Discovery of novel retinoic acid receptor agonists having potent antiproliferative activity in cervical cancer cells

Article abstract of DOI:10.1021/jm960285j

Retinoic acid receptor (RAR) active retinoids have proven therapeutically useful for treating certain cancers and dermatological diseases. Herein, we describe the discovery of two new RAR active trienoic acid retinoids, (2E,4E,6E)-7-(3,5-di-tert-butylphen

Full text of DOI:10.1021/jm960285j

J . Med. Chem. 1996, 39, 2659-2663
2659
Expedited Articles
Discover y of Novel Retin oic Acid Recep tor Agon ists Ha vin g P oten t
An tip r olifer a tive Activity in Cer vica l Ca n cer Cells
Lin Zhang,† Alex M. Nadzan,† Richard A. Heyman,‡ Deborah L. Love,‡ Dale E. Mais,§ Glenn Croston,
William W. Lamph,‡ and Marcus F. Boehm*,†
Departments of Retinoid Chemistry, Retinoid Research, Endocrine Research, and New Leads Discovery, Ligand
Pharmaceuticals, Inc., 10255 Science Center Drive, San Diego, California 92121
Received April 15, 1996X
Retinoic acid receptor (RAR) active retinoids have proven therapeutically useful for treating
certain cancers and dermatological diseases. Herein, we describe the discovery of two new
RAR active trienoic acid retinoids, (2E,4E,6E)-7-(3,5-di-tert-butylphenyl)-3-methylocta-2,4,6-
trienoic acid (10a , ALRT1550) and (2E,4E,6Z)-7-(3,5-di-tert-butylphenyl)-3-methylocta-2,4,6-
trienoic acid (10b, LG100567). ALRT1550 is a RAR selective retinoid which exhibits exceptional
potency in both competitive binding and cotransfection assays. Moreover, it is the most potent
antiproliferative retinoid described to date and thus has implications for the treatment of certain
cancers. LG100567 is a potent panagonist which activates both RARs and retinoid X receptors.
Ch a r t 1
Retinoids have found utility for treatment of numer-
ous diseases including acne, psoriasis, and cancer.1-3
The therapeutic effects of retinoids result from their
ability to control abnormal cellular processes by modu-
lating cell differentiation, inhibiting cell proliferation,
and regulating apoptosis. These processes are initiated
by the formation of an active ligand-receptor complex
with one or more of six intracellular (IR) retinoid
receptors, RARR,â,γ and RXRR,â,γ.4 This produces
transcriptional activation which results in physiological
responses. Interestingly, in addition to positively regu-
lating gene expression, retinoids may also regulate the
expression of certain genes by inhibiting the enhancer
effects of transcription factors such as AP-1,5-7
a
transcription factor complex composed of the oncogenes
Fos and J un.
Currently, several retinoids are marketed or in clini-
cal trials for treatment of cancer and skin disease.1,2
These include ATRA (all-trans-retinoic acid), 13-cis-RA
(13-cis-retinoic acid), etretinate, 9-cis-RA (9-cis-retinoic
acid), Tazarotene,8 and Targretin (LGD1069) (see Chart
1).9,10 Apart from Targretin, an RXR selective retinoid,
all of these compounds have significant RAR activity.
Unfortunately, compounds such as ATRA, 13-cis-RA and
etretinate have the potential liability of exhibiting
hypervitaminosis-A-like side effects with chronic treat-
ment.11-13 In addition, chronic treatment with ATRA
results in a rapid induction of metabolism14 and,
subsequently, reduced therapeutic efficacy.
The promising clinical results experienced by acute
promyelocytic leukemia (APL) patients15,16 treated with
ATRA has inspired continued research to identify other
RAR active agents for the treatment of cancer. Our goal
was to identify novel analogs of ATRA and 9-cis-RA
which exhibit (1) similar receptor profiles, (2) antipro-
liferative activity against a broad spectrum of cancer
cells, and (3) increased chemical and metabolic stability.
Additionally, it is desirable to obtain compounds which
show an increase in therapeutic index. Our synthetic
strategy was to substitute the â-ionene moiety 1 (see
Figure 1) of ATRA and 9-cis-RA with a lipophilic
bioisostere such as a dialkylphenyl group. The utility
of such bioisosteres has been demonstrated by Shudo
et al.17,18 with the design of synthetic retinoids 3 and 4
which contain a di-tert-butylphenyl moiety 2. These
compounds were effective in differentiating human
leukemia (HL-60) cells.19 Substitution of the â-ionene
moiety 1 of ATRA and 9-cis-RA with a di-tert-butyl-
phenyl function would eliminate the oxidizable C-12
allylic position (see Chart 1 for numbering) and shorten
the side chain by one conjugated double bond. Thus,
we hypothesized that dialkylphenyl-substituted analogs
of ATRA and 9-cis-RA may result in compounds with
biological activity against cancer cells as well as in-
creased chemical and metabolic stability.
* Author to whom correspondence should be addressed.
† Department of Retinoid Chemistry.
‡ Department of Retinoid Research.
§ Department of Endocrine Research.
Department of New Leads Discovery.
X Abstract published in Advance ACS Abstracts, J une 15, 1996.
S0022-2623(96)00285-3 CCC: $12.00 © 1996 American Chemical Society

2660 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 14
Zhang et al.
the analogues were determined by application of the
Cheng-Prussof equation.21 Cotransfection assays were
performed as described,8,22-24 and the values (EC50) are
reported in nM.
Cell Cu ltu r e. ME-180 cells (ATCC HTB 33)25 were
obtained from the American Type Culture Collection
(ATCC, Rockville, MD).
In cor p or a tion of [5′-3H]Th ym id in e. The method
used for determining radiolabeled thymidine incorpora-
tion was adapted from the procedure described by
Shrivastav et al.26
Biologica l R esu lt s. Compounds ALRT1550, LG-
100567, ATRA, and 9-cis-RA were evaluated in the
competitive binding assay which characterizes the
ligand’s ability to bind directly to each of the six retinoid
receptor subtypes and the cotransfection assay which
measures the ability of compounds to activate gene
expression at each of the six retinoid receptors and
reflects the compound’s functional activity. Ki and EC50
values for ALRT1550 and LG100567, shown in com-
parison to ATRA and 9-cis-RA, are reported in Table 1
for the six known retinoid receptors: RARR, RARâ,
RARγ, RXRR, RXRâ, and RXRγ. ALRT1550, like ATRA,
is RAR selective; however, unlike ATRA, which is only
15-50 times more potent at the RARs than at the RXRs,
ALRT1550 is 100-800 more potent in the binding assay
and at least 2000 times more potent in the cotransfec-
tion assay to the RARs than to the RXRs. In addition
it is at least 10-fold more potent than ATRA at the RARs
in both assays. Although weak binding was observed
at the RXRs for ALRT1550, no RXR activity was
measured in the cotransfection assay at up to 1 µM.
Further, ALRT1550 is not an antagonist of Targretin
at the RXRs in the cotransfection assay (data not
shown). In contrast, although LG100567 is active at
the RARs, the binding and cotransfection values are at
least 50 times less than ALRT1550. LG100567 is also
active at the RXRs and exhibits a “pan-agonist” receptor
profile (active at all six receptors) that is similar to that
of 9-cis-RA in the cotransfection and binding assays.
Interestingly, both LG100567 and 9-cis-RA exhibit
somewhat higher binding affinities for the RXRs than
for the RARs.
These retinoids were further examined for their
antiproliferative activity in human cervical carcinoma
cells (ME180) (shown in Figure 2). This assay measures
the extent of incorporation of [3H]thymidine into DNA
with increasing concentrations of the four retinoids as
compared to untreated cells. All four retinoids exhibit
concentration-dependent inhibition of [3H]thymidine
incorporation into DNA. The IC50 values for LG100567,
ALRT1550, ATRA, and 9-cis-RA are 20, 1, 300, and 500
nM, respectively, in this assay. On the basis of these
values, ALRT1550 is 300 times more potent than ATRA
and LG100567 is 25 times more potent than 9-cis-RA
in their ability to inhibit cellular proliferation.
F igu r e 1.
Herein, we describe the synthesis and biological
activity of two new retinoids, ALRT1550 (10a , Scheme
1) and LG100567 (10b). These compounds are analogs
of ATRA and 9-cis-RA and differ from the parent
compounds by having a 3,5-di-tert-butyl phenyl group
in place of the â-ionene moiety. Our data indicate that
ALRT1550 is one of the most potent and RAR selective
retinoids discovered to date. It is 10-100 times more
potent than ATRA in competitive binding and cotrans-
fection assays and 300 times more potent than ATRA
in its ability to inhibit cellular proliferation in cervical
carcinoma cells.
Ch em istr y
ALRT1550 (10a ) and LG100567 (10b) were synthe-
sized from 3,5-di-tert-butylbenzoic acid (5) in five steps
as shown in Scheme 1. Benzoic acid 5 was treated with
2 equiv of methyllithium at -78 °C to give acetophenone
6. Condensation of the acetophenone 6 with the anion
of diethyl (cyanomethyl)phosphonate resulted in a 10:1
mixture of two isomeric nitrile alkenes, 7a (2E) and 7b
(2Z), which were separated by preparative thin-layer
chromatography (PTLC). Nitrile 7a was treated with
2 equiv of diisobutylaluminum hydride (DIBAL) to
provide aldehyde 8a . Horner-Emmons condensation
of the aldehyde 8a with diethyl[3-(ethoxycarbonyl)-2-
methylprop-2-enyl]phosphonyl anion gave the ethyl
trienoate 9a . Saponification (KOH, MeOH) of 9a gave
the carboxylic acid 10a (ALRT1550). Similarly, nitrile
7b was converted to the triene carboxylic acid 10b
(LG100567). ALRT1550 and LG100567 were purified
by crystallization from EtOH as fine, pale yellow
needles. Analytical data, including high-resolution
mass spectra, 1H-NMR spectra, and elemental analysis,
are consistent with the structures assigned for
ALRT1550 and LG100567. The stereochemistry of
aldehydes 8a and 8b was unambiguously assigned from
nuclear Overhauser enhancement (NOE) experiments.
A 6% NOE in the intensity of the olefinic proton was
observed upon irradiation of the methyl group in 8b.
No such enhancement was observed for 8a . This is
consistent with the assignments for 8a (trans) and 8b
(cis).
Discu ssion
In this study we identified two novel analogs of
retinoic acid, namely, ALRT1550 and LG100567, which
exhibit potent retinoid activity in binding and cotrans-
fection assays and inhibit growth of ME180 cancer cells.
The structural similarity of these compounds to ATRA
and 9-cis-RA is evident in the configuration of the
olefinic side chain. All four of these retinoids have
Biology
Bin d in g St u d ies a n d Cot r a n sfect ion St u d ies.
Receptor binding assays for RARs and RXRs were
performed in a similar manner as described in Boehm
et al.9 using [3H]-9-cis-RA20 as the radioligand for the
RXRs and [3H]ATRA for the RARs. Ki values (nM) for

Novel Retinoic Acid Receptor Agonists
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 14 2661
Ta ble 1. Competition Binding (Ki)a and Cotransfection (EC50 and Percent Efficacy)b Data
RAR
RXR
compound
ATRA
nM
R
â
γ
R
â
γ
Ki
18.7 ( 1.7
563 ( 30
100
22.3 ( 6.0
304 ( 20
81
1.1 ( 0.1
4.0 ( 0.6
31
63.5 ( 8.5
65 ( 12
39
17.4 ( 1.2
105 ( 8.0
100
10.9 ( 1.4
52 ( 4.6
81
0.7 ( 0.3
2.2 ( 0.7
40
90.4 ( 9.0
24 ( 3.0
45
18.5 ( 1.9
33 ( 6.0
100
20.0 ( 1.9
74 ( 9.0
93
1.9 ( 0.2
0.34 ( 0.04
48
124 ( 18
16 ( 1.0
58
350 ( 3.7
1084 ( 33
100
8.4 ( 0.7
316 ( 19
143
881 ( 9.0
1394 ( 49
100
7.4 ( 0.6
200 ( 16
128
288 ( 6.9
1255 ( 39
100
13.0 ( 1.7
219 ( 13
132
EC50
efficacy
Ki
EC50
efficacy
Ki
EC50
efficacy
Ki
EC50
efficacy
9-cis-RA
ALRT1550
LG100567
223 ( 43
560 ( 130
320 ( 62
NA
NA
NA
4.6 ( 0.6
134 ( 16
56
10.2 ( 3.7
87 ( 44
27
9.3 ( 1.5
77 ( 26
40
a
b
All Ki values are mean ( SEM of an average of four or five experiments with triplicate determinations in baculovirus. All EC50
values were determined from full dose-response curves ranging from 10-12 to 10-5 M in CV-1 cells. Values are represented as the mean
( SEM of at least three separate experiments with triplicate determinations. Percent efficacy is reported relative to ATRA (ATRA )
100%). NA ) no measurable transactivation above the control at 1 µM.
that the receptor selectivity of these compounds is
largely determined by the configuration of the C-6 olefin
bond. The 6E configuration of ATRA and ALRT1550
imparts RAR selectivity, whereas the 6Z configuration
of 9-cis-RA and LG100567 imparts a pan-agonist profile.
On the basis of our experience, we expected the respec-
tive isomer pairs (ATRA/ALRT1550, and 9-cis-RA/
LG100567) to exhibit similar profiles in biological
assays. Indeed, the results presented here demonstrate
that LG100567 shows comparable activity to that of
9-cis-RA in both the binding and cotransfection assays.
Surprisingly, however, comparison of the all-trans-
retinoids reveals that ALRT1550 is significantly more
potent and RAR selective than ATRA in the binding and
cotransfection assays.
F igu r e 2. Antiproliferative effects of various retinoids on ME
Both ALRT1550 and LG100567 are particularly ef-
180 cervical carcinoma cells. The extent of proliferation of ME-
180 cells was determined by incorporation of [3H]thymidine
into DNA. The retinoids were added to appropriate wells at
the concentrations indicated. The amount of incorporated
radioactivity (DPM) was determined by liquid scintillation
counting. The numbers represent the mean disintegrations per
minute of incorporated thymidine from triplicate wells.
fective in the antiproliferative assay against ME-180
cells where ALRT1550 is 300 times more potent than
ATRA and LG100567 is 25 times more potent than 9-cis-
RA. To the best of our knowledge, such a dramatic
increase in activity among similar retinoid isomers is
unprecedented. In the antiproliferative assay AL-
RT1550 is fully efficacious, showing inhibition of growth
similar to that exhibited by ATRA, whereas in the
cotransfection assay the efficacy of ALRT1550 is ap-
proximately one-third to one-half that of ATRA.
methyl groups at the C-3 and C-7 positions as well as
olefins in the E configuration at the C-2 and C-4
positions (see Chart 1 and Scheme 1 for numbering).
From the binding and cotransfection data it is apparent
Sch em e 1

2662 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 14
Zhang et al.
The reaction mixture was stirred for 30 min, followed by
addition of 1.59 g (6.85 mmol) of ketone 6 in 5 mL of dry THF.
After 3 h of stirring, the reaction mixture was quenched with
saturated aqueous NH4Cl (50 mL), and the products were
extracted with ether (2 × 50 mL). The combined ether extract
was washed (water then brine), dried over MgSO4, filtered,
concentrated, and purified by preparative TLC (SiO2, 2.5%
EtOAc-hexanes) to give 1.1 g (4.4 mmol) of the E isomer 7a
and 104 mg (0.4 mmol) of the cis isomer 7b (70% combined
yield). E isomer 7a : TLC (5% EtOAc-95% hexanes) Rf 0.9;
1H-NMR (CDCl3) δ 1.32 (s, 18H, 6(CH3)), 2.49 (s, 3H, CH3),
5.59 (s, 1H, dCH), 7.25 (d, J ) 1 Hz, 2H, Ar-H), 7.50 (d, J )
1 Hz, 1H, Ar-H). Z isomer 7b: TLC (5% EtOAc-95% hexanes)
RXR selective retinoids, such as Targretin, are mini-
mally active or inactive in this assay (data not shown),
suggesting that the mechanism of action may be medi-
ated by transactivation of RARs or possibly via trans-
repression of AP-1-related signaling pathways.7 The
potent antiproliferative activity of ALRT1550 may be
explained by its subnanomolar cotransfection activity
at RARγ based on the observation that retinoid modula-
tion of ME-180 cell growth is regulated by the epidermal
growth factor receptor (EGFR) whose promoter is in
turn regulated by RARγ.27 However, other mechanisms
may contribute to its potent antiproliferative activity
as shown by the negative regulation of AP-1 genes with
ATRA.7
1
Rf 0.8; H-NMR (CDCl3) δ 1.42 (s, 18H, 6(CH3)), 2.31 (s, 3H,
CH3), 5.34 (s, 1H, dCH), 7.39 (d, J ) 1 Hz, 2H, Ar-H), 7.49 (t,
J ) 1 Hz, 1H, Ar-H).
3-(3,5-Di-ter t-bu tylp h en yl)bu t-2-en a l (8a , E isom er ).
To 736 mg (2.89 mmol) of 7a in 5 mL of CH2Cl2 at -78 °C was
added 2.31 mL (3.47 mmol) of a 1.5 M solution of DIBAL in
toluene. After 15 min of stirring at -78 °C, the reaction
mixture was quenched with 10 mL of a saturated aqueous
solution of Rochelle salt. The product was extracted with ether
(2 × 20 mL), washed (water then brine), dried over MgSO4,
filtered, concentrated, and purified by chromatography (SiO2,
3% EtOAc-hexanes) to give 462.3 mg (1.80 mmol) of 8a (62%
yield): TLC (10% EtOAc-90% hexanes) Rf 0.5; 1H-NMR
(CDCl3) δ 1.34 (s, 18H, 6(CH3)), 2.59 (s, 3H, CH3), 6.50 (d, J )
8.0 Hz, 1H, dCH), 7.39 (d, J ) 1 Hz, 2H, Ar-H), 7.51 (t, J ) 1
Hz, 1H, Ar-H), 10.18 (d, J ) 8.0 Hz, 1H, CHO).
3-(3,5-Di-ter t-bu tylp h en yl)bu t-2-en a l (8b, Z isom er ).
The Z isomer 8b was prepared from the corresponding Z
isomer 7b using the same method as described for 8a (80%
yield): TLC (10% EtOAc-90% hexanes) Rf 0.55; 1H-NMR
(CDCl3) δ 1.34 (s, 18H, 6(CH3)), 2.34 (s, 3H, CH3), 6.12 (d, J )
8.0 Hz, 1H, dCH), 7.10 (d, J ) 1 Hz, 2H, Ar-H), 7.46 (t, J ) 1
Hz, 1H, Ar-H), 9.45 (d, J ) 8.0 Hz, 1H, CHO).
Eth yl (2E,4E,6E)-7-(3,5-Di-ter t-bu tylp h en yl)-3-m eth yl-
octa -2,4,6-tr ien oa te (9a ). To 790 mg (3.0 mmol) of triethyl
3-methyl-4-phosphonocrotonate in 8 mL of dry THF at -78
°C was added 1.2 mL of a 2.5 M nBuLi solution in hexanes.
After stirring for 15 min, the solution containing the ylide of
triethyl phosphonocrotonate was added to 258 mg (1.0 mmol)
of the E isomer 8a in 8 mL of dry THF at -78 °C. The reaction
mixture was warmed to room temperature, and quenched with
saturated aqueous NH4Cl (20 mL), and the products were
extracted with ether (2 × 50 mL). The combined ether extract
was washed (water then brine), dried over MgSO4, filtered,
concentrated, and purified by column chromatography (SiO2,
5% EtOAc-hexanes) to give 335 mg (0.91 mmol) of 9a (91%
yield): TLC (5% EtOAc-95% hexanes) Rf 0.78; 1H-NMR
(CDCl3) δ 1.30 (t, J ) 7.7 Hz, 3H, CH2CH3), 1.34 (s, 18H,
6(CH3)), 2.28 (s, 3H, CH3), 2.39 (s, 3H, CH3), 4.17 (m, 2H, CH2-
CH3), 5.82 (s, 1H, dCH), 6.40 (d, J ) 15 Hz, 1H, dCH), 6.54
(d, J ) 12 Hz, 1H, dCH), 7.04 (m, 1H, dCH), 7.21 (d, J ) 1
Hz, 2H, Ar-H), 7.39 (t, J ) 1 Hz, 1H, Ar-H).
Eth yl (2E,4E,6Z)-7-(3,5-Di-ter t-bu tylp h en yl)-3-m eth yl-
octa -2,4,6-tr ien oa te (9b). The 2E,4E,6Z isomer 9b was
prepared in the same manner as the 2E,4E,6E isomer 9a
except that 8b was used instead of the 8a . Compound 9b was
obtained in 90% yield: TLC (5% EtOAc-95% hexanes) Rf 0.82;
1H-NMR (CDCl3) δ 1.27 (t, J ) 7.7 Hz, 3H, CH2CH3), 1.34 (s,
18H, 6(CH3)), 2.17, (s, 3H, CH3), 2.22 (s, 3H, CH3), 4.15 (m,
2H, CH2CH3), 5.74 (s, 1H, dCH), 6.25 (d, J ) 11 Hz, 1H, dCH),
6.27 (d, J ) 15 Hz, 1H, dCH), 7.10 (d, J ) 1 Hz, 2H, Ar-H),
7.37 (t, J ) 1 Hz, 1H, Ar-H).
One further benefit of this structural class of com-
pounds may be their increased chemical and metabolic
stability. Replacement of the â-ionene moiety of ATRA
and 9-cis-RA with the di-tert-butylphenyl function re-
sults in elimination of the oxidizable C-12 allylic position
as well as one less conjugated olefin in the side chain.
As a result, it is likely that these compounds exhibit
increased chemical and metabolic stability over that of
ATRA and 9-cis-RA.
In conclusion, the potent activity of ALRT1550 and
LG100567 in binding, cotransfection, and antiprolifera-
tive assays suggests that these retinoids may provide
significant chemotherapeutic efficacy in vivo. Our
preliminary data indicate that ALRT1550 is highly
efficacious in inhibiting tumor growth of a human head
and neck carcinoma in an in vivo xenograft mouse
model.28 Moreover, we believe that exceptionally potent
RAR modulators such as ALRT1550 may provide sub-
stantial chemotherapeutic efficacy upon short-term
administration and thus may reduce the incidence of
hypervitaminosis-A, which is often observed with chronic
administration of retinoids. This assumption remains
to be evaluated in further in vivo studies. On the basis
of the data presented here and the activity in numerous
other in vitro and in vivo assays (to be presented in
future reports), ALRT1550 has recently been selected
as a clinical candidate for the acute treatment of various
cancers.
Exp er im en ta l Section
Unless otherwise stated, all reactions were carried out under
a nitrogen atmosphere. The organic solvents were purchased
from Fisher Scientific. TLC was performed with Merck
Kieselgel 60 F-254 plates. 1H-NMR spectra were determined
on a Bruker 400 MHz instrument. Mass spectra were recorded
on a Hewlett-Packard GCMS Model 5890 mass spectrometer.
Melting points were obtained with Mettler FP62 and Mel-
Temp II instruments. Elemental analyses were performed on
a modified Coulometrics Carbon Analyzer Model 120 and a
Carlo Erba Nitrogen Analyzer Model NA1500.
3,5-Di-ter t-bu tyla cetop h en on e (6). To 20.0 g (85.5 mmol)
of 3,5-di-tert-butylbenzoic acid 2 in 100 mL of dry THF at -78
°C was added 94.0 mL (188.0 mmol) of a 2 N ether solution of
MeLi. The reaction mixture was warmed slowly to room
temperature, stirred for an additional 30 min, and then poured
into saturated aqueous NH4Cl (200 mL). The organic product
was extracted with hexanes (2 × 100 mL), dried over MgSO4,
filtered, concentrated, and purified by chromatography (SiO2,
2% EtOAc-hexanes) to give 15.0 g (64.7 mmol) of ketone 6
(2E,4E,6E)-7-(3,5-Di-ter t-b u t ylp h en yl)-3-m et h yloct a -
2,4,6-tr ien oic Acid (10a ). To 180 mg (0.49 mmol) of the
(2E,4E,6E)-ethyl ester 9a in 5 mL of MeOH was added 1 mL
of 5 N aqueous NaOH solution. The mixture was heated at
reflux for 10 min, cooled to room temperature, and acidified
with 20% aqueous HCl solution, and the organics were
extracted with ether (2 × 10 mL). The ether layer was washed
(H2O, brine), dried over MgSO4, filtered, and concentrated.
Purification by column chromatography (SiO2, 20% EtOAc-
hexanes) gave 157 mg (0.46 mmol) of the 2E,4E,6E isomer 10a
(93% yield): TLC (10% MeOH-90% CHCl3) Rf 0.6; mp 196-
1
(76% yield): TLC (5% EtOAc-95% hexanes) Rf 0.8; H-NMR
(CDCl3) δ 1.39 (s, 18H, 6(CH3)), 2.61 (s, 3H, CH3), 7.64 (t, J )
1 Hz, 1H, Ar-H), 7.80 (d, J ) 1 Hz, 2H, Ar-H).
3-(3,5-Di-ter t-bu tylph en yl)bu t-2-en en itr iles (7a an d 7b).
To 2.43 g (13.7 mmol) of diethyl cyanomethylphosphonate in
10 mL of dry THF was added 440 mg (10.96 mmol) of NaH.

Novel Retinoic Acid Receptor Agonists
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 14 2663
198 °C; 1H-NMR (CDCl3) δ 1.35 (s, 18H, 6(CH3)), 2.29, (s, 3H,
CH3), 2.41 (s, 3H, CH3), 5.84 (s, 1H, dCH), 6.41 (d, J ) 15 Hz,
1H, dCH), 6.54 (d, J ) 11 Hz, 1H, dCH), 7.08 (m, 1H, dCH),
7.32 (d, J ) 1 Hz, 2H, Ar-H), 7.39 (t, J ) 1 Hz, 1H, Ar-H);
HRMS found 340.2394, calcd 340.2402. Anal. (C23H32O2) C,
H.
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Suto, C. M.; Goldman, M. E.; Heyman, R. A. Synthesis and
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White, S. K.; Mais, D.E.; Berger, E.; Suto, C. M.; McClurg. M.
R.; Davies, P. J . A.; Heyman, R. A. Design of Novel RXR Selective
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update. Drug Saf. 1993, 9, 280-290.
(12) Yob, E. H.; Pochi, P. E. Side effects and long term toxicity of
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(13) David, M.; Hodak, E.; Lowe, N. J . Adverse effects of retinoids.
Med. Toxicol. Adverse Drug Exp. 1988, 3, 273-288.
(2E,4E,6Z)-7-(3,5-Di-ter t-b u t ylp h en yl)-3-m et h yloct a -
2,4,6-tr ien oic Acid (10b). The 2E,4E,6Z isomer 10b was
prepared in the same manner as 10a except that 9b was used
instead of 9a . Compound 10b was obtained in 70% yield: TLC
1
(10% MeOH-90% CHCl3) Rf 0.57; mp 221-222 °C; H-NMR
(CDCl3) δ 1.34 (s, 18H, 6(CH3)), 2.18, (s, 3H, CH3), 2.23 (s, 3H,
CH3), 5.77 (s, 1H, dCH), 6.25 (d, J ) 11 Hz, 1H, dCH), 6.29
(d, J ) 15 Hz, 1H, dCH), 6.84 (m, 1H, dCH), 7.10 (d, J ) 1
Hz, 2H, Ar-H), 7.37 (t, J ) 1 Hz, 1H, Ar-H); HRMS found
340.2425, calcd 340.2402. Anal. (C23H32O2) C, H.
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