Synthesis of Natural and Unnatural Products
1) Total Synthesis of Citrofulvicin
We are currently engaged in efforts towards a total synthesis of the natural product citrofulvicin, a polyketide derived from the fungus Penicillium velutinum. Citrofulvicin was isolated in 2018 and is reported to have anti-osteoporotic activity. We have recently published preliminary work towards this total synthesis, consisting of a nine-step synthetic route to a model system of citrofulvicin consisting of defunctionalized aromatic systems. (K. Doytchinova, J. Winkler, “Synthesis of the Core Ring System of the Antiosteoporotic Citrofulvicin,” Org. Lett. 2021, 23, 4575-4578). This synthetic route takes advantage of the pseudo-dimeric nature of the natural product.
2) Design and Synthesis of Spatially Adressable Helical Structures
For some time we have been engaged in the synthesis of foldamers and helical mimetics (J. Winkler, E. Piatnitski, J. Mehlmann, J. Kasparec, P. Axelsen, “Design and Synthesis of Novel Foldamers Based on an Anthracene Diels-Alder Adduct,” Angew. Chem. Int. Ed. Engl. 2001, 40, 743-745). (Design and Synthesis of Novel Foldamers Based on an Anthracene Diels-Alder Adduct) The design and synthesis of spatially addressable helical systems, as shown schematically in 1 (Figure 1) is important for the design of small molecules that could be used to disrupt protein-protein interactions (PPIs), which until recently had been characterized as “undruggable.” We have recently demonstrated that double Buchwald-Hartwig coupling of a-bromoanilines leads to the synthesis of phenazines (J. Winkler, B. Twenter, T. Gendrineau, “Synthesis of Substituted Phenazines via Palladium-Catalyzed Aryl Ligation,” Heterocycles, 2012, 84, 1345-1353) (Synthesis of Substituted Phenazines via Palladium-Catalyzed Aryl Ligation) and, in unpublished work from our laboratory, we have applied this methodology to the synthesis of helical molecules such as 2 (Figure 1) from suitably functionalized Troger’s base monomers. Current work in our laboratory is focused on the development of spatially addressable systems using this approach and use of the derived structures as inhibitors of PPIs, as well as the de novo design of Troger-like structures that will facilitate the functionalization of these oligomeric systems.
3) Design and Synthesis of Hedgehog Signaling Inhibitors
The unique structure of the steroidal alkaloid cyclopamine along with its important biological function as an inhibitor of the signaling protein Smoothened (SMO) makes its synthesis and study important goals. We have designed a series of analogs of cyclopamine based on structure of estrone that have led to the estrone analog and the oxetane (J. Winkler, A. Isaacs, C. Xiang, V. Baubet, N. Dahmane, “Design, Synthesis and Biological Evaluation of Estrone-Derived Hedgehog Signaling Inhibitors,” Tetrahedron 2011, 67, 10261-10266 and references cited therein; Figure 2). The oxetane (53 nM) is more potent in cellular assays than either cyclopamine (104 nM) or the estrone analog (204 nM). Further studies on the role of the stereochemistry of the oxetane on the observed potency as well as the development of more potent analogs based on the modeling shown in Figure 2 is currently underway in our laboratory.
4) Synthesis and Study of Neokauluamine, A Dimeric Manzamine Alkaloid with Potent Activity against Infectious Disease and Cancer
Our long-standing interest in the manzamine alkaloids led us to the highly complex structure of neokauluamine (Figure 3). We are exploring a biomimetic approach to the total synthesis of 3 and also exploring the hypothesis that the biological activity of 3 is due to the orientation of the two beta-carboline heterocycles on this complex scaffold. We have recently published preliminary studies on the development of such simple model systems (J. Chatwichien, S. Basu, M. Murphy, M. Hamann, J. Winkler, “Design, Synthesis and Biological Evaluation of beta-Carboline Dimers Based on the Structure of Neokauluamine,” Tet. Lett. 2015, 56, 3515-3517) and working toward the development of other mimetics for the neokauluamine structure.
Collaborative Projects at the Interface of Chemistry and Biology
1) Design and Synthesis of Autophagy Inhibitors Based on the Structure of the Antimalarial Drug Chloroquine | (Amaravadi Laboratory, University of Pennsylvania School of Medicine)
The development of autophagy (autophagocytosis) inhibitors represents an important approach to the potentiation of the effects of cancer chemotherapeutic agents. We have recently developed bis-aminoquinolines as autophagy inhibitors and have reported that these compounds demonstrate single-agent antitumor efficacy in vitro and in vivo (Q. McAfee, Z. Zhang, A. Samanta, S. Levi, X. Ma, S. Piao, J. Lynch, T. Uehara, A. Sepulveda, L. Davis, J. Winkler, R. Amaravadi, “A Novel Autophagy Inhibitor with Single Agent Antitumor Activity Reproduces the Phenotype of a Genetic Autophagy Deficiency,” Proc. Natl. Acad. Sci. 2012, 109, 8253-8258). Current efforts in our laboratory are directed toward elucidating the mechanism of action of these compounds as well as developing more potent and selective ligands that could lead to new drugs for cancer chemotherapy.
2) Development of Small Molecule Ligands for Hemoglobin (Hb) | (Zapol Laboratory, Massachusetts General Hospital and Harvard Medical School)
We are working with the Zapol Laboratory at Harvard to develop small molecule ligands that can be used to 1) reduce sickling of sickle cell red blood cells; 2) to inhibit carbon monoxide (CO) binding and/or enhance CO release from CO-Hb; and 3) to inhibito the scavenging of Hb by nitric oxide (NO). Starting from screening hits and X-ray structural data of ligand-Hb interactions (an example of which is shown below for the ligand IRL-2500), we are optimizing both potency and biophysical properties to develop small molecules that can be used in clinical trials.
3) Development of Isozyme Selective AKR1C3 Inhibitors for the Treatment of Prostate Cancer | (Penning Laboratory, University of Pennsylvania School of Medicine)
For some time we have been involved in the development of isozyme-selective aldo-keto-reductase (AKR) inhibitors for the manipulation of steroid biosynthesis in castrate-resistant prostate cancer. Because there are several isozymes of the target protein, the development fo isozyme-selective inhibitors is an important goal. Recent work from our laboratories has established the viability of this strategy (A. Adeniji, B. Twenter, M. Byrns, Y. Jin, J. Winkler, T. Penning, “Discovery of Substituted 3-(Phenylamino)benzoic acids as Potent and Selective Inhibitors of Type 5 17β-Hydroxysteroid Dehydrogenase (AKR1C3),” Bioorg. Med. Chem. Lett, 2011, 21, 1464-1468; M. Chen, A. Adeniji, B. Twenter, J. Winkler, D. Christianson, T. Penning, “Crystal Structures of AKR1C3 Containing an N-(Aryl)amino-benzoate Inhibitor and a Bifunctional AKR1C3 Inhibitor and Androgen Receptor Antagonist. Therapeutic Leads for Castrate Resistant Prostate Cancer,” Bioorg. Med. Chem. Lett. 2012, 22, 3492-3497; A. Adeniji, B. Twenter, M. Byrns, U. Jin, M. Chen, J. Winkler, T. Penning, “Development of Potent and Selective Inhibitors of Aldo-Keto Reductase 1C3 (type 5 17-hydroxysteroid dehydrogenase) Based on N-Phenyl-Aminobenzoates and Their Structure Activity Relationships,” J. Med. Chem. 2012, 55, 2311-2323) and work is currently underway to develop more potent structures.
4) Design, Synthesis and Biological Evaluation of BRAF Kinase Inhibitors as Cancer Chemotherapies | (Marmorstein Laboratory, University of Pennsylvania School of Medicine)
The BRAF oncoprotein is mutated in about half of malignant melanomas and other cancers. We have identified a family of quinolol/naphthol compounds that selectively inhibit the BRAF mutant (V600E; structures of PLX 4720 and quinolol ligand 1 in the BRAF binding site (J. Qin, P. Xie, C. Ventochilla, G. Zhou, A. Vultur, Q. Chen, Q. Liu, M. Herlyn, J. Winkler, R. Marmorstein, “Identification of a Novel Family of BRAF(V600E) Inhibitors,” J. Med. Chem. 2012, 55, 5220-5230). Current work in our laboratory is directed toward optimizing the properties of these structures.