title: Total synthesis and evaluation of C26-hydroxyepothilone D derivatives for photoaffinity labeling of beta-tubulin.
abstract: Three photoaffinity labeled derivatives of epothilone D were prepared by total synthesis, using efficient novel asymmetric synthesis methods for the preparation of two important synthetic building blocks. The key step for the asymmetric synthesis of (S,E)-3-(tert-butyldimethylsilyloxy)-4-methyl-5-(2-methylthiazol-4-yl)pent-4-enal involved a ketone reduction with (R)-Me-CBS-oxazaborolidine. For the synthesis of (5S)-5,7-di[(tert-butyldimethylsilyl)oxy]-4,4-dimethylheptan-3-one an asymmetric Noyori reduction of a beta-ketoester was employed. The C26 hydroxyepothilone D derivative was constructed following a well-established total synthesis strategy and the photoaffinity labels were attached to the C26 hydroxyl group. The photoaffinity analogues were tested in a tubulin assembly assay and for cytotoxicity against MCF-7 and HCT-116 cancer cell lines. The 3- and 4-azidobenzoic acid analogues were found to be as active as epothilone B in a tubulin assembly assay, but demonstrated significantly reduced cellular cytotoxicity compared to epothilone B. The benzophenone analogue was inactive in both assays. Docking and scoring studies were conducted that suggested that the azide analogues can bind to the epothilone binding site, but that the benzophenone analogue undergoes a sterically driven ligand rearrangement that interrupts all hydrogen bonding and therefore protein binding. Photoaffinity labeling studies with the 3-azidobenzoic acid derivative did not identify any covalently labeled peptide fragments, suggesting that the phenylazido side chain was predominantly solvent-exposed in the bound conformation.
authors: Department of Medicinal Chemistry, University of Kansas, 1251 Wescoe Hall Drive, Lawrence, Kansas 66045, USA.
authors: Emily A
authors: EA
authors: Reiff
authors: Sajiv K
authors: SK
authors: Nair
authors: John T
authors: JT
authors: Henri
authors: Jack F
authors: JF
authors: Greiner
authors: Bollu S
authors: BS
authors: Reddy
authors: Ramappa
authors: R
authors: Chakrasali
authors: Sunil A
authors: SA
authors: David
authors: Ting-Lan
authors: TL
authors: Chiu
authors: Elizabeth A
authors: EA
authors: Amin
authors: Richard H
authors: RH
authors: Himes
authors: David G
authors: DG
authors: Vander Velde
authors: Gunda I
authors: GI
authors: Georg
mesh_terms: D034261:Epothilones / Q000138:chemical synthesis* / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D015335:Molecular Probes / Q000138:chemical synthesis*; D015394:Molecular Structure; D019920:Photoaffinity Labels / Q000138:chemical synthesis* / Q000737:chemistry; D014404:Tubulin / Q000737:chemistry*; D050257:Tubulin Modulators / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: C547702:C26-hydroxyepothilone D; D034261:Epothilones; D015335:Molecular Probes; D019920:Photoaffinity Labels; D014404:Tubulin; D050257:Tubulin Modulators