Use of dibutyl[14C]formamide as a formylating reagent in the Vilsmeier-Haack reaction and synthesis of a 14C-labeled novel phosphodiesterase-4 (PDE-4) inhibitor

Article abstract of DOI:10.1002/hlca.200590075

A simple, high-yielding synthesis of dibutyl[¹⁴C]formamide ([¹⁴C]DBF; 1) from ¹⁴CO₂ was developed (Scheme 1): reaction of LiBEt₃H and ¹⁴CO₂ followed by aqueous workup gave H¹⁴CO₂H in high yield. Conversion of the [¹⁴C]formic acid to 1 was effected by a standard carbodiimide coupling procedure. The utility of 1 as an alternative to dimethyl[ ¹⁴C]formamide ([¹⁴C]DMF) in alkylation reactions and in the [¹⁴C]Vilsmeier-Haack reaction was demonstrated for several substrates (Table 2). A ¹⁴C-labeled phosphodiesterase-4 (PDE-4) inhibitor, [¹⁴C]-2, was synthesized by application of this technology (Scheme 2).

Full text of DOI:10.1002/hlca.200590075

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Use of Dibutyl[14C]formamide as a Formylating Reagent in the
14
Vilsmeier± Haack Reaction and Synthesis of a C-Labeled Novel
Phosphodiesterase-4 (PDE-4) Inhibitor
by Jonathan Z. Ho*a), Charles S. Elmorea)1), Michael A. Wallacea), Dan Yaoa), Matthew P. Brauna),
Dennis C. Deana), David G. Melilloa), and Cheng-yi Chenb)
a) Department of Drug Metabolism
b) Department of Process Research, Merck Research Laboratories, RY80R-104, POBox 2000, Rahway,
New Jersey 07065, USA
(e-mail: jonathan_ho@merck.com)
A simple, high-yielding synthesis of dibutyl[14C]formamide ([14C]DBF; 1) from 14CO2 was developed
(Scheme 1): reaction of LiBEt3H and 14CO2 followed by aqueous workup gave H14CO2H in high yield.
Conversion of the [14C]formic acid to 1 was effected by a standard carbodiimide coupling procedure. The utility
of 1 as an alternative to dimethyl[14C]formamide ([14C]DMF) in alkylation reactions and in the [14C]Vilsmeier ±
Haack reaction was demonstrated for several substrates (Table 2). A 14C-labeled phosphodiesterase-4 (PDE-4)
inhibitor, [14C]-2, was synthesized by application of this technology (Scheme 2).
Introduction. ± Dimethylformamide (DMF) is a reagent of great utility in organic
synthesis and is often utilized as an electrophile in alkylations or Vilsmeier ± Haack
reactions to synthesize aldehydes (for recent reviews, see [1]). Its role as a C1-synthon
makes dimethyl[14C]formamide ([14C]DMF) a useful radiolabeling reagent, but due to
the high cost of commercial [14C]DMF and the cumbersome purifications described in
literature preparations [2], it has been infrequently used in radiolabeled syntheses. The
synthesis of a more lipophilic [14C]DMF equivalent might allow for simplified handling
as extractions with H2Owould not be precluded. Furthermore, there is ample literature
precedent for expecting a DMF equivalent such as dibutyl[14C]formamide ([14C]DBF;
1) to react similarly to DMF in Vilsmeier ± Haack reactions and alkylations [1]. Based
on this analogy, we developed a short, high-yielding synthesis of [14C]DBF as an
alternative to [14C]DMF. We have also demonstrated the utility of this reagent in the
radiochemical synthesis of a novel 14C-labeled phosphodiesterase-4 (PDE-4) tracer,
[14C]-2.
Results and Discussion. ± 1. Dibutyl[14C]formamide ([14C]DBF; 1). The reported
syntheses of [14C]DMF entail the high-temperature reaction of dimethylamine and
[14C]formic acid [2a] or activation of the [14C]formic acid as a mixed anhydride and
subsequent reaction with Me2NH [2b]. In these preparations, the purification of the
product is achieved by distillation [2c]. While these are viable, high-yielding synthetic
procedures for large-scale preparation, they are inefficient on a small scale. We
therefore investigated a standard amide-bond-forming reaction to couple the dialkyl-
1
)
Current address: CNS Chemistry, AstraZeneca, Wilmington, DE 19850.
ꢀ 2005 Verlag Helvetica Chimica Acta AG, Zürich

Helvetica Chimica Acta ± Vol. 88 (2005)
1041
amine and [14C]formic acid with the expectation that a standard extractive workup
would remove the bulk of the impurities leaving the dialkyl[14C]formamide in the
organic layer2).
Reaction of 14CO2 with LiBEt3H in THF gave [14C]formic acid in 80% isolated yield
after acidification with aqueous HCl solution followed by extraction with CH2Cl2
(Scheme 1). Coupling of the acid with dibutylamine in presence of 1-[3-(dimethyl-
amino)propyl]-3-ethylcarbodiimide hydrochloride (EDC) or 2-(1H-benzotriazol-1-
yl)-1,1,3,3-tetramethyluronium tetrafluoroborate (TBTU) gave dibutyl[14C]formamide
(1) in 90% yield and high radiochemical purity (95 ± 99%) after flash chromatography
(silica gel). The compound was stable to long term storage in CH2Cl2, toluene, and
MeOH3).
Scheme 1. Conversion of 14CO2 to Bu2N14CHO
The alkylation of dibutyl[14C]formamide (1) with several different nucleophiles was
studied (Table 1). The reactions were conducted with 1 equiv. of 1 and 1 ± 2 equiv. of
alkylating reagent at À 788. Yields were typically high and resulted in no major
radiochemical by-products.
The utility of dibutyl[14C]formamide (1) as a substrate in the Vilsmeier ± Haack
reaction was also probed. Formamide 1 was treated with either phosphorous
oxychloride (ˆ phosphoric trichloride) or diphosphoryl chloride [4] to give a
Vilsmeier ± Haack reagent which was coupled with a variety of aromatic substrates.
The yields for the coupling correlate with the electronic nature of the arene, with only
activated aromatic substrates producing good yields (Table 2). This is consistent with
the general trend of the Vilsmeier ± Haack reactions, i.e., the higher the electron density
of the substrate, the better the yields for the product. As reported previously by Heaney
and co-workers [4], the use of diphosphoryl chloride gave higher and more
reproducible yields than POCl3, which is at least partially due to the added stability
of the Vilsmeier ± Haack reagent formed from Cl2PO2POCl2 over the adduct with
POCl3.
2. 14C-LabeledPhosphodiesterase-4 (PDE-4) Inhibitor via [14C]DBF. In an effort to
develop new therapeutic agents for the treatment of asthma, Merck has been engaged
in the study of phosphodiesterase-4 (PDE-4) inhibitors. PDE-4 is a high-affinity
cAMP-selective isozyme, and is found in almost all cell types that have been implicated
in asthma pathogenesis [5]. Candidate 2 was identified as a potent, selective PDE-4
inhibitor [6]. To perform preliminary drug metabolism and distribution studies, a 14C-
labeled tracer was required.
If the target of synthesis was dibutyl[14C]formamide rather than [14C]DMF, an extractive workup would
also be possible for this synthetic approach potentially eliminating the need for the distillation. For a
preliminary communation on dibutyl[14C]formamide, see [3]. Portions of this work were presented at the
2004 Fall meeting of the USA Northeast Chapter International Isotope Society, King of Prussia,
Pennsylvania, USA, October 28 ± 29, 2004.
2
)
)
Dibutyl[14C]formamide was stored at À 308 with no change in the HPLC trace over a 3-month period.
3

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Table 1. Synthesis of 14C-LabeledAldehydes via Alkylation of Bu2N14CHO
Substrate
PhMgBr
Product
Yielda)
75%
Ph14CHO60%
60%
60%
a) Isolated radiochemical yield based on Bu2N14CHO.
Friesen and co-workers have reported the synthesis of 2 from DMF [7]. We
reasoned that replacement of DMF with [14C]DBF would allow preparation of 14C-
labeled 2 via the same route (Scheme 2). Vilsmeier ± Haack reaction of 1 with the
dianion generated from 3 gave a 14C-labeled hydroxybenzaldehyde 4 in 78% yield.
Alkylation of 4 with sodium chlorodifluoroacetate in the presence of K2CO3 was
readily accomplished. Reaction of 5 with the anion generated from thiazole 6 led to a
racemic mixture of alcohol 7 in 87% yield. We could convert racemic 7 to 10, but we felt
that we would obtain a better yield of the desired (S)-isomer 10 by conducting
oxidation of 7 to the corresponding ketone followed by asymmetric reduction as
described by Frey and co-workers [7d]. Oxidation of 7 to 8 with MnO2 was achieved in
85% yield. Asymmetric reduction of 8 with freshly prepared (‡)-(R)-BINAL
(ˆ lithium {(R)-[1,1'-binaphthalene]-2,2'-diolato}ethoxyhydroaluminate) resulted in

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Table 2. Synthesis of 14C-Labeled Aldehydes via Vilsmeier± Haack Reaction
Substrate
Product
Catalyst
POCl3
Yielda)
80%
POCl3
48%
Cl2PO2POCl2
Cl2PO2POCl2
78%
82%
Cl2PO2POCl2
Cl2PO2POCl2
74%
83% (85 : 15)
a) Isolated radiochemical yield based on Bu2N14CHO.
enantiomerically enriched 9 (enantiomer ratio (R)/(S) 85 :15). This enantiomer ratio
was kept unchanged throughout the subsequent reactions. Tosylation of 9 followed by
displacement with ethyl pyridine-3-acetate 1-oxide gave 10, in which the chiral center
was inverted. Removal of the methoxymethyl (MOM) protecting group in 10 yielded
11, and hydrolysis of the ethyl ester in 11 tandem with decarboxylation provided [14C]-2.
Purification of the final tracer was effected by prep. reversed-phase HPLC followed by
a prep. chiral LC separation to furnish [14C]-2 (1.6 mCi) with 99.6% radiochemical
purity and 99.5% ee.
Conclusion. ± We developed a simple and convenient synthesis of dibutyl[14C]form-
amide (1) from 14CO2 and showed that 1 is a good replacement for [14C]DMF as a
formylating reagent in 14C-label synthesis. The utility of 1 was demonstrated in the
preparation of a novel 14C-labeled PDE-4-inhibitor tracer.

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Scheme 2. Synthesis of [14C]-2
a) 1. BuLi (1.0 equiv.), THF, À 408, 0.5 h; 2. s-BuLi (1.2 equiv.), THF, N,N,N',N'-tetramethylethane-1,2-diamine
(TMEDA), À 308, 0.5 h; 3. 1, POCl3, THF, 08, 1 h; 78%. b) ClF2CCO2Na, K2CO3, DMF, H2O, 1008, 2 h; 95%.
c) BuLi, tBuOMe, À 408, 1 h. d) 5, tBuOMe, À 408 to À 108, 1 h; 87% for 2 steps. e) MnO2, tBuOMe, 608, 2 h;
85%. f) (‡)-(R)-BINAL, THF, TMEDA, À 508, 1 h; 65%. g) 1. BuLi, Ph3CH, THF, À 788, 10 min; 2. Ts2O,
THF, À 788, 0.5 h; 3. ethyl pyridine-3-acetate 1-oxide, lithium hexamethyldisilazanide (LiHMDS), THF,
3,4,5,6-tetrahydro-1,3-dimethylpyrimidin-2(1H)-one (DMPU), À 358, 1 h; then this enolate was added to the
tosylate soln. at À 788, and stirred at À 788 for 20 h. h) Conc. HCl soln., MeOH, 608, 2 h. i) LiOH, H2O, r.t.,
1.5 h. j) PhCl, 1358, 8 h; 40% for 3 steps.

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Experimental Part
General. Anh. solvents were obtained from Aldrich and were dried over 4-Š molecular sieves for at least
24 h prior to use. FC ˆ flash chromatography. Anal. HPLC: Shimadzu HPLC system with LC-10ATVP pumps,
SPD-10AVP UV detector, CTO-10ASVP column oven heated to 408, a SCL-10A controller, and a Packard-
RadiomaticTM-150TR flow monitor; product identification by HPLC comparison with unlabeled material by
using either MethodA (40 ! 80% MeCN/0.1% aq. CF3COOH soln. over 30 min), MethodB (10 ! 60%
MeCN/0.1% aq. CF3COOH soln. over 30 min), or MethodC (40 ! 100% MeCN/0.1% aq. CF3COOH soln.
over 30 min), all reversed-phase analyses were conducted on a Zorbax-SB-C-8 column heated to 408 and were
concluded with a 10 min wash with 100% MeCN; the chiral assay was performed by using MethodD
(ChiralPak-AD column (4.6 Â 250 mm), flow rate 1.0 ml/min, 2% EtOH/hexane). 1H-NMR Spectra: Varian-U-
400 spectrometer.
[14C]Formic Acid. A flask containing 1m LiBEt3H (7 ml) in THF (7 mmol) was cooled in liq. N2 and
evacuated to 0.01 Torr. Then 14CO2 (250 mCi, 53 mCi/mmol, 4.72 mmol; NEN) was transferred via standard
vacuum techniques. The mixture was warmed to r.t. and stirred for 3 h. The flask was purged with N2 for 10 min,
and then 6m HCl (2 ml) was added which resulted in extensive bubbling. The THF was removed by passing a N2
stream over the soln., and the aq. soln. was extracted with Et2O(5 Â 20 ml). The Et2Osoln. was dried (MgSO 4)
to give 204 mCi (82%) of [14C]formic acid.
Dibutyl[14C]formamide (1; [14C]DBF): Procedure A with EDC as the Coupling Agent. A soln. of
[14C]formic acid (106 mCi, 2.0 mmol, 53 mCi/mmol) in Et2Owas concentrated to near dryness under a stream of
N2, and the residual Et2Owas removed by chasing with CH 2Cl2 (2 Â 10 ml). To the oil was added CH2Cl2 (5 ml),
N,N-dimethylpyridin-4-amine (DMAP; 228 mg, 1.87 mmol), and Et3N (526 mg, 5.2 mmol). The resulting
mixture was stirred for 1 h. A soln. of EDC (1.4 g, 7.30 mmol) and 1-hydroxy-1H-benzotriazole (HOBt; 1.3 g,
7.3 mmol) in CH2Cl2 (5 ml) was added, followed by addition of Bu2NH (0.5 ml). The soln. was stirred for 12 h at
r.t. The reaction was halted by addition of sat. NaHCO3 soln. (5 ml). The org. layer was washed with 1m HCl
(3 Â 5 ml), NaHCO3 soln. (5 ml), and sat. NaCl soln. (5 ml). The org. layer was counted at 92 mCi (90%), and
the radiochemical purity was assessed by HPLC (MethodA ) at 95%.
[14C]DBF (1): Procedure B with TBTU as the Coupling Agent. A soln. of 100 mCi of [14C]formic acid
(2.0 mmol, 56 mCi/mmol) in Et2Owas concentrated to near dryness under a stream of N 2, and the residual Et2O
was removed by chasing with CH2Cl2 (2 Â 10 ml). To the oil was added CH2Cl2 (5 ml), DMAP (228 mg,
1.87 mmol), and Et3N (526 mg, 5.2 mmol). The resulting mixture was stirred for 1 h. A soln. of 2-(1H-
benzotriazol-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate (TBTU; 1.5 g, 7.30 mmol) in CH2Cl2 (5 ml)
was added, followed by addition of Bu2NH (0.5 ml). The soln. was stirred for 1 h at r.t., and then worked up as
described in Procedure A. The org. layer was counted at 95 mCi (95%), and the radiochemical purity was
assessed by HPLC (MethodA ) at 99%.
General Procedure for the Vilsmeier± Haack Reaction: 1-Methyl-1H-indole-3-[14C]carboxaldehyde. A soln.
of 1 (18 mCi, 0.34 mmol, 53 mCi/mmol) in toluene (1 ml) was stirred as diphosphoryl chloride (75 ml,
0.54 mmol) was added, and the resulting soln. was stirred for 30 min. A soln. of 1-methyl-1H-indole (52 mg,
0.40 mmol) in toluene (0.1 ml) was added, and the resulting soln. was stirred for 3 h after which HPLC
(MethodA ) indicated the reaction to be complete; therefore, aq. NaOH soln. (2 ml) was added, and the
biphasic soln. was stirred for 2 h. The aq. soln. was extracted with AcOEt (3 Â 3 ml). The combined org. phase
counted at 18 mCi (88% radiochemical purity by HPLC (MethodA ). Purification by FC (silica gel, 2% MeOH/
CH2Cl2) gave 14 mCi (78%) of 1-methyl-1H-indole-3-[14C]carboxaldehyde. The compound was characterized
by HPLC (MethodB ).
General Procedure for Alkylation of Dibutyl[14C]formamide (1) with (4-Isopropylphenyl)lithium: 4-
Isopropyl[14C]benzaldehyde. A soln. of 1-iodo-4-isopropylbenzene (840 ml, 4.8 mmol) in THF (3.4 ml) at À 788
was stirred as 2.5m BuLi (2.9 ml, 7.2 mmol) was added via syringe over 5 min. After stirring for 40 min, a soln. of
1 (140 mCi 58 mCi/mmol, 2.4 mmol) in toluene (6 ml) was added, and the mixture was stirred for 1 h after which
HPLC (MethodC ) showed no remaining 1; therefore, H2O(10 ml) was added. The soln. was extracted with
Et2O(30 ml) and the org. layer concentrated to ca. 3 ml. Purification by FC (silica gel, 8% Et2O/hexane) gave 4-
isopropylbenz[14C]aldehyde (105 mCi, 75%); 99.7% radiochemical purity by HPLC (MethodC ).
3-(Cyclopropyloxy)-4-hydroxybenz[14C]aldehyde (4). A soln. of 4-bromo-(2-cyclopropyloxy)phenol [7]
(458 mg, 2.0 mmol) in THF (10 ml) under N2 was cooled to À 788 with stirring, and 1.4m MeLi in Et2O(1.4 ml,
2.0 mmol) was added at such a rate that the internal temp. did not exceed À 308. The mixture was then stirred at
À 408 for 0.5 h, cooled to À 788, and charged with 1.3m s-BuLi in cyclohexane (2 ml, 2.6 mmol) at À 788. After
0.5 h, a soln. of freshly prepared 1 (78 mCi) and diphosphoryl chloride (75 ml, 0.54 mmol) in THF (3 ml) and

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cyclohexane (1 ml) was added, and the resulting mixture was warmed to 08. After 1 h, toluene (10 ml) and 2m aq.
HCl (10 ml) were added. The aq. layer was extracted with toluene (5 ml  2), the combined org. layer
evaporated, and the residue purified by FC (silica gel, hexane/AcOEt 70 :30): 4 (62 mCi, 79%; 53 mCi/mmol);
radiochemical purity 99% (MethodB ). 1H-NMR (CDCl3): 0.85 (m, 2H); 0.90 (m, 2 H); 3.90 (m, 1 H); 6.03
(s, 1 H); 7.04 (d, J ˆ 8.1, 1 H); 7.45 (dd, J ˆ 1.9, 8.1, 1 H); 7.73 (d, J ˆ 1.9, 1 H); 9.85 (s, 1 H). MS: 181.2 ([M ‡
‡
H] ).
3-(Cyclopropyloxy)-4-(difluoromethoxy)benz[14C]aldehyde (5). Under N2, sodium chlorodifluoroacetate
(213 mg, 1.4 mmol), K2CO3 (290 mg, 2.1 mmol), and 1 (20 mCi 53 mCi/mmol) in DMF (1.5 ml) and H2O
(0.2 ml) were mixed under stirring, degassed with N2 for 5 min, and then stirred at 1008 for 2 h. After cooling to
r.t., the mixture was purified by FC (silica gel, CH2Cl2): 5 (19 mCi, 95%; 53 mCi/mmol); radiochemical purity
98% (MethodB ). 1H-NMR (CDCl3): 0.77 (m, 2 H); 0.82 (m, 2 H); 3.81 (m, 1 H); 6.59 (t, J ˆ 7.2, 1 H); 7.22
‡
(d, J ˆ 8.2, 1 H); 7.41 (dd, J ˆ 1.9, 8.2, 1 H); 7.77 (d, J ˆ 1.9, 1 H); 9.88 (s, 1 H). MS: 230.2 ([M ‡ H] ).
(aRS)-a-[3-(Cyclopropyloxy)-4-(difluoromethoxy)phenyl]-2-[2,2,2-trifluoro-1-(methoxymethoxy)-1-(tri-
fluoromethyl)ethyl]thiazol-5-[14C]methanol (7). Under N2, a soln. of 2-[2,2,2-trifluoro-1-(methoxymethoxy)-1-
(trifluoromethyl)ethyl]thiazole [7] (6; 550 mg, 18.6 mmol), tBuOMe (60 ml), and toluene (10 ml) was cooled to
À 788, and 1.6m BuLi in hexane (12 ml, 19 mmol) was added. The mixture was stirred at À 408 for 1 h, then a
soln. of 5 in toluene (2 ml) was introduced. After stirring at À 408 for an additional hour, the mixture was
warmed to À 108. Brine (5 ml) was added; the mixture was concentrated and purified by FC (silica gel, hexane/
AcOEt 70 :30): 7 (61 mCi, 89%; 53 mCi/mmol); radiochemical purity 96% (MethodB ). 1H-NMR (CDCl3): 0.80
(m, 2 H); 0.81 (m, 2 H); 3.52 (s, 3 H); 3.79 (m, 1 H); 5.06 (s, 2 H); 6.09 (s, 1 H); 6.52 (t, J ˆ 7.9, 1 H); 7.00
‡
(dd, J ˆ 1.9, 8.3, 1 H); 7.17 (d, J ˆ 8.3, 1 H); 7.40 (d, J ˆ 1.9, 1 H); 7.68 (s, 1 H). MS: 526.1 ([M ‡ H] ).
[3-(Cyclopropyloxy)-4-(difluoromethoxy)phenyl)]{2-[2,2,2-trifluoro-1-(methoxymethoxy)-1-(trifluoro-
methyl)ethyl]thiazol-5-yl}[14C]methanone (8). Under N2, MnO2 (162 mg, 1.9 mmol) and 7 (20 mCi, 0.38 mmol;
53 mCi/mmol) in tBuOMe (10 ml) were stirred at 608 for 2 h. After cooling to r.t., the mixture was purified by
FC (silica gel, hexane/AcOEt 70 :30): 8 (17 mCi, 85%; 53 mCi/mmol); radiochemical purity 94% (MethodC ).
1H-NMR (CDCl3): 0.88 (m, 2 H); 0.90 (m, 2 H); 3.59 (s, 3 H); 3.90 (m, 1 H); 5.17 (s, 2 H); 6.65 (t, J ˆ 7.1, 1 H ) ;
‡
7.30 (d, J ˆ 8.2, 1 H); 7.54 (dd, J ˆ 2.1, 8.2, 1 H); 7.87 (d, J ˆ 2.1, 1 H); 8.36 (s, 1 H). MS: 524.2 ([M ‡ H] ).
(aR)-a-[3-(Cyclopropyloxy)-4-(difluoromethoxy)phenyl]-2-[2,2,2-trifluoro-1-(methoxymethoxy)-1-(tri-
fluoromethyl)ethyl]thiazol-5-[14C]methanol (9). Under N2, 5.68m EtOH in THF (0.50 ml in 1.62 ml) was added
dropwise within 15 min to 1.0m LiAlH4 in THF (8.2 g). Then, a soln. of (‡)-(R)-[1,1'-binaphthalene]-2,2'-diol
(ˆ(‡)-(R)-Binol) in THF (2.63 g in 7.3 ml) was added within 40 min. Over the time, the suspension turned into
a soln., and the final temp. was kept at 608. Caution: on addition of (‡)-(R)-Binol, an exothermic reaction takes
place. After stirring at 608 for 0.5 h, neat TMEDA (1.39 ml) was added quickly to the slurry. The mixture was
stirred for 15 min at 608 before it was allowed to cool to r.t. This slurry of (‡)-(R)-BINAL was stirred under a
positive N2 pressure, and was cooled to À 788. Ketone 7 (17 mCi, 0.3 mmol) in THF (4 ml) was then added via a
syringe and a needle. The mixture was stirred at À 508 for 1 h and then quenched with sat. NH4Cl soln. (4 ml) at
À 508. The mixture was filtered through a pad of Celite and purified by FC (silica gel, hexane/AcOEt 70 :30): 9
(11 mCi, 65%; 53 mCi/mmol); radiochemical purity 99% (MethodC ); ratio (R)/(S) 85 :15 (MethodD ).
1H-NMR (CDCl3): 0.80 (m, 2 H); 0.81 (m, 2 H); 3.52 (s, 3 H); 3.79 (m, 1 H); 5.06 (s, 2 H); 6.09 (s, 1 H); 6.52
(t, J ˆ 7.9, 1 H); 7.00 (dd, J ˆ 1.9, 8.3, 1 H); 7.17 (d, J ˆ 8.3, 1 H); 7.40 (d, J ˆ 1.9, 1 H); 7.68 (s, 1 H). MS: 526.1
‡
([M ‡ H] ).
a-{(1S)-[3-(Cyclopropyloxy)-4-(difluoromethoxy)phenyl]{2-[2,2,2-trifluoro-1-(methoxymethoxy)-1-(tri-
fluoromethyl)ethyl]thiazol-5-yl}[14C]methyl}pyridine-3-acetic Acid Ethyl Ester 1-Oxide (10). At À 788, 1.0m
LiHMDS in THF (1.8 ml, 1.8 mmol) was added to a soln. of ethyl pyridine-3-acetate 1-oxide (364 mg, 2 mmol)
in THF (2.5 ml) and DMPU (1 ml) at À 788. The mixture was then stirred at À 358 for 1 h to form a lithium
enolate slurry. In a separated flask, 9 (10 mCi, 0.17 mmol) in THF (3 ml) was stirred at À 788, while a drop of
1% Ph3CH soln. in THF was added followed by 1.6m BuLi in hexane (0.2 ml, 0.32 mmol). After stirring at À 788
for 10 min, a soln. of Ts2O(130 mg, 0.4 mmol) in THF (1 ml) was introduced. After stirring at À 788 for 0.5 h,
the previously prepared lithium enolate slurry was transferred via cannula to the cold (À 788) tosylate soln. The
resulting soln. was kept in a À 788 freezer for 20 h. Then 1m aq. HCl was injected into the cold (À 788) mixture
t
t
followed by BuOMe. The final pH was ca. 6. The aq. layer was extracted with BuOMe (5 Â 10 ml), the
combined org. layer evaporated, and the residue purified by FC (silica gel, MeOH/AcOEt 10 :90): 10 (4.4 mCi,
44%; 53 mCi/mmol); radiochemical purity 97% (MethodC ). 1H-NMR (CDCl3): 0.78 (m, 1 H); 0.84 (m, 1 H);
0.99 (t, J ˆ 7.1, 3 H); 3.50 (s, 3 H); 3.82 (m, 1 H); 4.15 (d, J ˆ 12.0, 1 H); 4.90 (d, J ˆ 12.0, 1 H); 5.03 (s, 2 H); 6.41
(t, J ˆ 7.6, 1 H); 6.69 (dd, J ˆ 2.0, 8.1, 1 H); 6.98 (d, J ˆ 8.3, 1 H); 7.01 (d, J ˆ 2.4, 1 H); 7.16 (d, J ˆ 8.0, 1 H); 8.04
‡
(m, 1 H); 8.11 (m, 1 H); 8.23 (s, 1 H). MS: 181.2 ([M ‡ H] ).

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5-{(1S)-1-[3-(Cyclopropyloxy)-4-(difluoromethoxy)phenyl]-2-(1-oxidopyridin-3-yl)[1-14C]ethyl}-a,a-bis-
(trifluoromethyl)thiazol-2-methanol ([14C]-2). A soln. of MOM ester 11 (4 mCi, 0.075 mmol) in MeOH (2 ml)
and 36% HCl soln. (0.1 ml, 1 mmol) was stirred at 608 for 2 h. After cooling to r.t., a soln. of LiOH (100 mg,
2.4 mmol) in H2O(0.5 ml) was introduced, and the soln. was stirred at r.t. for 1.5 h. Aq. 2.0 m HCl was used to
adjust the pH to 2, and the mixture was evaporated. Chlorobenzene (2 ml) was added and the soln. was stirred at
1358 for 8 h. The mixture was purified by reversed-phase HPLC (Zorbax-RX-C-18 prep. column 25 Â 250,
MeCN/H2O/CF3COOH 35 :65 :0.1) and chiral LC separation (ChiralPak-AD semi-prep. column 25 Â 250,
EtOH/hexane 2 :98): [14C]-2 (1.6 mCi, 40%; 53 mCi/mmol); 99.6% radiochemical purity (MethodC ) and 99.5%
1
ee (MethodD ). H-NMR (CDCl3): 0.66 (m, 1 H); 0.76 (m, 2 H); 0.79 (m, 2 H); 3.30 (m, 1 H); 3.44 (m, 1 H);
3.67 (m, 1 H); 4.45 (t, J ˆ 7.8, 1 H); 6.49 (t, J ˆ 7.7, 1 H); 6.78 (dd, J ˆ 2.1, 8.2, 1 H); 6.91 (d, J ˆ 7.8, 1 H); 7.05
(d, J ˆ 2.1, 1 H); 7.11 (d, J ˆ 8.2, 1 H); 7.17 (t, J ˆ 7.8, 1 H); 7.65 (s, 1 H); 8.11 (d, J ˆ 7.5, 1 H); 8.12 (s, 1 H). MS:
‡
573.1 ([M ‡ H] ).
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ReceivedJanuary 6, 2005