Paradisin C: A new CYP3A4 inhibitor from grapefruit juice

Article abstract of DOI:10.1016/S0040-4020(02)00739-1

A new furanocoumarin derivative, paradisin C, was isolated from grapefruit juice as an inhibitor of cytochrome P450 (CYP) 3A4. Its stereochemistry was elucidated by spectroscopic methods. The stereochemistries of 17,18-dihydroxybergamottin and 17-epoxybergamottin were also elucidated.

Full text of DOI:10.1016/S0040-4020(02)00739-1

Tetrahedron 58 (2002) 6631–6635
Paradisin C: a new CYP3A4 inhibitor from grapefruit juice
a
a
a
a
Tomihisa Ohta,a Takuro Maruyama, Minoru Nagahashi, Yasuyo Miyamoto, Shinzo Hosoi,
,
*
Fumiyuki Kiuchi,a Yasushi Yamazoeb and Sachiko Tsukamotoa
aFaculty of Pharmaceutical Sciences, Kanazawa University, 13-1 Takara-machi, Kanazawa 920-0934, Japan
bGraduate School of Pharmaceutical Sciences, Tohoku University, Aoba Aramaki, Aoba-ku, Sendai 980-8578, Japan
Received 8 April 2002; accepted 25 June 2002
Abstract—A new furanocoumarin derivative, paradisin C, was isolated from grapefruit juice as an inhibitor of cytochrome P450 (CYP)
3A4. Its stereochemistry was elucidated by spectroscopic methods. The stereochemistries of 17,18-dihydroxybergamottin and
17-epoxybergamottin were also elucidated. q 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
of two furanocoumarin dimers, GF-I-1 (1) and GF-I-4 (2),
newly named paradisins A and B, respectively, from
grapefruit juice3–6 and bisalkaloids from white pepper.7,8
Recently, we found new CYP inhibitors in which a semi-
synthetic 17,18-dihydroxybergamottin caproate having a
more stable and simpler structure than 1 and 2, exhibited
comparable activity.9 This paper describes the isolation,
structure determination, and CYP inhibitory activity of a new
furanocoumarin dimer, paradisin C (3),10 along with the eluci-
dation of the absolute stereochemistries of 17,18-dihydroxy-
bergamottin (4)11 and 17-epoxybergamottin (5)12 (Chart 1).
Cytochrome P450 (CYP) enzymes are recognized to be
responsible for drug metabolism, degradation of xeno-
biotics, and carcinogenesis. Concomitant oral adminis-
tration of grapefruit juice affected the bioavailability of
dihydropyridine-type calcium channel blockers, such as
felodipine and nifedipine,1 and similar phenomena in
pharmacokinetics have been reported for various clinically
important drugs. In the course of our study on CYP3A42
inhibitors in the diet, we have already reported the isolation
Chart 1.
Keywords: grapefruit juice; paradisin; furanocoumarin; CYP3A4 inhibition; absolute stereochemistry.
*
Corresponding author. Tel./fax: þ81-76-234-4417; e-mail: ohta@dbs.p.kanazawa-u.ac.jp
0040–4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)00739-1

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T. Ohta et al. / Tetrahedron 58 (2002) 6631–6635
Table 1. NMR spectral data for paradisin C (3) in CDCl3
dH
dC
HMBC
dH
dC
HMBC
20
30
40
50
60
70
80
2
161.3 s
112.6 d
139.5 d
148.9 s
114.1 s
158.1 s
94.3 d
117.6 s
116.6 d
124.7 d
147.8 s
113.3 s
156.5 s
94.5 d
C-20, C-100
C-30, C-50, C-90
3
6.26 (1H, d, 9.8)
8.14 (1H, d, 9.8)
C-2, C-10
5.59 (1H, d, 9.8)
7.22 (1H, d, 9.8)
4
C-2, C-5, C-9
C-7, C-9, C-10
5
6
7
C-60, C-70, C-90, C-100
8
7.16 (1H, s)
6.81 (1H, s)
90
9
152.6 s
107.5 s
69.6 t
150.5 s
108.0 s
69.5 t
100
110
120
130
140
150
10
11
12
13
14
15
C-50, C-120, C-130
C-140, C-150
4.94 (2H, d, 7.8)
5.58 (1H, t, 7.8)
C-5, C-12, C-13
C-14, C-15
4.80 (2H, d, 7.8)
5.54 (1H, t, 7.8)
119.6 d
141.9 s
16.7 q
120.2 d
141.9 s
16.3 q
C-120, C-130, C-150
C-120, C-130
1.71 (3H, s)
2.32 (1H, m)
C-12, C-13, C-15
C-12, C-13
1.61 (3H, s)
2.26 (1H, m)
36.4 t
36.4 t
2.21 (1H, m)
1.72 (1H, m)
2.16 (1H, m)
1.57 (1H, m)
160
16
27.2 t
C-13, C-15
29.1 t
1.57 (1H, m)
4.24 (1H, dd, 3.4, 9.8)
1.40 (1H, m)
3.15 (1H, dd, 2.6, 10.5)
170
180
190
200
b0
17
18
19
20
b
82.6 d
82.7 s
77.6 d
73.0 s
C-170, C-180, C-200
C-170, C-180, C-190
C-60, C-70, C-c0
1.47 (3H, s)
22.6 q
26.4 q
144.9 d
105.0 d
C-17, C-18, C-20
C-17, C-18, C-19
C-6, C-7, C-c
1.13 (3H, s)
23.0 q
26.5 q
143.3 d
104.7 d
1.20 (3H, s)
1.15 (3H, s)
7.59 (1H, d, 2.4)
6.94 (1H, d, 2.4)
7.44 (1H, d, 2.4)
6.80 (1H, d, 2.4)
c0
C-60, C-70, C-b0
c
C-6, C-7, C-b
2. Results and discussion
J¼9.8 Hz), 7.44 (d, J¼2.4 Hz), 7.59 (d, J¼2.4 Hz), and 8.14
(d, J¼9.8 Hz)) (Table 1), which indicated the presence of
two O-prenylfurocoumarin moieties. The 13C NMR spec-
trum of 3 (Table 1) was almost superimposable on those of
1 and 2 except for the presence of a quaternary carbon at d
117.6 (C-20) instead of a carbonyl carbon. Interpretation of
the HMBC spectrum confirmed that 3 was composed of
two O-prenylfurocoumarin moieties (Fig. 1). HMBC
correlation, d 5.59 (H-30)/d 117.6 (C-20) (Fig. 1), and NOE
correlation between H-30 and H3-20 (Fig. 2) suggested the
presence of an orthoester structure in 3. The acid hydrolysis
of 3 (10.0 mg) afforded 17,18-dihydroxybergamottin (4,
4.0 mg), 17-ketobergamottin (6, 1.0 mg),12 and 3 (2.0 mg)
which supported the gross structure of 3. During the
hydrolysis of 3, partial dehydration of 4 may be occurred
to afford 6. The compound 4 was led to 17-O-R-(þ)-MTPA
ester (4r), whose NMR data were identical to those of
the corresponding ester with 17R-dihydroxybergamottin,
indicating 17R,170R-configuration of 3. Thereby, together
with the result from the NOESY correlation (Fig. 2),
20S-configuration of 3 was established.
2.1. Isolation and structure elucidation of paradisin C (3)
Grapefruit juice (12 L) was extracted with hexane/EtOAc
(1:1). The concentrated extract (1.2 g) was purified by silica
gel (hexane/EtOAc) and ODS chromatography to afford
a new furanocoumarin derivative paradisin C (3, 2.0 mg,
0.17% from the extract) as well as known paradisins A (1)
and B (2) and 17,18-dihydroxybergamottin (4).
The FAB mass spectrum of paradisin C (3) showed a
pseudomolecular ion peak at m/z 727 [MþH]þ and the
formula of C42H46O11 was established by HRFABMS. The
1H NMR spectrum in CDCl3 showed six singlet methyl
(d 1.13, 1.15, 1.20, 1.47, 1.61, and 1.71), two oxymethylene
(d 4.80 (d, J¼7.8 Hz) and 4.94 (d, J¼7.8 Hz)), two oxy-
methine (d 3.15 (dd, J¼2.6, 10.5 Hz) and 4.24 (dd, J¼3.4,
9.8 Hz)), 12 olefinic signals (d 5.54 (t, J¼7.8 Hz), 5.58
(t, J¼7.8 Hz), 5.59 (d, J¼9.8 Hz), 6.26 (d, J¼9.8 Hz), 6.80
(d, J¼2.4 Hz), 6.81 (s), 6.94 (d, J¼2.4 Hz), 7.16 (s), 7.22 (d,
Figure 1. COSY (bold lines) and HMBC (arrows) correlations observed for paradisin C (3).

T. Ohta et al. / Tetrahedron 58 (2002) 6631–6635
6633
By means of the inhibitory effect of drug metabolizing
enzyme CYP3A4, administration of grapefruit juice could
reduce the drug dose and lead to cost-savings for patients.
Elucidation of the interaction between CYP3A4 and the
inhibitors may be an interesting subject in the pharmaco-
kinetics of clinically used drugs.
Figure 2. NOE correlations observed for paradisin C (3).
2.2. Absolute stereochemistry of 17,18-dihydroxy-
bergamottin (4) and 17-epoxybergamottin (5)
3. Experimental
3.1. General
The structures of 17,18-dihydroxybergamottin (4)11 and
17-epoxybergamottin (5)12 were reported while the absolute
stereochemistry remained undetermined. Here, we establish
the absolute configurations of the chiral centers of the
compounds.
Optical rotations were determined with a HORIBA SEPA-
300 high sensitive polarimeter. UV spectrum was measured
on a SHIMADZU UV-1600 UV-visible spectrophotometer.
IR spectrum was recorded on a SHIMADZU IR-460
infrared spectrophotometer. NMR spectra were recorded
on a JEOL GSX-500 NMR spectrometer in CDCl3. All
chemical shifts were reported with respect to TMS. Mass
spectra were measured on a JEOL SX-102 mass
spectrometer.
3.2. Extraction and isolation
Grapefruit juice (12 L) was extracted with hexane/EtOAc
(1:1). The concentrated extract (1.2 g) was purified by silica
gel (hexane/EtOAc) and ODS (82% MeOH/H2O) chroma-
tography to afford known furanocoumarin derivatives,
paradisins A (1, 5.0 mg, 0.42% from the extract) and B (2,
15.0 mg, 1.3%), bergamottin (7, 25.2 mg, 2.1%), and a
crude fraction (15.0 mg). The crude fraction was purified
by ODS HPLC (95% MeOH/H2O) to afford a new
furanocoumarin derivative, paradisin C (3, 2.0 mg,
0.17%). 17,18-Dihydroxybergamottin (4) and 17-epoxy-
bergamottin (5, 99.8 mg, 1.0%) isolated from grapefruit
oil14 were used in this experiment.
Figure 3. Application of modified Mosher’s method to 17,18-dihydrox-
ybergamottin (4).
17,18-Dihydroxybergamottin (4) was isolated from both
grapefruit juice and its peel oil, while 17-epoxybergamottin
(5) was only from the peel oil. The configuration at C-17 of
4 was determined by the Mosher method (Fig. 3).13 The
chemical shift differences for 17-(R )- and 17-(S)-MTPA
esters of 4 indicated 17R configuration. The absolute
stereochemistry of 17-epoxybergamottin (5) was deter-
mined by comparison of the optical rotation of synthetic
17R-epoxybergamottin (17R-5). Bergamottin (7) was con-
verted to 17S,18-dihydroxybergamottin (17S-4) and then to
17R-epoxybergamottin (17R-5) following the mesylation
(Scheme 1). Optical rotation of the synthetic 17R-5
([a ]D¼þ4.68) was consistent with that of the natural 5
([a ]D¼þ5.38). Thus, 17-configuration of 5 from the
grapefruit peel oil was established as R.
3.2.1. Paradisin C (3). A colorless solid. [a]2D5¼2178 (c
0.12, CHCl3). UV (MeOH) lmax (log 1) 225 (4.3), 245
(5.7), 267 (3.2), 311 nm (2.0). IR (CHCl3) nmax 3581, 1723,
1627, 1608, 1582, 1140, 1080 cm21 1H and 13C NMR
.
(CDCl3) see Table 1. FABMS (positive) m/z 727 [MþH]þ;
HRFABMS (positive) m/z 727.3115 (C42H47O11,
20.4 mmu).
D
3.2.2. Acid hydrolysis of paradisin C (3). A solution of
3 (10.0 mg) in dimethoxyethane (210 mL) was added to
0.01N HCl (150 mL), and the mixture was kept at room
temperature for 4 h. The solvent was evaporated, and the
residue was purified by ODS HPLC (70% MeOH/H2O) to
afford 17,18-dihydroxybergamottin (4, 4.0 mg), 17-keto-
bergamottin (6, 1.0 mg), and 3 (2.0 mg).
2.3. CYP3A4 inhibitory activity of paradisin C (3)
CYP activity was based on nifedipine oxidation. Paradisin C
(3) showed moderate CYP3A4 inhibitory activity with IC50
values of 1.0 mM compared to paradisins A (1) and B (2)
(IC50, 0.07 and 0.07 mM).
Scheme 1. (i) 3.0 equiv. K3Fe(CN)6, 3.0 equiv. K2CO3, 1.0 equiv. CH3SO2NH2, 0.025 equiv. (DHQ)2-PHAL, H2O, 08C; (ii) 0.005 equiv. OsO4, t-BuOH, H2O,
78C, 21 h; (iii) 12 equiv. Na2SO3, 78C, 30 min; (iv) 1.2 equiv. MsCl, pyridine, rt, 3 h; (v) 1.2 equiv. MsCl, rt, 4 h; (vi) 2.0 equiv. DBU, CH2Cl2, rt, 1 h;
(vii) 2.0 equiv. DBU, rt, 2 h.

6634
1
T. Ohta et al. / Tetrahedron 58 (2002) 6631–6635
4: H NMR (CDCl3) d 1.16 (3H, s, H3-19), 1.20 (3H, s,
H3-20), 1.45 (1H, m, H-16), 1.59 (1H, m, H-16), 1.70 (3H, s,
H3-14), 2.15 (1H, m, H-15), 2.36 (1H, m, H-15), 3.31 (1H, d,
J¼8.0 Hz, H-17), 4.94 (2H, d, J¼6.8 Hz, H2-11), 5.59 (1H,
t, J¼6.8 Hz, H-12), 6.26 (1H, d, J¼9.8 Hz, H-3), 6.94 (1H,
d, J¼1.5 Hz, H-c), 7.14 (1H, s, H-8), 7.59 (1H, d, J¼1.5 Hz,
H-b), 8.14 (1H, d, J¼9.8 Hz, H-4). EI-MS m/z 372 [M]þ.
K2CO3 (65.6 mg, 3.0 mol equiv.), CH3SO2NH2 (15.1 mg,
1.0 mol equiv.), and (DHQ)2-PHAL (3.1 mg, 0.025 mol
equiv.) in water (3.5 mL) at 08C was added bergamottion
(7, 58.9 mg) and OsO4 (5.3 mL of 3.8% aqueous solution,
0.005 mol equiv.) in t-BuOH (3.5 mL). The mixture was
stirred at 78C for 21 h. To this was added Na2SO3 (250 mg,
12 mol equiv.) and stirred at this temperature for 30 min.
The product was extracted with EtOAc (15 mL£3), and the
organic layer was washed with brine, dried over Na2SO4,
and concentrated to afford a residue (51.9 mg). Purification
over silica gel using hexane/EtOAc (1:1) gave 17S,18-
dihydroxybergamottin (17S-4, 30.2 mg, 86% ee) of which
solution in EtOAc gave colorless needles (17S-4, 7.0 mg,
92% ee). Enantiomeric excess (ee) was analyzed by a chiral
HPLC.
1
6: H NMR (CDCl3) d 1.10 (6H, d, J¼6.8 Hz, H3-19 and
H3-20), 1.70 (3H, s, H3-14), 2.34 (2H, t, J¼7.3 Hz, H2-15),
2.58 (2H, t, J¼7.3 Hz, H2-16), 2.60 (1H, septet, J¼6.8 Hz,
H-18), 4.93 (2H, d, J¼6.8 Hz, H2-11), 5.53 (1H, t, J¼
6.8 Hz, H-12), 6.28 (1H, d, J¼9.8 Hz, H-3), 6.94 (1H, d,
J¼2.4 Hz, H-c), 7.17 (1H, s, H-8), 7.60 (1H, d, J¼2.4 Hz,
H-b), 8.15 (1H, d, J¼9.8 Hz, H-4). FABMS (positive) m/z
355 [MþH]þ.
17S-4: mp 60–688; 1H NMR (CDCl3) d 1.17 (3H, s, H3-19),
1.21 (3H, s, H3-20), 1.46 (1H, m, H-16), 1.60 (1H, m, H-16),
1.70 (3H, s, H3-14), 2.16 (1H, m, H-15), 2.37 (1H, m, H-15),
3.22 (1H, d, J¼9.3 Hz, H-17), 4.94 (2H, d, J¼6.8 Hz,
H2-11), 5.59 (1H, t, J¼6.8 Hz, H-12), 6.26 (1H, d, J¼
9.8 Hz, H-3), 6.95 (1H, d, J¼2.4 Hz, H-c), 7.13 (1H, s, H-8),
7.60 (1H, d, J¼2.4 Hz, H-b), 8.15 (1H, d, J¼9.8 Hz, H-4).
FABMS (positive) m/z 373 [MþH]þ.
A solution of 4 (4.1 mg) derived from 3 in THF (1.0 mL)
was treated with (S )-MTPA chloride (6.0 mL) in the
presence of DMAP (5.0 mg) at room temperature for 23 h.
After evaporation, the residue was purified by silica gel
chromatography (hexane/EtOAc, 3:1) and ODS HPLC
(82% MeOH/H2O) to afford (R )-MTPA ester (4r, 3.1 mg).
1
4r: H NMR (CDCl3) d 1.15 (3H, s, H3-19), 1.20 (3H, s,
H3-20), 1.61 (3H, s, H3-14), 1.62 (1H, m, H-16), 1.75 (1H,
m, H-16), 1.97 (2H, t, J¼7.3 Hz, H2-15), 4.92 (2H, d, J¼
6.8 Hz, H2-11), 4.97 (1H, dd, J¼10.3, 2.4 Hz, H-17), 5.47
(1H, t, J¼6.8 Hz, H-12), 6.28 (1H, d, J¼9.8 Hz, H-3), 6.94
(1H, d, J¼2.4 Hz, H-c), 7.17 (1H, s, H-8), 7.60 (1H, d, J¼
2.4 Hz, H-b), 8.16 (1H, d, J¼9.8 Hz, H-4). FABMS
(positive) m/z 589 [MþH]þ.
A solution of 17S-4 (20.0 mg) in pyridine (200 mL) was
added to MsCl (5.0 mL, 1.2 mol equiv.). The mixture was
stirred at room temperature for 3 h, and to this was added
additional MsCl (5.0 mL, 1.2 mol equiv.). After being
stirred at room temperature for 4 h, a solution of DBU
(16.2 mL, 2.0 mol equiv.) in CH2Cl2 (200 mL) was added.
The mixture was stirred at room temperature for 1 h, and to
this was added additional DBU (16.2 mL, 2.0 mol equiv.).
The mixture was stirred at room temperature for 2 h, and the
solution was applied on silica gel chromatography (CHCl3),
followed by HPLC with gel filtration column (CHCl3) to
afford (R )-epoxybergamottin (17R-5, 4.5 mg).
3.2.3. MTPA ester of dihydroxybergamottin (4). A
solution of 4 (4.0 mg) in THF (1.0 mL) was treated with
(S )-MTPA chloride (6.1 mL) in the presence of DMAP
(5.3 mg) at room temperature for 32 h. After evaporation,
the residue was purified by silica gel chromatography
(hexane/EtOAc, 3:1) and ODS HPLC (82% MeOH/H2O)
to afford (R )-MTPA ester (4r, 2.0 mg). (S)-MTPA ester
(4 s, 1.5 mg) was prepared by the same procedure as that for
(R )-MTPA ester (4 s).
1
17R-5: [a ]D¼þ4.68 (c 0.18, CHCl3). H NMR (CDCl3) d
1.27 (3H, s, H3-19), 1.31 (3H, s, H3-20), 1.59–1.72 (2H, m,
H2-16), 1.73 (3H, s, H3-14), 2.16–2.31 (2H, m, H2-15), 2.70
(1H, dd, J¼7.3, 5.4 Hz, H-17), 4.96 (2H, d, J¼6.8 Hz,
H2-11), 5.60 (1H, t, J¼6.8 Hz, H-12), 6.27 (1H, d, J¼
9.8 Hz, H-3), 6.95 (1H, d, J¼2.4 Hz, H-c), 7.15 (1H, s, H-8),
7.60 (1H, d, J¼2.4 Hz, H-b), 8.15 (1H, d, J¼9.8 Hz, H-4).
EI-MS (positive) m/z 354 [M]þ.
1
4r: H NMR (CDCl3) d 1.15 (3H, s, H3-19), 1.20 (3H, s,
H3-20), 1.61 (3H, s, H3-14), 1.62 (1H, m, H-16), 1.75 (1H,
m, H-16), 1.97 (2H, t, J¼7.3 Hz, H2-15), 4.92 (2H, d,
J¼6.8 Hz, H2-11), 4.97 (1H, dd, J¼10.3, 2.4 Hz, H-17),
5.47 (1H, t, J¼6.8 Hz, H-12), 6.28 (1H, d, J¼9.8 Hz, H-3),
6.94 (1H, d, J¼2.4 Hz, H-c), 7.17 (1H, s, H-8), 7.60 (1H, d,
J¼2.4 Hz, H-b), 8.16 (1H, d, J¼9.8 Hz, H-4). FABMS
(positive) m/z 589 [MþH]þ.
3.3. CYP inhibition assay
CYP activity was based on nifedipine oxidation. Various
amounts (0–10 mM, final concentration) of samples in 1 mL
of DMSO were added to 192 mL of solution containing
100 mM phosphate buffer (pH 7.4) containing 50 mM
nifedipine (Wako Pure Chemical Industries, Ltd (Osaka,
Japan)), 5 mM glucose-6-phosphate (Oriental Yeast Co.,
Ltd (Tokyo, Japan)), 0.5 mM b-NADPþ (Oriental Yeast
Co., Ltd), 0.5 mM MgCl2, and 4.3 mg/mL glucose-6-
phosphate dehydrogenase (Oriental Yeast Co., Ltd) and
incubated at 378C for 5 min. CYP3A4 (Gentest Co.
(Woburn, MA, USA)) was also preincubated in 7 mL of
the buffer at 378C for 5 min and added to the sample
solution. After the incubation at 378C for 1 h, the reaction
was quenched by the addition of 100 mL of MeOH. After
1
4s: H NMR (CDCl3) d 1.14 (3H, s, H3-19), 1.17 (3H, s,
H3-20), 1.66 (3H, s, H3-14), 1.72 (1H, m, H-16), 1.85 (1H,
m, H-16), 2.07 (2H, t, J¼7.8 Hz, H2-15), 4.94 (2H, d,
J¼6.8 Hz, H2-11), 4.97 (1H, dd, J¼9.8, 2.0 Hz, H-17), 5.51
(1H, t, J¼6.8 Hz, H-12), 6.27 (1H, d, J¼9.8 Hz, H-3), 6.95
(1H, d, J¼2.4 Hz, H-c), 7.17 (1H, s, H-8), 7.60 (1H, d,
J¼2.4 Hz, H-b), 8.17 (1H, d, J¼9.8 Hz, H-4). FABMS
(positive) m/z 589 [MþH]þ.
3.2.4. Preparation of (R )-17-epoxybergamottin (17R-5).
To a solution of K3Fe(CN)6 (156.4 mg, 3.0 mol equiv.),

T. Ohta et al. / Tetrahedron 58 (2002) 6631–6635
6635
3. Fukuda, K.; Ohta, T.; Oshima, Y.; Ohashi, N.; Yoshikawa, M.;
Yamazoe, Y. Pharmacogenetics 1997, 7, 391–396.
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adding 3.7 mg of 6-methoxycarbonyl-5-methyl-7-(2-nitro-
phenyl)-4,7-dihydrofuro[3,4-b]pyridin-1-(3H )-one in 1 mL
of DMSO as an internal standard, the reaction mixture was
extracted with 1 mL of ether, and the ether layer was
evaporated. The residue was dissolved in 100 mL of MeOH,
and an aliquot (20 mL) was analyzed by reverse phase
HPLC (column, TSK-gel ODS-120T, 4.6 mm i.d.£150 mm;
mobile phase, 64% MeOH/H2O; flow rate, 1.0 mL/min;
detection, UV 254 nm); retention times: 2.9 min for the
internal standard, 4.0 min for the nifedipine metabolite
(nifedipine pyridine), and 5.5 min for nifedipine. The value
of IC50, the concentration required for 50% inhibition of
CYP3A4 activity, was calculated from the data of duplicate
measurements.
6. Ohta, T.; Nagahashi, M.; Miyamoto, Y.; Hosoi, S.; Maruyama,
T.; Kiuchi, F.; Yamazoe, Y. Symposium Papers of the 41th
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Acknowledgments
10. The structure of paradisin C (3) has been previously shown as
GF-I-6 without spectal data.5
We thank Kirin Beverage Co. (Japan), for a generous gift of
grapefruit juice.
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microsomes is reported to be CYP3A4,15,16 and 50% of
clinically important drugs has been metabolized by CYP3A4.17