approach could be used for other ketone containing drugs with
low oral activity, such as the antibiotic pleuromutilin and certain
cathepsin K inhibitors under development by GSK.22 Addition-
ally, as prodrugs continue to play an ever increasing role in drug
development and optimisation, expanding the range of functional-
ity that can be converted into prodrugs will increase the number of
tools available to medicinal chemists for drug development. Fur-
thermore, active targeting of these prodrugs to membrane trans-
porters such as PepT1 may overcome a variety of problems such
as oral bioavailability, specific tissue distribution and excretion.
The authors wish to acknowledge the University of Oxford,
where most of the biological testing described was carried out by
DM and MP. The Wellcome Trust is thanked for generous financial
support.
Fig. 3 A: Relative rate of mediated apical to basolateral transport of 16
and 17 in Caco-2 monolayers, normalised to the transport rate of FSA
in the same culture of cells. B: Percentage of the 2 mM apical load of 16
and 17 that was transported across the Caco-2 monolayer in 1 hour by a
mediated transport route (normalised to a mean value for 2 mM FSA of
1.22 0.30%, n = 3 cultures).
Notes and references
1 C. A. Lipinski, F. Lombardo, B. W. Dominy and P. J. Feeney, Adv. Drug
Delivery Rev., 2001, 46, 3–26.
2 E. M. Wright, B. A. Hirayama, D. D. F. Loo, E. Turk, K. Hager,
in Physiology of the Gastrointestinal Tract, Raven Press, New York,
3rd edn., 1994, vol. 2, pp. 1751–1772. V. Ganapathy, M. Brandsch,
F. H. Leibach, in Physiology of the Gastrointestinal Tract, Raven Press,
New York, 3rd edn., 1994, vol. 2, pp. 1773–1794.
faster than 17. This is consistent with it having lower affinity for
PepT1 and implies that the release of the substrate to give an empty
transporter for re-orientation is part of the rate-limiting step in the
catalytic transport cycle of PepT1.21
The pH dependence of this transport was shown by examining
the PepT1 mediated rate of transport after one hour (as per
method above) at pH 5.5 and 7.4 (Fig. 4). If the compounds are
substrates of the proton-coupled PepT1 transporter, as previous
results suggested, the transport rates should be faster at pH 5.5
than at pH 7.4.5 In each case, a significantly slower transport rate
was observed at pH 7.4, approximately 50% that of the pH 5.5 rate.
This pH dependence data is fully consistent with the previous data
in demonstrating that the compounds are substrates of PepT1.
3 B. Testa, Biochem. Pharmacol., 2004, 68, 2097–2106.
4 H. Kumpulainen, N. Mahonen, M. L. Laitinen, M. Jaurakkajarvi,
H. Raunio, R. O. Juvonen, J. Vepsalainen, T. Jarvinen and J. Rautio,
J. Med. Chem., 2006, 49, 1207–1211.
5 M. Brandsch, I. Ku¨tter and E. Bosse-Doenecke, J. Pharm. Pharmacol.,
2008, 60, 543–585; T. Terada and K. Inui, Curr. Drug Metab., 2004, 5,
1–10; H. Daniel, Annu. Rev. Physiol., 2004, 66, 361–384.
6 P. D. Bailey, (The University of Manchester, UK). European Patent
Office, Int. Application No.: WO2005067978, 2005.
7 M. A. Brown, D. W. Gammon and J. E. Casida, J. Agric. Food Chem.,
1983, 31, 1091–1096; for example, total hydrolysis of an oxime ether in
this paper took place in <1 h at 55 ◦C in 1M-HCl.
8 M. A. Tirmenstein, Toxicology in Vitro, 1993, 7, 645–652; D. E.
Richards, K. B. Begley, D. G. DeBord, K. L. Cheever, W. W. Weigel,
M. A. Tirmenstein and R. E. Savage, Arch. Toxicol., 1993, 67, 531–537.
9 A. Bouzide and G. Sauve´, Tetrahedron Lett., 1997, 38, 5945–5948.
10 S. B. Mirviss, J. Org. Chem., 1989, 54, 1948–1951.
11 W. M. Pearlman, Tetrahedron Lett., 1967, 8, 1663–1664.
12 B. S. Pedersen, S. Scheibye, N. H. Nilsson and S. O. Lawesson, Bull.
Soc. Chim. Belg., 1978, 87, 223–228; M. P. Cava and M. I. Levinson,
Tetrahedron, 1985, 41, 5061–5087.
13 C. S. Temple, J. R. Bronk, P. D. Bailey and C. A. R. Boyd, Pflu¨gers
Arch. – Eur. J. Physiol., 1995, 430, 825–829.
14 D. Meredith, C. A. R. Boyd, J. R. Bronk, P. D. Bailey, K. M. Morgan,
I. D. Collier and C. S. Temple, J. Physiol. (London), 1998, 512, 629–634.
15 B. S. Vig, T. R. Stouch, J. K. Timoszyk, Y. Quan, D. A. Wall, R. L.
Smith and T. N. Faria, J. Med. Chem., 2006, 49, 3636–3644.
16 D. Meredith, C. S. Temple, N. Guha, C. J. Sword and C. A. R. Boyd,
Eur. J. Biochem., 2000, 267, 3723–3728.
17 C. S. Temple, A. K. Stewart, D. Meredith, N. A. Lister, K. M. Morgan,
I. D. Collier, R. D. Vaughan-Jones, C. A. R. Boyd, P. D. Bailey and
J. R. Bronk, J. Biol. Chem., 1998, 273, 20–22.
18 I. J. Hidalgo, T. J. Raub and R. T. Borchardt, Gastroenterology, 1989,
96, 736–749.
19 P. V. Balimane, S. Chong, K. Patel, Y. Quan, J. Timoszyk, Y.-H. Han,
B. Wang, B. Vig and T. N. Faria, Arch. Pharm. Res., 2007, 30, 507–518.
20 R. K. Bhardwaj, D. Herrera-Ruiz, P. J. Sinko, O. S. Gudmundsson and
G. Knipp, J. Pharmacol. Exper. Ther., 2005, 314, 1093–1100.
21 C. S. Temple, P. D. Bailey, J. R. Bronk and C. A. R. Boyd, J. Physiol.,
1996, 494, 795–808.
Fig. 4 pH dependence of apical to basolateral PepT1 transport rates
across Caco-2 monolayers after one hour of FSA (standard), 16 and 17
(normalised to the mean rate of transport for each compound at pH 5.5,
n = 3 cultures). ** p < 0.01, * p < 0.05.
22 G. Brooks, W. Burgess, D. Colthurst, J. D. Hinks, E. Hunt, M. J.
Pearson, B. Shea, A. K. Takle, J. M. Wilson and G. Woodnutt, Bioorg.
Med. Chem. Lett., 2001, 9, 1221–1231; E. Hunt, Drugs Fut., 2000, 25,
1163–1168; D. G. Barrett, J. G. Catalano, D. N. Deaton, S. T. Long,
R. B. McFadyen, A. B. Miller, R. M. Larry, V. Samano, F. X. Tavares,
K.-J. Wells-Knecht, L. L. Wright and H.-Q. Q. Zhou, Bioorg. Med.
Chem., 2007, 17, 22–27.
In conclusion, the synthesis, in vitro binding and transport
of hydroxyimine prodrugs of the anti-inflammatory ketone drug
nabumetone via PepT1 has been shown. This is the first example
of targeting a ketone prodrug towards PepT1 absorption. Whilst
the model ketone drug studied is itself orally active, we feel this
This journal is
The Royal Society of Chemistry 2009
Org. Biomol. Chem., 2009, 7, 1064–1067 | 1067
©