Syntheses of 7-fluoro- and 6,7-difluoroserotonin and 7-fluoro- and 6,7-difluoromelatonin

Article abstract of DOI:10.1016/j.jfluchem.2006.06.015

The Abramovitch adaption of the Fischer indole synthesis gave low yields of 7-fluoro-5-methoxytryptamine due in part to decomposition during the required decarboxylation step. Therefore, 7-fluoro- and 6,7-difluoro-5-methoxytryptamines were prepared by rea

Full text of DOI:10.1016/j.jfluchem.2006.06.015

Journal of Fluorine Chemistry 127 (2006) 1256–1260
www.elsevier.com/locate/fluor
Short communication
Syntheses of 7-fluoro- and 6,7-difluoroserotonin
and 7-fluoro- and 6,7-difluoromelatonin
1
*
Jorge Heredia-Moya, Yoshio Hayakawa , Kenneth L. Kirk
Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health,
Department of Health and Human Services, Bethesda, MD 20892, United States
Received 1 June 2006; received in revised form 16 June 2006; accepted 17 June 2006
Available online 23 June 2006
Abstract
The Abramovitch adaption of the Fischer indole synthesis gave low yields of 7-fluoro-5-methoxytryptamine due in part to decomposition
during the required decarboxylation step. Therefore, 7-fluoro- and 6,7-difluoro-5-methoxytryptamines were prepared by reaction of aminobutyr-
aldehyde (generated in situ from the diethyl acetal) with 2-fluoro- and 2,3-difluoro-4-methoxyphenylhydrazine, and the products converted to the
corresponding serotonins. The melatonins were prepared by a one-pot reaction that involved in situ acetylation of the aminobutyraldehyde.
# 2006 Elsevier B.V. All rights reserved.
Keywords: Serotonin; Melatonin; Fischer indole synthesis
1. Introduction
In previous work we have prepared certain ring-fluorinated
analogues of both 1 and 2. For example, 6-fluoroserotonin (3),
4,6-difluoroserotonin (4), 6-fluoromelatonin (5), 4,6-difluor-
omelatonin (6) using the Abramovitch adaption of the Fischer
indole synthesis [8]. In addition, we prepared 4-fluoroserotonin
(7) and 4-fluoromelatonin (8) by regioselective electrophilic
fluorination of a 5-methoxygramine derivative, followed by
side-chain elaboration [9]. We also examined the effects of
fluorine substitution on such processes as serotonin transport
and storage [10–12]. The effects of fluorinated melatonins on
LHRF-stimulated release of lutinizing hormone were compared
to that of melatonin [13].
Serotonin (5-hydroxytryptamine, 5HT, 1) has many impor-
tant physiological actions in both the peripheral and central
nervous system (CNS). Included in peripheral responses are
actions on the cardiovascular [1], respiratory [2], and
gastrointestinal [3] systems mediated by stimulation or
inhibition of a wide variety of smooth muscles and nerves.
Serotonin also functions as a neurotransmitter in the central
nervous system (CNS) and plays an important role in
modulating mood, social behavior, appetite, sexual behavior
and pain [4]. Abnormalities in CNS serotonin function are
considered likely causes for certain mental illnesses.
Melatonin (N-acetyl-5-methoxytryptamine, 2), a neurohor-
mone primarily secreted at night by the pineal gland [5], is
derived from serotonin. Melatonin suppresses pituitary
response to lutinizing hormone releasing factor (LHRF). This
hormone is known to have a central role both in the regulation
of daily and seasonal rhythms [6] and in the modulation of other
endocrinological, neurophysiological, and behavioral functions
[7].
In this note, we report the synthesis of 7-fluoroserotonin (9a)
and 7-fluoromelatonin (10a), the last remaining benzene-ring
mono-fluorinated analogues of these important tryptamines.
We also report the synthesis of 4-7-difluoroserotonin (9b) and
6,7-difluoromelatonin (10b). We are currently examining the
effects of the ring-fluorinated serotonins on 5HT receptor
subtypes. These results will be reported elsewhere.
2. Results and discussion
Our initial synthetic strategy was analogous to the one we
used to prepare 6-fluoroserotonin, using 2-fluoro-4-methoxy
aniline (11a) as the starting point. In the synthesis of 3, the
key cyclization of the derived hydrazone occurred only in the
* Corresponding author.
E-mail address: kennethk@intra.niddk.nih.gov (K.L. Kirk).
1
Present address: National Institute of Advanced Industrial Science and
Technology (AIST Chubu), Nagoya 463-8560, Japan.
0022-1139/$ – see front matter # 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2006.06.015

J. Heredia-Moya et al. / Journal of Fluorine Chemistry 127 (2006) 1256–1260
1257
Scheme 1. (a) HCl, NaNO2, 0 8C, 1 h; (b) Na2CO3 (aq), 2-oxopiperidine-3-carboxylic acid, HOAc, 0 8C, pH 3.5, overnight; (c) ethylene glycol, MW, 230 8C, 10 min;
(d) EtOH, KOH, H2O, reflux, 24 h; (e) 0.5N HCl, MW, 160 8C, 20 min; (f) BBr3, À78 8C (1 h), rt (overnight); (g) Ac2O, rt, 1 h.
6-position ( para to the fluorine substituent), providing a
convenient route to 3 and 4. In the hydrazone 12, of the two
possible sites for new carbon–carbon bond formation during
cyclization, only the 6-position, meta to fluorine, is
unsubstituted. We thus expected a Fischer cyclization would
be an efficient route to the 7-fluoroindole system. Using 11a
in the Abramovich adaptation of the Fischer indole synthesis,
the hydrazone 12 was obtained in 58% yield (Scheme 1) [14].
To our surprise, Fischer cyclization of 12 under microwave
conditions in fact produced the desired fluorinated carboline
13, but this was accompanied by a comparable amount of non-
fluorinated carboline 14 [14]. Thus the cyclization also
occurred on the fluorine-substituted position, with loss of
fluorine. The acid-catalyzed cyclization also gave the mixture
of carbolines, but the total yield is lower compared with the
microwave assisted cyclization. We ascribe the lower yield
under acid conditions to competitive decomposition of the
tryptamine under the reaction conditions, a problem we
encountered in a subsequent step.
fluoromelatonin (10a) in good yield. Based on starting aniline
11a, the overall yield of serotonin derivative 9a was 1.2% and
the overall yield of melatonin 10a was 2.2%.
Due to the low yield obtained, an alternate synthetic route
was explored (Scheme 2) using the approach proposed by
Hwang and Lee [15] based on the use of 4-aminobutyraldehyde
diethyl acetal to construct the indolamine moiety. In situ
condensation of the released free aldehyde under acidic
conditions to form the hydrazone and Fischer cyclization
provide a convenient one-pot procedure for the critical indole
ring construction. Thus, reaction of 2-fluoro-4-methoxyphe-
nylhydrazine hydrochloride (17a), prepared from 11a in 58%
yield, with 4-aminobutyraldehyde diethyl acetal under acidic
condition produced 7-fluoro-5-methoxytryptamine (16a) in
31% yield (Scheme 2). Here again there was evidence for the
formation of the non-fluorinated indole that would be produced
by Fischer cyclization on the fluorine-bearing carbon.
Tryptamine 16a was converted to 7-fluoroserotonin (9a) as
described above. Using this approach, 7-fluoroserotonin (9a)
was synthesized in 7% overall yield from 11a, demonstrating
the higher efficiency of this route.
The amino acid 15 was obtained in good yield by ring
opening of the carboline 13 under strongly basic conditions.
However, the subsequent acid-catalyzed decarboxylation under
thermal or microwave conditions of 15, to afford the tryptamine
16a, proved problematic, and only a modest yields were
obtained. Acid-catalyzed decomposition appeared to be the
source of the low yield.
7-Fluoromelatonin (10a) was also prepared by a one-pot
reaction between the phenylhydrazine 17a, acetic anhydride
and 4-aminobutyraldehyde diethyl acetal in a mixed solvent
system of acetic acid/ethanol/water. In this reaction, acetylation
of the phenylhydrazine competes with the cyclization. 7-
Fluoromelatonin (10a) was obtained in 16% overall yield from
amine 11a.
Using the same synthetic route, 6,7-difluoroserotonin (9b)
and 6,7-difluoromelatonin (10b) were synthesized in 23% yield
and 53% yield, respectively, from 2,3-difluoro-4-methoxyani-
line (11b) through the phenylhydrazine 17b.
Tryptamine 16a was converted to 7-fluoroserotonin (9a) by
BBr3 mediated demethylation. Again, the yield was diminished
by accompanying decomposition in acid. Finally, as was the
case with previously synthesized fluoroserotonin derivatives,
the final product was purified as the creatinine sulfate salt.
Acylation of tryptamine 16a with acetic anhydride produced 7-

1258
J. Heredia-Moya et al. / Journal of Fluorine Chemistry 127 (2006) 1256–1260
Scheme 2. (a) HCl, NaNO2, 0 8C, 1 h; (b) SnCl, HCl, 0 8C, 4 h; (c) 5% HCl/EtOH (1/1), 4-aminobutyraldehyde diethyl acetal, 40 8C, overnight; (d) 4-
aminobutyraldehyde diethyl acetal, Ac2O, 0 8C, 1 h; (e) HOAc/EtOH/H2O (2.5/3.5/4), 40 8C, overnight; (f) BBr3, À78 8C (1 h), rt (overnight).
3. Conclusion
EtOAc in dichloromethane) to give 1.84 g (58%) of 12; mp 173–
1
175 8C (decomp); IR (KBr): 1658 cmÀ1; H NMR (300 MHz,
The Abramovitch adaptation of the Fischer indole synthesis
affords 7-fluoroserotonin and 7-fluoromelatonin in lower yields
than the synthesis from 4-aminobutyraldehyde diethyl acetal.
This latter approach decreases the number of reactions steps
and increases the total yield considerably. The presence of two
fluorine atoms in 6 and 7 positions on the benzene-ring confers
more stability than the mono fluoro-ring leading to an increase
in the overall yield of 9b and 10b.
acetone-d6) ppm: 1.96 (m, 2H), 2.66 (m, 2H), 3.38 (m, 2H), 3.76
(s, 3H), 6.73 (s, 1H), 6.76 (d, J = 5.9 Hz, 1H), 7.17 (broad s, 1H),
7.45 (t, J = 9.4Hz, 1H), 13.23(broad s, 1H); 19F NMR(282 MHz,
acetone-d6) d ppm: À57.71 (dd, J1 = 13.5 Hz, J2 = 9.6 Hz); MS
(CI) m/z: 252 [M + H]+, 269 [M + H + NH3]+.
4.3. 8-Fluoro-6-methoxy-1-oxo-1,2,3,4-terahydro-b-
carboline (13)
4. Experimental
A solution of 12 (1.0 g, 4.0 mmol) in ethylene glycol
(20 mL) was irradiated in a microwave oven for 10 min at
230 8C. Water was added, the mixture extracted with EtOAc
and the organic layer was dried over MgSO4. The solvent was
removed under vacuum and the residue was purified by column
chromatography (30% of acetone in dichloromethane) to afford
320.8 mg (34%) of 8-fluoro-6-methoxy-1-oxo-1,2,3,4-terahy-
dro-b-carboline (13) and 296.0 mg (32%) of 6-methoxy-1-oxo-
1-4-terahydro-b-carboline (14). Data for 13: mp 228–230 8C;
4.1. General
All the reagents were from Aldrich and used without further
purification. NMR spectra were run in CDCl3, acetone-d6,
DMSO-d6 or D2O on a Varian Gemini 300 MHz spectrometer.
Mass spectra were determined in Jeol SX-102 instrument. Infra
red spectra were recorded in BioRad Win FTIR instrument. The
microwave assisted reactions were run in a Biotage InitiatorTM
microwave oven.
1
IR (KBr): 1662 cmÀ1; H NMR (300 MHz, acetone-d6) ppm:
2.99 (dd, J1 = 7.0 Hz, J2 = 6.7 Hz, 2H), 3.66 (ddd, J1 = 7.0 Hz,
J2 = 6.7 Hz, J3 = 2.6 Hz, 2H), 3.84 (s, 3H), 6.74 (dd,
J1 = 12.5 Hz, J2 = 2.1 Hz, 1H), 6.79 (broad s, 1H), 6.94 (d,
J = 2.1 Hz, 1H), 10.90 (broad s, 1H); 19F NMR (282 MHz,
acetone-d6) d ppm: À54.96 (d, J = 12.6 Hz); MS (CI) m/z: 235
[M + H]+, 252 [M + H + NH3]+.
4.2. 2,3-Dioxopiperidine-3-(2-fluoro-4-
methoxy)phenylhydrazone (12)
To a vigorously stirred solution of 2-fluoro-4-methoxyaniline
(11a) (2.30 g, 21.3 mmol) in water (20 mL) and conc. HCl
(5.0 mL) at 0 8C was added a cooled solution of NaNO2 (1.35 g,
19.7 mmol) in water (4 mL). After a few minutes, the excess of
NaNO2 was decomposed with urea (0.81 g, 13.5 mmol) and the
mixture was neutralized with a cold solution (08 C) of 10%
Na2CO3 solution. The mixture was filtered into a cold stirred
solution of 2-oxopiperidine-3-carboxylic acid (previously pre-
pared from 2.4 g (14.2 mmol) of the ethyl ester by overnight
saponification with 30 mL of 0.5N NaOH at room temperature).
The reaction mixture was brought to pH 3.5 with acetic acid,
stirred at ice-water bath temperature for 5 h, and then kept in a
refrigerator overnight. The precipitated solid was filtered off,
washed with water and purified by column chromatography (5%
4.4. 7-Fluoro-5-methoxytryptamine-2-carboxylic acid (15)
A solution of KOH (697 mg) in water (3 mL) was added to a
solution of 13 (270 mg, 1.2 mmol) in ethanol (4 mL) and the
mixture was refluxed for 24 h. After evaporation of the ethanol,
the residue was diluted with water, chilled in ice, and
neutralized with HOAc. The precipitate was collected by
filtration and dried under reduced pressure to give 255.2 mg
(88%) of 15; mp 240–242 8C (decomp); IR (KBr): 1565 cmÀ1
;
1H NMR (300 MHz, DMSO-d6) ppm: 3.01 (m, 2H), 3.16 (m,
2H), 3.77 (s, 3H), 6.61 (dd, J1 = 12.5 Hz, J2 = 2.1 Hz, 1H), 6.89
(d, J = 2.0 Hz, 1H), 8.85 (s, 3H), 11.16 (broad s, 1H); 19F NMR

J. Heredia-Moya et al. / Journal of Fluorine Chemistry 127 (2006) 1256–1260
1259
(282 MHz, DMSO-d6) d ppm: À51.86 (d, J = 12.1 Hz); MS
(CI) m/z: 253 [M + H]+, 270 [M + H + NH3]+.
solution of SnCl2Á2H2O (5.5 g, 28.4 mmol) in conc. HCl
(10 mL) was added slowly to the solution of diazonium salt and
the mixture was stirred for 4 h. Water was added to the reaction
mixture and the insoluble hydrochloride was collected by
filtration to give 1.167 g (78%) of 17b; mp 180–195 8C
(decomp); 1H NMR (300 MHz, D2O) d ppm: 3.89 (s, 3H), 6.97
(m, 2H); 19F NMR (282 MHz, D2O) d ppm: À73.07 (dd,
J1 = 18.3 Hz, J2 = 9.0 Hz), À81.35 (dd, J1 = 18.3 Hz,
J2 = 9.0 Hz); MS (CI) m/z: 158.0 [M + H–NH3]+, 173.0
[M + H–H2]+, 175.0 [M + H]+, 176.0 [M + H–NH3 + H2O]+.
4.5. Decarboxylation of 15
A suspension of 15 (222 mg, 0.9 mmol) in 0.5N HCl (5 mL)
was irradiated under nitrogen in a microwave oven for 20 min at
160 8C. After the addition of 0.5N NaOH (5.0 mL), the product
was extracted with ethyl ether and the organic layer was dried
under Na2SO4. The solvent was removed under vacuum to give
32 mg of a mixture of 7-fluoro-5-methoxytryptamine (16a) and
7-fluoroserotonin (9a) (NMR spectroscopic ratio 1/0.07). The
mixture was used in the synthesis of 9a without purification (see
Section 4.12 below).
4.9. General procedure for the synthesis of 16a–b
To a solution of phenylhydrazine-hydrochloride 17a–b
(1.0 mmol) in 15 mL of 5% HCl/EtOH (1:1) was added 4-
aminobutyraldehyde diethyl acetal (1.0 mmol). The mixture of
reaction was stirred at 40 8C overnight or irradiated in a
microwave for 10 min at 100 8C. The reaction mixture was
concentrated in vacuum and the aqueous phase then made
alkaline with saturated Na2CO3 solution. The product was
extracted with ethyl ether until TLC indicated absence of
product in the extract (eluent: MeCN/EtOH/NH4OH (20/3/2)).
The organic layer was washed three times with water, three
times with brine and then dried over MgSO4. The solvent was
removed under vacuum and the residue was purified by column
chromatography (KP-Sil column, 1–10% of EtOH/NH4OH 3/2
in acetonitrile, UV 275–220 nm) to afford the tryptamines
(16a,b).
4.6. Acylation of 16a
To a vigorously stirred solution of 16a (24.5 mg, 0.12 mmol)
in EtOAc (2 mL) under nitrogen atmosphere was slowly added
dropwise acetic anhydride (0.36 mL, 0.15 mmol). The mixture
was stirred at room temperature by 1 h. The solvent was removed
under vacuum and the residue was purified by column
chromatography(KP-NHcolumn,20–100%ofEtOAcinhexane,
UV 245–275 nm) to produce 22.2 mg (75%) of 10a which was
recrystalized from toluene/hexane (see Section 4.16 below).
4.7. 2-Fluoro-4 methoxyphenylhydrazine hydrochloride
(17a)
To a vigorously stirred suspension of 11a (967 mg, 6.7 mmol)
in conc. HCl (10 mL) cooled to 0 8C was added a cold solution of
NaNO2 (574 mg, 8.1 mmol) in H2O (2 mL). The mixture was
stirred at 0 8C for 90 min. A cold solution of SnCl2Á2H2O (5.2 g,
26.9 mmol) in conc. HCl (10 mL) was then added slowly to the
solution of diazonium salt and the mixture was stirred for an
additional 4 h. After addition of water, the mixture was extracted
with ethyl ether. The aqueous phase was chilled in an ice bath,
made alkaline with a 20% NaOH solution and the product was
extracted with ethyl ether. The second ether extract was washed
with cold water and brine until neutral and then dried over
Na2SO4. The solution was concentrated in vacuum, cooled to
0 8C, and then saturated with dry hydrogen chloride. The pre-
cipitate that formed was collected by filtration to give 723.3 mg
(56%) of 17a; mp 151–155 8C (decomp); 1H NMR (300 MHz,
D2O) d ppm: 3.81 (s, 3H), 6.82 (ddd, J1 = 8.8 Hz, J2 = 2.7 Hz,
J3 = 1.2 Hz, 1H), 6.89 (dd, J1 = 12.7 Hz, J2 = 2.7 Hz, 1H), 7.24
(dd, J1 = 9.3 Hz, J2 = 8.8 Hz, 1H); 19F NMR (282 MHz, D2O) d
ppm: À47.36 (dd, J1 = 12.2 Hz, J2 = 9.2 Hz); MS (CI) m/z: 140
[M + H–NH3]+, 155 [M + H–H2]+, 157 [M + H]+.
4.10. 7-Fluoro-5-methoxytryptamine (16a)
Yield: 31%; mp 124–129 8C; 1H NMR (300 MHz, CDCl3) d
ppm: 2.86 (t, J = 6.7 Hz, 2H), 3.03 (t, J = 6.7 Hz, 2H), 3.84 (s,
3H), 6.62 (dd, J1 = 12.3 Hz, J2 = 2.0 Hz, 1H), 6.81 (d,
J = 2.1 Hz, 1H), 7.03 (broad s, 1H), 8.24 (broad s, 1H); 19F
NMR (282 MHz, CDCl3) d ppm: À57.84 (d, J = 12.1 Hz); MS
(CI) m/z: 192.0 [M + H–NH3]+, 209.0 [M + H]+, 250.0
[M + H + CH3CN]+.
4.11. 6,7-Difluoro-5-methoxytryptamine (16b)
Yield: 45%; mp 198–203 8C (decomp); 1H NMR (300 MHz,
CDCl3) d ppm: 1.29 (broad s, 2H), 2.85 (t, J = 6.7 Hz, 2H), 3.02
(t, J = 6.7 Hz, 2H), 3.94 (s, 3H), 6.85 (dd, J1 = 6.7 Hz,
J1 = 1.5 Hz, 1H), 7.04 (d, J = 2.0 Hz, 1H), 8.11 (broad s, 1H);
19F NMR (282 MHz, CDCl3) d ppm: À82.80 (d, J = 18.3 Hz),
À91.07 (dd, J1 = 18.3 Hz, J2 = 6.1 Hz); HRMS (EI) m/z—calcd.
for C11H13F2N2O: 227.0996; found: 227.1010.
4.12. General procedure for the synthesis of 9a–b
4.8. 2,3-Difluoro-4 methoxyphenylhydrazine hydrochloride
17b
To a vigorously stirred solution of fluoro-5-methoxytrypta-
mine 16a–b (0.16 mmol) in anhydrous CH2Cl2 (2 mL) cooled to
À78 8C and under nitrogen atmosphere was slowly added
dropwise 1 M solution of BBr3 in CH2Cl2 (0.5 mL, 0.5 mmol).
The mixture was allowed to warm to room temperature and
stirred overnight. After addition of water to the reaction mixture,
To a vigorously stirred suspension of 11b (1.1 g, 7.1 mmol)
in conc. HCl (10 mL) cooled to 0 8C was added a cooled
solution of NaNO2 (617 mg, 8.7 mmol) in H2O (2 mL). The
mixture was stirred at the same temperature for 90 min. A cold

1260
J. Heredia-Moya et al. / Journal of Fluorine Chemistry 127 (2006) 1256–1260
the dichloromethane layer was removed and the aqueous layer
was adjusted to pH 6 with 0.5N NaOH. The solvent was removed
under vacuum and the solid residue was extracted with hot 2-
propanol. The organic solution was concentrated under vacuum
and the mixture separated by column chromatography (KP-Sil
column, 1–10 % of EtOH/NH4OH 3/2 in acetonitrile, UV 220–
275 nm) to obtain the serotonin (free-amine). The serotonin (free
amine = 1 equiv.) was dissolved in hot 1/1 acetone–water (1 mL)
and a hot solution of 2 equiv. of creatinine hemisulfate in 1/1
acetone–water (1 mL) was added to the solution. Addition of
acetone (3 mL) and cooling gave 7-fluoroserotonin creatinine
sulfate monohydrate 9a–b.
275 nm) to produce the fluoromelatonins 10a–b which were
recrystalized from toluene/hexane.
4.16. 7-Fluoromelatonin (10a)
1
Yield: 27%; mp 114–116 8C; H NMR (300 MHz, CDCl3)
ppm: 1.94 (s, 3H), 2.92 (t, J = 6.7 Hz, 2H), 3.58 (dt,
J1 = 6.6 Hz, J2 = 6.3 Hz, 2H), 3.84 (s, 3H), 5.61 (broad s,
1H), 6.62 (dd, J1 = 12.3 Hz, J2 = 2.0 Hz, 1H), 6.81 (d,
J = 1.9 Hz, 1H), 7.03 (broad s, 1H), 8.34 (broad s, 1H); 19F
NMR (282 MHz, D2O) d ppm: À57.02 (d, J = 12.3 Hz); HRMS
(EI) m/z—calcd. for C13H15N2O2F: 250.1118; found:
250.1127; anal. calcd. for C13H15N2O2F: C 62.39%, H
6.04%, N 11.19%, F 7.59%; found: C 62.50%, H 6.04%, N
11.15%, F 7.42%.
4.13. 7-Fluoroserotonin (9a)
Yield: 40% as creatinine sulfate; mp > 200 8C (decomp); 1H
NMR (300 MHz, D2O) d ppm: 3.08 (t, J = 7.1 Hz, 2H), 3.11 (s,
3 H), 3.29 (t, J = 7.1 Hz, 2H), 4.24 (s, 2H), 6.66 (dd,
J1 = 12.2 Hz, J2 = 2.1 Hz, 1H), 6.88 (d, J = 2,1 Hz, 1H), 7.29 (s,
1H); 19F NMR (282 MHz, D2O) d ppm: À54.48 (d,
J = 12.2 Hz); MS (CI) m/z: 178.1 [M + H–NH3]+, 195.1
[M + H]+, 236.1 [M + H + CH3CN]+; anal. calcd. for
C14H22N5O7FS: C 39.71%, H 5.24%, N 16.54%; found: C
39.14%, H 5.05%, N 16.01%, F N/D.
4.17. 6,7-Difluoromelatonin (10b)
Yield: 68%; mp 153–154 8C; 1H NMR (300 MHz, CDCl3) d
ppm: 1.95 (s, 3H), 2.92 (t, J = 6.8 Hz, 2H), 3.57 (dt,
J1 = 6.7 Hz, J2 = 6.2 Hz, 2H), 3.94 (s, 3H), 5.53 (broad s,
1H), 6.87 (dd, J1 = 6.8 Hz, J2 = 1.1 Hz, 1H), 7.04 (d,
J = 2.2 Hz, 1H), 8.16 (broad s, 1H); 19F NMR (282 MHz,
CDCl3) d ppm: À82.55 (d, J1 = 18.3 Hz), À90.69 (dd,
J1 = 18.3 Hz, J2 = 6.1 Hz); HRMS (EI) m/z—calcd. for
C13H15F2N2O2: 269.1102; found: 269.1093; anal. calcd. for
C13H14N2O2F2: C 58.20%, H 5.26%, N 10.44%, F 14.16;
found: C 57.98%, H 5.24%, N 10.37%, F 14.11%.
4.14. 6,7-Difluoroserotonin (9b)
1
Yield: 65%; mp > 210 8C (decomp); H NMR (300 MHz,
D2O) d ppm: 2.21 (s, 2 H), 3.06 (t, J = 7.0 Hz, 2H), 3.10 (s, 3H),
3.27 (t, J2 = 7.0 Hz, 2H), 4.23 (s, 2H), 6.95 (d, J = 7.2 Hz, 1H),
7.26 (s, 1H); 19F NMR (282 MHz, D2O) d ppm: À80.52 (d,
J = 18.8 Hz), À90.56 (d, J = 18.8 Hz); MS (CI) m/z: 196.0
[M + H–NH3]+, 213.0 [M + H]+, 254.0 [M + H + CH3CN]+;
HRMS (EI)—calcd. for C10H11N2OF2: 213.0839; found:
213.0837; anal. calcd. for C14H21N5O7F2S: C 38.09%, H
4.80%, N 15.87%, F 8.61%; found: C 38.03%, H 4.62%, N
15.77%, F 8.34%.
Acknowledgement
This work was supported by the intramural research program
of NIDDK, NIH.
References
[1] W.H. Frishman, S. Huberfeld, S. Okin, Y.-H. Wang, A. Kumar, B. Shareef,
J. Clin. Pharmacol. 35 (1995) 541–572.
´
[2] R.M. Day, A.S. Agyeman, M.J. Segel, R.D. Chevere, J.M. Angelosanto,
Y.J. Suzuki, B.L. Fanburg, Biochem. Pharmacol. 71 (2006) 386–397.
[3] H.S. Ormsbee III, J.D. Fondacaro, Proc. Soc. Exp. Biol. Med. 178 (1985)
333–338.
4.15. General procedure for the synthesis of 10a–b
Acetic anhydride (0.1 mL, 1.05 mmol) was slowly added
with continuous stirring to 4-aminbutyraldehyde diethyl acetal
(0.19 mL, 0.96 mmol) under nitrogen atmosphere, at 5–10 8C.
The mixture was stirred at the same temperature for 1 h. The
cooling bath was removed and 5 mL of HOAc/EtOH/H2O
(2.5/3.5/4) was added. After 10 min, phenylhydrazine-hydro-
chloride 17a–b (0.95 mmol) and 5 mL of HOAc/EtOH/H2O
(2.5/3.5/4) were added and the reaction mixture was stirred at
40 8C overnight. The reaction mixture was then concentrated
at 40 8C in vacuum. Water (5 mL) and 5% HCl (5 mL) were
added and the product was extracted with EtOAc. The
combined extracts were washed with saturated NaHCO3
solution, brine, and dried over MgSO4. The solution was
filtered through a short silica gel bed and then concentrated in
vacuum. The residue was purified by column chromatography
(KP-NH column, 20–100% of EtOAc in hexane, UV 245–
[4] R.W. Fuller, Ann. Rev. Pharmacol. Toxicol. 20 (1980) 111–127.
[5] R.J. Reiter, Best Pract. Res. Clin. Endocrinol. Metab. 17 (2003) 273–285.
[6] P. Pevet, B. Bothorel, H. Slotten, M. Saboureau, Cell Tissue Res. 309
(2002) 183–191.
[7] (a) D.P. Cardinali, L.I. Brusco, S.P. Lloret, A.M. Furio, Neuroendocrinol.
Lett. 23 (2002) 9–13;
(b) N. Zisapel, CNS Drugs 15 (2001) 311–328;
(c) G.J.M. Maestroni, Expert Opin. Invest. Drug 10 (2001) 467–476.
[8] K.L. Kirk, J. Heterocyclic Chem. 13 (1976) 1253–1256.
[9] Y. Hayakawa, M. Singh, N. Shibata, Y. Takeuchi, K.L. Kirk, J. Fluorine
Chem. 99 (1999) 161–164.
[10] J.L. Costa, D.C. Joy, D.M. Maher, K.L. Kirk, S.N. Hui, Science 200 (1978)
537–539.
[11] J.L. Costa, K.L. Kirk, H. Stark, Br. J. Pharmacol. 75 (1982) 237–242.
[12] G. Rudnik, K.L. Kirk, H. Fishkes, S. Schuldiner, J. Biol. Chem. 264 (1989)
14865–14868.
[13] J.E. Martin, K.L. Kirk, D.C. Klein, Endocrinology 106 (1980) 398–401.
[14] R.A. Abramovitch, D. Shapiro, J. Chem. Soc. (1956) 4589–4592.
[15] K.-J. Hwang, T.-S. Lee, Synthetic Commun. 29 (1999) 2099–2104.