M. B. Tollefson et al. / Bioorg. Med. Chem. Lett. 13 (2003) 3727–3730
3729
Table 1. In vitro assay of 1,2-benzothiazepines 1,1-dioxides that
inhibit ASBT-mediated uptake of [14C]-taurocholate in H14 cells
the orientation of the inhibitor. This altered alignment
prevents the beneficial binding of the 40-OH group as
seen in the secondary sulfonamides.
Efforts to prepare a more water soluble 1,2-benzothi-
azepine resulted in the synthesis of more potent ASBT
inhibitors. Several side chains linking a quaternary
ammonium salt to the 5-phenyl ring were investigated.
An amide linker was constructed from the 3-amino
compounds (15c and 16b) and then reacted with trie-
thylamine to afford 15g, 16h and 16i. The quaternary
ammonium salts (15g, 16h and 16i) exhibited potencies
3–14 times greater than their alkyl halide precursors
(15f, 16f and 16g) indicating the importance of the
ammonium group for optimal activity. It is also impor-
tant to note that the potencies of 15g, 16 h and 16i are
substantially better than the simple 30-NO2 and 30-NH2
precursors (15b, 15c, 16a, and 16b), and that 15g is one
of the most potent compounds to date (IC50=1.6 nM).
We believe that the quaternary ammonium salt may be
exposed to solvent and its main function to be increased
solubility.
Compd
R
R0
IC50 (nM)
2
—
CH2Ph
CH2Ph
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
H
H
H
H
H
H
H
H
—
3-NO2
3-NHEt
3-NO2
3-NH2
3-OMe
4-OMe
4-OH
48
>1000
2500
1200
320
1200
570
580
970
690
320
83
17a
17b
16a
16b
16c
16d
16e
16f
16g
16h
16i
3-(NHCOCH2Cl)
3-(NHCO(CH2)4Br)
3-(NHCOCH2N+Et3)Clꢁ
3-(NHCO(CH2)4N+Et3)Brꢁ
4-((OCH2CH2)3(N+C5H4))Iꢁ
4-((OCH2CH2)3N+Et3)Iꢁ
H
16j
310
200
35
44
6
26
8
22
1.6
3
16k
15a
15b
15c
15d
15e
15f
15g
15h
A polyethylene glycol linker was examined at the 40-
position of the 5-phenyl ring with a quaternary ammo-
nium salt attached to its end as well. Once again these
compounds (15h, 16j and 16k) show greater potency
than the corresponding 40-OH compounds (15d and
16d). It appears that one can substitute a fairly large
substituent on the 5-phenyl ring as long as water solu-
bility is maintained.
3-NO2
3-NH2
4-OMe
4-OH
3-(NHCO(CH2)4Br)
3-(NHCO(CH2)4N+Et3)CF3CO2ꢁ
4-((OCH2CH2)3N+Et3)Iꢁ
Table 1). The benzyl substituted compounds (17a and
17b) exhibited weak inhibition in vitro (IC50>1000
nM). The smaller methyl group (16a–k) was a bit more
active showing moderate to weak in vitro activities
(IC50=320–1200 nM). The secondary sulfonamides
15a–h (R=H) were found to be the most potent com-
pounds in this series as their activities were 20–50 times
more potent than their respective N-methyl analogues
(IC50=3–44 nM). We believe this to be a purely steric
effect due to the low activity when R=benzyl or
R=methyl. The sulfonamido nitrogen may be in close
proximity to the surface of the binding site. Hydrogen
bonding at the sulfonamido nitrogen appears not to
contribute to binding as illustrated by 1,4- and 1,5-
benzothiaepines (2 and 3).
The 1,2-benzothiazepines 1,1-dioxides are a novel class
of ASBT inhibitors that show nanomolar activities in
vitro. Further evaluation is needed in this series in order
to determine the in vivo utility of this novel class of
ASBT inhibitors.
References and Notes
1. Stark, R. M. Am. J. Cardiol. 1995, 78, 13.
2. Lipid Research Clinics Program JAMA 1984, 251, 351.
3. Ast, M.; Frishman, W. H. J. Clin. Pharmacol. 1990, 30, 99.
4. Hofmann, A. F. Clin. Gastroenterol. 1977, 6, 3.
5. Buchwald, H., et al. New Engl. J. Med. 1990, 323, 946.
6. Tollefson, M. B.; Vernier, W. F.; Huang, H.; Chen, F. P.;
Reinhard, E. J.; Beaudry, J.; Keller, B. T.; Reitz, D. B. Bioorg.
Med. Chem. Lett. 2000, 10, 277.
7. Brieaddy, L. E. US Patent 5859240, 1999. Brieaddy, L. E.
US Patent 5910494, 1999. Brieaddy, L. E. US Patent 5998400,
1999.
A modest electronic effect of the lower 5-aryl ring was
observed. The electron withdrawing 30-NO2 group (15b,
IC50=44 nM) had slightly less or comparable activity
than the unsubstituted phenyl ring (15a, IC50=35). The
electron donating 30-NH2 (15c IC50=6 nM) and 40-OH
(15e, IC50=3 nM) showed a 5-10 fold increase in activ-
ity compared to the unsubstituted phenyl ring 15a.
However, the decreased activity of the 40-OMe analogue
(15d, IC50=26 nM) may indicate that the proper place-
ment of the hydrogen as a H-bond donor is required. A
similar trend was noted for tertiary sulfonamide
(R=Me, see compounds 16a–e). However, the 40-OMe
analogue (16d, IC50=570 nM) is equipotent with the 40-
OH analogue (16e, IC50=580 nM) unlike in the sec-
ondary sulfonamides (R=H). The negative interaction
of the N–Me substituent with the transporter changes
8. Stork, G.; Leong, A. Y. W.; Touzin, A. M. J. Org. Chem.
1976, 41, 3491.
9. Sample procedure for the conversion of 7 to 9. To a solution
of 2.0 g (4.25 mmol) of 7 in 10 mL of tetrahydrofuran cooled
to 0 ꢀC was added 8.0 mL of 1.6 M n-butyllithium in hexane.
The reaction mixture was stirred at 0 ꢀC for 30 min. To the
reaction mixture was added 1.9 mL of trimethyl borate and
stirred 10 min at 0 ꢀC then 1 h at room temperature. To the
reaction mixture was added 100 mL of water and enough 5%
hydrochloric acid to bring the solution to a pH of 6–7 then the
volatiles were evaporated. To the aqueous solution was added
100 mL of ethyl acetate then extracted. The ethyl acetate layer
was washed with water (100 mL) and brine (100 mL), dried