Research Article
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Future
Medicinal Chemistry
Design and synthesis of novel pegylated iron chelators with decreased metabolic rate
Background: Deferiprone has proved to be a successful iron selective chelator in a range of pathologies. However, its use is limited by rapid phase II metabolism, necessitating the administration of large doses. In an attempt to modify metabolic rate of this class of compounds, a range of pegylated 3-hydroxypyridin-4-ones has been synthesized. Experimental: The synthetic route in which the polyethylene glycol counterparts are introduced to a protected pyran ring involves either a Williamson etherification reaction or direct addition leading to polyethylene glycol-containing precursors. Results & discussion: The introduction of the pegylated substituent was found to lead to a relatively low rate of metabolism for some of the derivatives (6a, 6b, 8a and 8b), offering a possible improvement over deferiprone.
The most frequent treatment of inherited hematological diseases such as β-thalassemia major is to maintain high levels of hemoglobin by regular blood transfusion [1] . Repeated transfusion leads to elevated body iron levels due to the inability of humans to excrete iron via the kidney. Excess iron is mainly located within the liver and other highly perfused organs leading to tissue damage, organ failure and eventually death [2] . Complications associated with elevated iron levels can be largely avoided by the use of iron-specific chelating agents [3] . 3-hydroxypyridin-4-ones (HPOs) are currently one of the main candidates for the development of orally active iron chelators [4] . Indeed, the 1,2-dimethyl derivative (deferiprone) has shown considerable promise in the clinic [5,6] . Unfortunately, deferiprone is rapidly metabolized in the liver [7] and thus the dose of deferiprone required to maintain a thalassaemia patient in negative iron balance is relatively high, typically in the region of 75–100 mg·kg-1day-1 [8] . In an attempt to moderate the physicochemical properties of deferiprone, such that the molecules experience a slower rate of metabolism, we decided to incorporate PEG functions into the hydroxypyridinone structure. Pegylation of therapeutic proteins/
10.4155/fmc.15.154 © 2015 Future Science Ltd
drugs has significantly improved the treatment of several chronic diseases, including hepatitis C, leukemia, rheumatoid arthritis and Crohn’s disease, such as in the case of pegademase [9] or certolizumab pegol [10] , which are established pegylated pharmaceuticals. The advantage of polyethylene glycol resides in the fact that it possesses, in addition to its favorable biological properties, good solubility in both aqueous and organic milieu, good flexibility and high hydration that increases its hydrodynamic volume [11] . Pegylation of desferrithiocin analogs has been used successfully to produce highly efficient iron scavenging molecules [12] . One such chelator, deferitazole [13] , has recently been successful in Phase II clinical trials [14] . In the present study, we have synthesized a series of 1-, 2-, 6- substituted and 2, 6- disubstituted pegylated hydroxypyridinones. The physicochemical properties of this series of compounds have been characterized, together with their susceptibility towards metabolism.
Junpei Li‡,1, Zidong Lu‡,2, Xiaole Kong2, Yongmin Ma3, Xingyuan Zhang1, Sukhvinder S Bansal2, Vincenzo Abbate*,2 & Robert C Hider2 1 Department of Polymer Science & Engineering, University of Science & Technology of China, Hefei, Anhui 230026, China 2 Institute of Pharmaceutical Science, King’s College London, SE1 9NH London, UK 3 College of Pharmaceutical Sciences, Zhejiang Chinese Medical University, 310053 Hangzhou, China *Author for correspondence: Tel.: +44 (0)20 7848 4501 Fax: +44 (0)20 7848 4800
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Experimental General
Reagents were reagent grade quality from Sigma-Aldrich and were used with-
Future Med. Chem. (2015) 7(18), 2439–2449
part of
ISSN 1756-8919
2439
Research Article Li, Lu, Kong et al.
Key terms 3-hydroxypyridin-4-ones: Small hydrophilic molecules which act as a bidentate ligands. Pegylated hydroxypyridinones: Hydroxypyridinones with enhanced water solubility.
out further purification. Column chromatography separations were performed on Merck silica gel 60 (0.04−0.063 mm). 1H NMR and 13C NMR spectra were recorded using a Bruker Avance 400 (400 MHz) NMR spectrometer. Chemical shifts (δ) are reported in ppm downfield from the internal standard tetramethylsilane. J values are in hertz (Hz), and splitting patterns are designated as follows: s (singlet), bs (broad singlet), d (doublet), t (triplet) and m (multiplet). The Electrospray Ionisation-MS analyses were performed using a Waters/Micromass (Manchester, UK) ZQ-2000 mass spectrometer. High resolution MS (HRMS) was carried out by the Mass Spectrometry Facility, School of Biomedical Science, King’s College London. Purity (≥95%) was established by HPLC analyses. Details of the synthetic procedures are provided in the Supplementary Information. Determination of pKa values & iron stability constants
The automatic titration system used in this study comprised of an autoburette (Metrohm Dosimat 765 liter ml syringe) and Mettler Toledo MP230 pH meter with Metrohm pH electrode (6.0133.100) and a reference electrode (6.0733.100). 0.1 M KCl electrolyte solution was used to maintain the ionic strength. The temperature of the test solutions was maintained in a thermostatic jacketed titration vessel at 25°C ± 0.1°C by using a Techne TE-8J temperature controller. The solution under investigation was stirred vigorously during the experiment. A Gilson Mini-plus#3 pump with speed capability (20 ml/min) was used to circulate the test solution through a Hellem quartz flow cuvette. For the stability constant determinations, a 50 mm path length cuvette was used, and for pKa determinations, a cuvette path length of 10 mm was used. The flow cuvette was mounted on an HP 8453 UV-visible spectrophotometer. All instruments were interfaced to a computer and controlled by a Visual Basic program. Automatic titration and spectral scans adopted the following strategy: the pH of a solution was increased by 0.1 pH unit by the addition of KOH from the autoburette; when pH of readings varied by
