Natural Product Synthesis DOI: 10.1002/ange.200704577 Asymmetric Synthesis and Biological Properties of Uncialamycin and 26-epi-Uncialamycin** K. C. Nicolaou,* Jason S. Chen, Hongjun Zhang, and Ana Montero Dedicated to Professor Ryoji Noyori on the occasion of his 70th birthday Among the most potent antitumor antibiotics are the enediynes, [1] one of which, calicheamicin g 1 I (Mylotarg, Gemtuzumabozogamicin),iscurrentlyinuseasananticancer agent. [2] Uncialamycin (1, Figure1) is a newly discovered enediyne [3] isolatedfromanunspecifiedstrainofStreptomy- cete related to Streptomyces cyanogenus . In preliminary investigations,uncialamycinrevealedstrikingactivityagainst Escherichia coli [minimum inhibitory concentration (MIC) = 0.002 mgmL 1 ], Staphylococcus aureus (MIC = 0.0000064 mgmL 1 ), and Burkholderia cepacia (MIC = 0.001 mgmL 1 ),thelatterbeingresponsibleforlunginfections incysticfibrosispatients. [4] Thesephenomenalresultselevate uncialamycin to a promising lead for drug discovery in the areasofcancerandinfectiousdiseases.However,theextreme scarcityofthissubstance(only300 mgwasisolated)hampered furtherbiologicalstudies.Hereinwedescribetheasymmetric synthesis of uncialamycin and its bioactive isomer, 26-epi- uncialamycin (2 ), and detailed studies into their in vitro DNA-cleaving, antibacterial, and cytotoxic properties. We foundthat 1 and 2 promotesingle-anddouble-strandcutsin plasmid DNA and exhibit powerful antibacterial properties against several strains, including methicillin-resistant Staph- ylococcus aureus (MRSA; MIC = 0.0002 mgmL 1 for 1) and vancomycin-resistant Enterococcus faecalis (VRE; MIC = 0.002 mgmL 1 for 1) as well as potent activities against a broadpanelofcancercells,includingTaxol-resistantovarian cells (1A9/PTX10; IC 50 = 610 11 m for 1) and epothiloneB resistant cells (1A9/A8; IC 50 = 910 12 m for 1). Our results demonstratetheviabilityofchemicalsynthesisasasourceof thesevaluablecompoundsandrenderthemreadilyavailable for biological studies. Furthermore, our investigations dem- onstratethepotentialofthesecompoundsasdrugcandidates for the treatment of cancer and infectious diseases and confirm their DNA-cleaving mechanism of action. Given thesefindings,wesuggestthatantibodyconjugates [5] ofthese toxinsmayleadtotargetingagentsofclinicalimportance. Owingtothelownaturalabundanceofuncialamycin(1), the original investigation of its structure [3] stopped short of assigning its stereochemistry at C26 and offered only a speculationastothemolecule)sabsoluteconfiguration.While our recent synthesis of racemic uncialamycin (1)and26-epi- uncialamycin (2) provided an answer to the question of the relativestereochemistryatC26,itneithersolvedtheissueof supply of the naturally occurring enantiomer of the natural product nor determined its absolute configuration. [6] To resolve these issues and facilitate further biological inves- tigations, we resorted to a catalytic asymmetric synthesis of uncialamycin(1),highlightsofwhichareshowninScheme1. Thus,thereadilyavailableprochiralquinolinecarboxylicacid 3 [6] was converted to its methyl ester 4 through the initial action of thionyl chloride followed by treatment of the resultingacidchloridewithmethanolinthepresenceofEt 3 N and DMAP in 65% overall yield. Noyori reduction [7] of the methyl ketone moiety within 4 (ruthenium catalyst 5, HCO 2 H, Et 3 N) resulted in the formation of g-lactone 7, presumably via intermediate hydroxy ester 6,in95%yield and93% ee.Whilethisoutcomewassatisfactory,difficulties in maintaining the configurational integrity of the generated asymmetric center in 7 during its obligatory conversion to intermediate 8 under acidic conditions led us to explore an alternative approach to reach compound 8 from starting material 3. Figure 1. Structures of uncialamycin (1) and 26-epi-uncialamycin (2). [*] Prof. Dr. K. C. Nicolaou, J. S. Chen, Dr. H. Zhang, Dr. A. Montero Department of Chemistry and The Skaggs Institute for Chemical Biology The Scripps Research Institute 10550 North Torrey Pines Road, La Jolla, CA 92037 (USA) Fax: (+ 1)858-784-2469 E-mail: kcn@scripps.edu and Department of Chemistry and Biochemistry University of California, San Diego 9500 Gilman Drive, La Jolla, CA 92093 (USA) [**] We thank the National Cancer Institute (NCI) screening program (http://dtp.nci.nih.gov/) for testing our compounds in the 60-cell- line panel and Dr. R. N. Misra for his assistance. We thank Dr. P. Giannakakou for providing the 1A9, 1A9/PTX10, 1A9/PTX22, and 1A9/A8 cell lines. We also acknowledge Drs. D. H. Huang, G. Siuzdak, R. K. Chadha, R. Ghadiri, and I. Hwang for assistance with NMR spectroscopy, mass spectrometry, X-ray crystallography, bacterial assays, and cytotoxicity assays, respectively. This work was supported by The Skaggs Institute for Chemical Biology, a National Defense Science and Engineering Graduate fellowship (to J.S.C.), and a MEC/Fulbright fellowship (to A.M.). Supporting information for this article is available on the WWW under http://www.angewandte.org or from the author. Angewandte Chemie 191 Angew. Chem. 2008, 120, 191 –195 # 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim