Chemical Biology of Terpenoid Cyclases.

Gossypol has demonstrated in vitro effects on cell cycle regulation and anti-tumor activity against mammary carcinoma cell lines. This Phase I/II study assesses both the effect of gossypol on cell cycle regulatory proteins in vivo and the clinical effect. Twenty women with refractory metastatic breast cancer received oral gossypol at daily doses between 30 and 50mg per day. Gossypol plasma levels were measured (n=8) and the modulation of the retinoblastoma (Rb) gene protein and Cyclin D1 was assessed by serial biopsies (n=4). Grade I–II toxicities with gossypol treatment included nausea in 30% of patients, fatigue 15%, emesis 15%, altered taste sensation 15% and diarrhea in 10% of patients. Two of the three patients receiving 50mg/day experienced dose limiting dermatologic toxicity (grade III). One patient had a minor response and two patients had stable disease with >50 decline in serial assessments of the serum tumor markers. Immunohistochemical analysis of cyclin D1 and Rb expression in serial biopsies of four patients revealed both a concurrent decrease in cyclin D1 expression and an increase in nuclear Rb expression in three patients. The maximal tolerated dose (MTD) of gossypol was 40mg/day. Gossypol appears to affect the expression of Rb protein and cyclin D1 in breast cancer metastases at doses achievable, yet had negligible antitumor activity against anthracycline and taxane refractory metastatic breast cancer. The cell cycle regulatory effects of gossypol suggest a potential role for gossypol as a modulating agent in conjunction with other cell cycle specific compounds.

Oral Gossypol in the Treatment of Patients with Refractory Metastatic Breast Cancer: A Phase I/II Clinical Trial

Molecular mechanism of gossypol-induced cell growth inhibition and cell death of HT-29 human colon carcinoma cells.

Gossypol has received significant attention as a result of its potential therapeutic application as a male antifertility agent. Furthermore, recent research examining the biological activity of gossypol has revealed a number of other promising lines of enquiry. These have focused on the antitumour, antiviral and antioxidant actions of the compound in various disease states. This article provides an overview of the studies on the biological activity of gossypol, with particular attention paid to the mechanisms of its activity and its prospect as a medicinal product.

Investigations on gossypol: past and present developments.

https://www.gynecologiconcology-online.net/article/0090-8258(89)90623-9/pdf

Ann E. Rhinehardt

Papers

Antiproliferative effect of gossypol and its optical isomers on human reproductive cancer cell lines.