The formation of 2-hydroxy-4-hydroxymethyl-3-(indol-3-yl)cyclopent-2-enone derivatives from ascorbigens

Article abstract of DOI:10.1016/S0008-6215(00)00310-4

A facile preparation is described of 3-(indol-3-yl)-2-hydroxy-4-hydroxymethylcyclopent-2-enone and its N-derivatives in 15-40% yields by the degradation of ascorbigen or its N-derivatives in a warm solution of L-ascorbic acid through a sequential domino reaction. The same cyclopentenone derivatives were obtained in 30-40% yields by the condensation of (N-alkylindol-3-yl)glycolic acids with ascorbic acid. 2,6-Dihydroxy-1-(indol-3-yl)hexa-1,4-diene-3-one and 2-hydroxy-4-hydroxymethyl-5-(indol-3-yl)cyclopent-2-enone were identified as intermediates in this reaction.

Full text of DOI:10.1016/S0008-6215(00)00310-4

www.elsevier.nl/locate/carres
Carbohydrate Research 330 (2001) 469–477
The formation of
2-hydroxy-4-hydroxymethyl-3-(indol-3-yl)-
cyclopent-2-enone derivatives from ascorbigens
Alexander M. Korolev, Larisa N. Yudina, Ilyia I. Rozhkov, Ludmila N. Lysenkova,
Eduard I. Lazhko, Yury N. Luzikov, Maria N. Preobrazhenskaya*
Gause Institute of New Antibiotics, Russian Academy of Medical Sciences, B. Pirogo6skaya 11,
Moscow 119867, Russia
Received 3 July 2000; accepted 15 November 2000
Abstract
A facile preparation is described of 3-(indol-3-yl)-2-hydroxy-4-hydroxymethylcyclopent-2-enone and its N-deriva-
tives in 15–40% yields by the degradation of ascorbigen or its N-derivatives in a warm solution of L-ascorbic acid
through a sequential domino reaction. The same cyclopentenone derivatives were obtained in 30–40% yields by the
condensation of (N-alkylindol-3-yl)glycolic acids with ascorbic acid. 2,6-Dihydroxy-1-(indol-3-yl)hexa-1,4-diene-3-
one and 2-hydroxy-4-hydroxymethyl-5-(indol-3-yl)cyclopent-2-enone were identified as intermediates in this reaction.
© 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Ascorbigen;
L
-Ascorbic acid; 2-Hydroxy-4-hydroxymethyl-3-(indol-3-yl)cyclopent-2-enone
1. Introduction
labile compound which undergoes various
transformations under mild (even in biological
nonenzymatic) conditions. Investigations of
the products of ascorbigen transformations is
thus important for understanding its biologi-
cal properties.
Ascorbigen,
xylo-hex-3-ulofuranosono-1,4-lactone
can be readily obtained by the interaction of
3-hydroxymethylindole and -ascorbic acid.
This reaction represents a rare example of
C-alkylation of -ascorbic acid under mild
2-C-[(indol-3-yl)methyl]-a- -
L
(1a),
L
Earlier we demonstrated that 1a, by heating
L
at pHB3 in water, dissociates to
L-ascorbic
conditions (room temperature, buffer at pH
4.2).1–3 Ascorbigen is the most abundant in-
dole-derived dietary ingredient, which humans
or animals obtain with cruciferous vegeta-
bles.4,5 The anticarcinogenic properties re-
ported for cruciferous vegetables,6 makes
studies on chemical and biological properties
of ascorbigen important. Ascorbigen is a
acid and an unstable salt of 3-methyleneindo-
lenine, which oligomerizes to give di(indol-3-
yl)methane,
5,11H-indolo[3,2-b]carbazole,
and some other oligomers, or it interacts with
another molecule of ascorbigen to yield 2%-[(in-
dol-3-yl)methyl]ascorbigen.7 These products
are capable of further transformations in acid
media.
At pH\7 ascorbigen is also unstable:
opening of the lactone ring leads to 2-C-[(in-
dol-3-yl)methyl]-a- -xylo-hex-3-ulofurano-
* Corresponding author.
E-mail address: lcta@space.ru (M.N. Preobrazhenskaya).
L
0008-6215/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(00)00310-4

470
A.M. Korole6 et al. / Carbohydrate Research 330 (2001) 469–477
sonic acid (2), which spontaneously decar-
droxy-4-hydroxymethyl-3-(indol-3-yl)cyclo-
pent-2-enone (5a) was formed in 10–15%
yield. Racemic N-substituted indolylcyclopen-
tenone derivatives (N-methyl-, 5b; N-benzyl-,
5c; N-hexyl-, 5e; and N-methoxy-, 5f) were
obtained under these conditions in higher
yields (Scheme 2, Table 1).
boxylates and, after isomerization, produces a
mixture of 1-deoxy-1-(indol-3-yl)-a- -sorbo-
L
pyranose (3) and 1-deoxy-1-(indol-3-yl)-a-
L
-
tagatopyranose (4) (Scheme 1).8
The goal of this work was to study the
transformations of ascorbigen in acid media,
which proceed without the release of -ascor-
L
Mild reaction conditions and the availabil-
bic acid and lead to indole derivatives of a
new type.
ity of reagents (starting ascorbigens and
L
-
ascorbic acid) make these cyclopentenone
derivatives 5 readily available, and the intense
fluorescence of these compounds facilitated
their TLC analysis and chromatographic
purification. The presence of ascorbic acid in
this reaction is crucial, as the heating of the
unsubstituted ascorbigen (1a) or its N-benzyl-
(1c) derivative at pH51 in a 1:1 methanol–1
N HCl mixture (Method B) yielded strongly
fluorescent cyclopentenones (5a and 5c) in a
very low yields (Table 1).
1-Alkoxyascorbigens, which were obtained
by the methods reported in Refs. 10, 11, un-
dergo similar transformations. In a boiling
methanol–1 N HCl solution, 1f and 1g were
converted into the corresponding highly
fluorescent 2-hydroxy-3-(1-alkoxyindol-3-yl)-
2. Results and discussion
When ascorbigen is incubated in a warm
-ascorbic acid solution, the dissociation to
-ascorbic acid and 3-methylenindolenine
L
L
oligomers is supressed. This facilitates a new
type of reaction, which represents a sequential
combination of such simple transformations
as hydrolysis, CO2 extrusion, dehydration, cy-
clization or Michael addition, and isomeriza-
tion and is called a domino reaction.9 When a
solution of 1a was heated at 60 °C in an
aqueous solution of
L
-ascorbic acid (at a mo-
lar ratio 1:10–20) (Method A) racemic 2-hy-
Scheme 1.

A.M. Korole6 et al. / Carbohydrate Research 330 (2001) 469–477
471
Scheme 2. 5a R=H; 5b R=CH3; 5c R=CH2C6H5; 5d R=CH2CHꢀCH2; 5e R=C6H13; 5f R=OCH3; 5g R=OC2H5.
When a reaction was performed with (indol-
4-hydroxymethylcyclopent-2-enones (5f and
5g) in 10–15% yields, whereas in a hot solu-
3-yl)glycolic acid methyl ester 9 and -ascor-
L
bic acid, one of the isomers of the unstable
tion of -ascorbic acid the yield of 5f reached
L
2-C-[(indol-3-yl)(methoxycarbonyl)methyl]-a-
27%. Earlier we have demonstrated that 1-
alkoxyascorbigens are more stable in acids
than ascorbigen 1a, and need more drastic
L
-xylo-hex-3-ulosonic acid 1,4-lactone (10)
was isolated (Scheme 4). This result supports
the suggestion that carboxyascorbigen deriva-
tives 8 are intermediates in the reactions of
alkylindolylglycolic and ascorbic acids. Ester
10, when stored for 1 h, underwent decompo-
sition with the formation of several uniden-
tified products. The 1H NMR data correspond
conditions for the release of
L
-ascorbic acid
and the formation of 1-alkoxyindolylmethyl
oligomers.12 This explains the higher yields of
cylopentenone derivatives 5f and 5g in acid
conditions in comparison with 5a. Compari-
son of yields of cyclopentenones obtained by
Methods A and B shows that the presence of
bulky N-substituents on the indole ring, which
hinders the oligomerization reaction, facili-
tates the formation of cyclopentenones; the
second important factor facilitating the cy-
to an (indol-3-yl)methyl derivative of -xylo-
L
hex-3-ulosono-1,4-lactone, but do not estab-
lish whether the cyclic 3,6-hemiacetal furanose
ring is present in compound 10.
HR-MS of compounds 5a–g revealed peaks
1
for molecular ions. The H and 13C NMR
clopentenone formation is the excess of
L
-
spectral parameters of the cyclopentenone
moieties in compounds 5 (Tables 2 and 3) are
similar to those of the previously described
2-hydroxy-3-(4-hydroxy-3-methoxyphenyl)-4-
hydroxy-methylcylopent-2-enone (6).13
To understand the mechanism of transfor-
mation of ascorbigens into cyclopentenone
ascorbic acid, which hinders the release of
acid from ascorbigen.
Another method for preparation of indolyl-
cyclopentenone derivatives uses (indol-3-
yl)glycolic acids as starting compounds.
Earlier we obtained 2-hydroxy-4-hydrox-
ymethyl-3-(4-hydroxy-3-methoxyphenyl)cyclo-
pent-2-enone (6) by the interaction of vanillo-
mandelic and ascorbic acids.13 By the treat-
ment of indolylglycolic acids 7a–e in a hot
Table 1
Comparison of yields of compounds 5 obtained by Methods
A, B, and C
aqueous solution of
L
-ascorbic acid (10–12
Compound
Yield (%)
Method A
equiv), we obtained cyclopentenone deriva-
tives 5a–e in 30–40% yields (Table 1, Method
C). The presumed intermediate ascorbigens
8a–e were not observed (Scheme 3). The start-
ing (indol-3-yl)glycolic acid and its N-methyl-,
N-benzyl-, and N-allyl- and N-n-hexyl deriva-
tives 7a–e were prepared from the corre-
sponding (indol-3-yl)glyoxylic acids by the
method described.14
Method B
Method C
5a
5b
5c
5d
5e
5f
15
25
41
2
5
17
30
39
32
30
40
27
15
15
5g

Table 2
1H NMR spectral data (l ppm, J Hz) for 5a–g (CD3OD)
Signals
5a
5b
5c
5d
5e
5f
5g
a
4-CH
3.75
3.67 a
3.70 a
3.72 a
3.73 a
3.72 a
3.70 a
5-CH2
2.56 a;
2.61 a;
2.63 a;
2.65 a;
2.65dd;
2.45d;
2.68 a;
2.64 a;
2.45 a;
2.43 a;
2.47 a;
2.48 a;
2.45 a;
2.47 a;
J5a,5b 18.6;
J4,5a 1.0;
J4,5b 6.0
J5a,5b 18.6;
J4,5a 0;
J4,5b 6.2
J5a,5b 18.8;
J4,5a 0;
J4,5b 6.1
J5a,5b 18.6;
J4,5a 0.9;
J4,5b 6.3
J5a,5b 18.8;
J4a,5aꢀ0;
J4,5b 6.0
J5a,5b 18.6;
J4,5a 0.8;
J4,5b 6.2
J5a,5b 18.3;
J4,5a 0;
J4,5b 6.1
/
6-CH2
Indole
4.08 a;
4.00 a;
4.04 a;
4.04 a;
4.07dd;
3.41dd;
J6a,6b 10.7;
J4,6a 3.2;
J4,6b 7.7
4.02 a;
4.06 a;
3.42 a;
3.41 a;
3.50 a;
3.51 a;
3.43 a;
3.41 a;
J6a,6b 10.7;
J4,6a 3.0;
J4,6b 7.6
J6a,6b 10.9;
J4,6a 3.2;
J4,6b 7.5
J6a,6b 10.8;
J4,6a 2.7;
J4,6b 7.3
J6a,6b 10.7;
J4,6a 3.1;
J4,6b 7.4
J6a,6b 10.7;
J4,6a 3.1;
J4,6b 7.2
J6a,6b 10.8;
J4,6a 3.0;
J4,6b 7.6
3
7.13 (1 H, t, 5%-H); 7.14 (1 H, t, 5%-H); 7.10 (1 H, t, 5%-H); 7.18 (1 H, t, 5%-H); 7.19 (1 H, t, 5%-H); 7.22 (1 H, t, 5%-H); 7.17 (1 H, t, 5%-H);
7.18 (1 H, t, 6%-H); 7.21 (1 H, t, 6%-H); 7.15 (1 H, t, 6%-H); 7.24 (1 H, t, 6%-H); 7.22 (1 H, t, 6%-H); 7.32 (1 H, t, 6%-H); 7.26 (1 H, t, 6%-H);
7.43 (1 H, d, 7%-H); 7.30 (1 H, d, 7%-H); 7.30 (1 H, d, 7%-H); 7.33 (1 H, d, 7%-H); 7.46 (1 H, d, 7%-H); 7.53 (1 H, d, 7%-H); 7.45 (1 H, d, 7%-H);
7.95 (1 H, d, 4%-H); 7.84 (1 H, d, 4%-H); 7.90 (1 H, d, 4%-H); 7.88 (1 H, d, 4%-H); 7.95 (1 H, d, 4%-H); 7.95 (1 H, d, 4%-H); 7.93 (1 H, d, 4%-H);
8.12 (1 H, s, 2%-H). 7.95 (1 H, s, 2%-H). 8.08 (1 H, s, 2%-H). 8.00 (1 H, s, 2%-H). 8.10 (1 H, s, 2%-H). 8.24 (1 H, s, 2%-H). 8.18 (1 H, s, 2%-H).
(
protons b
469
477
a (1 H, m).
2
3
2
b N-substituents: 5b, CH3 3.77 (3 H, s); 5c, CH2C6H5 5.32 (2 H, s), 7.30–7.15 (5 H, m); 5d, CH2CHꢀCH2 4.75 (2 H, bd, J 5.5, H-1%%), 5.20 (1 H, dd, J 10.2, J 1.1, Ha-3%%);
3
2
5.11 (1 H, dd, J 17.1, J 1.1, HB-3%%); 5.96 (1 H, m, H-2%%); 5e, C6H13 0.88 (3 H, bs); 1.32 (8 H, m); 3.02 (2 H, t); 5f, OCH3 4.15 (3 H, s); 5g, OC2H5 4.34 (2 H, q), 1.41
(3 H, t).

A.M. Korole6 et al. / Carbohydrate Research 330 (2001) 469–477
473
Scheme 3.
Scheme 4.
derivatives, the gradual transformation of
ascorbigen under mild conditions was investi-
gated. Compound 1a was dissolved in an tri-
When ascorbigen is incubated in warm
ascorbic acid solution, opening of the lactone
ring as the first step of the reaction is not
feasible. In this case, the furanose ring may
open first to give lactone 14 (Scheme 6) fol-
lowed by the extrusion of CO2 and dehydra-
tions, which give the key intermediate
pentadienone 12.
ethylamine–water
solution;
after
its
transformation into the salt of the acid 2a was
complete (as monitored by TLC), the mixture
was acidified to pH 2 with HCl. This pre-
vented the transformation of 2a into 1-deoxy-
1-indolylketoses 3 and 4 and resulted in
several new products, which were separated by
gel-column chromatography on Sephadex LH-
20 with methanol as eluent. 2,5,6-Trihydroxy-
In conclusion, this work describes a new
type of ascorbigen transformation that leads
to (indol-3-yl)cyclopentenone derivatives.
1-(indol-3-yl)hex-1-en-3-one
(11),
2,6-
dihydroxy-1-(indol-3-yl)hexa-1,4-dien-3-one
(12), and 2-hydroxy-4-hydroxymethyl-5-(in-
dol-3-yl)cyclopent-2-enone (13) were isolated.
When stored or heated, 12 formed 13, which
spontaneously gave cyclopentenone 5a. The
scheme of formation of 11, 12, and then 13
from the acid 2a possibly includes an opening
of the furanose ring, followed by decarboxyla-
tion and subsequent dehydrations (Scheme 5).
3. Experimental
General methods.—NMR spectra were
recorded with a Varian VXR-400 instrument
operated at 400 MHz (1H NMR) or at 100.6
MHz (13C NMR). Chemical shifts were mea-
sured in CD3OD or CDCl3 using these sol-
vents as internal standards (CDCl3: l 1H
(residual) 7.25 ppm, 13C 77.00 ppm; CD3OD:

474
A.M. Korole6 et al. / Carbohydrate Research 330 (2001) 469–477
Table 3
13C NMR spectra of compounds 5b,e,f (chemical shifts,
ppm) a
5b in
5e in CD3OD 5f in CD3OD
CD3OD+CDCl3
Cyclopentenone ring
C-1
C-2
C-3
C-4
C-5
C-6
200.55
146.25
137.16
38.68
36.46
65.28
202.34
148.21
141.65
40.06
37.63
66.44
202.51
148.77
140.19
40.10
37.69
66.18
Scheme 6.
(E. Merck), and column chromatography on
Silica Gel Merck 60 (E. Merck) in the same
system. Electron impact mass-spectra were ob-
tained on an SSQ 710 Finnigan instrument.
2-Hydroxy-3-(indol-3-yl)-4-hydroxymethyl-
cyclopent-2-enone (5a) (Method A).—An
aqueous solution (20 mL) containing ascorbi-
Indole ring
C-2%
C-3%
C-4%
125.78
108.83
120.99
127.41
110.11
122.40
129.84
121.76
123.22
111.29
133.45
127.23
107.16
122.7
130.54
122.47
124.14
109.73
133.51
C-4%a 131.21
C-5%
C-6%
C-7%
120.93
122.30
109.80
gen 1a (0.1 g, 0.32 mmol) and -ascorbic acid
L
C-7%a 133.21
(1.15 g, 6.55 mmol) was stirred at 60 °C for 2
days. After cooling, the methyleneindolenine-
derived polymeric side products were filtered
off, and the filtrate was extracted with EtOAc.
The extract was dried over Na2SO4 and evap-
orated, and the residue was purified by
column chromatography, using as eluents con-
secutively CHCl3 and CHCl3–MeOH (25:1
a N-Substituents: 5b 33.05. 5e 14.29; 23.57; 27.57; 31.06;
32.52; 47,55. 5f 66.92 ppm.
1
l H (residual) 3.32 ppm, 13C 49.00 ppm).
Analytical TLC was performed on Kieselgel
F254 plates, and preparative TLC on plates
(20×20 cm, 0.5 mm) with Kieselgel 60 F254
Scheme 5.

A.M. Korole6 et al. / Carbohydrate Research 330 (2001) 469–477
475
3-(1-Benzylindol-3-yl)-2-hydroxy-4-hydroxy-
methylcyclopent-2-enone (5c) (Method C).—A
solution of (1-benzylindol-3-yl)glyoxyalic acid
(170 mg, 0.6 mmol) in 80% aq EtOH (15 mL)
was treated with a threefold excess of NaBH4
(80 mg). After 1 h, the reaction mixture, con-
taining 2c was filtered and and the filtrate
added dropwise to an aq solution (30 mL) of
and then 10:1) to afford 10 mg (12.5%) of
5a as a greenish amorphous powder, Rf 0.45
(5:1, CHCl3–MeOH); HR-MS, m/z: Found
243.0870, determined for C14H13NO3 243.0895;
Anal. Calcd for C14H13NO3: C, 69.12; H, 5.39;
N, 5.76. Found: C, 69.00; H, 5.49; N.5.59.
The EIMS of the per-(Me3Si) derivative
obtained from 5a in boiling HMDS, m/z:
387 (3%) [C14H13NO3]+, 315 (35%) [C14H13NO3-
(SiMe3)2−SiMe3]+, 243 (4%) [C14H13NO3-
(SiMe3)2−2SiMe3]+, 73 (100%) [SiMe3]+.
2-Hydroxy-4-hydroxymethyl-3-(1-methylin-
dol-3-yl)-cyclopent-2-enone (5b) was obtained
similarly and isolated as a greenish amor-
phous powder. Rf 0.47 (in EtOAc); HR-MS,
m/z: Found 257.1062; Anal. Calcd for
C15H15NO3, 257.1052; MS of the per-(Me3Si)
derivative, m/z: 401 (5%) [C15H13NO3
(SiMe3)2]+, 386 (5%) [C15H13NO3(SiMe3)2−
Me]+, 329 (60%) [C15H14NO3 (SiMe3)]+, 257
(20%) [C15H15NO3]+; 73 (100%) [SiMe3]+.
2-Hydroxy-4-hydroxymethyl-3-(1-benzylin-
dol-3-yl)-cyclopent-2-enone (5c) was obtained
similarly: Rf 0.60 (EtOAc). HR-MS, m/z:
Found 333.1386; Anal. Calcd For C21H19NO3
333.1365; MS of the per-(Me3Si) derivative,
m/z: 477 (30%) [C21H17NO3 (SiMe3)2]+, 405
(4%) [C21H18NO3 (SiMe3)]+, 332 (1%)
[C21H19NO3−H]+; 91 (80%) [C6H5CH2]+, 73
(100%) [SiMe3]+.
3-(1-Hexylindol-3-yl)-2-hydroxy-4-hydroxy-
methylcyclopent-2-enone (5e) was obtained
similarly: Rf 0.63 (EtOAc); MS of the per-
(Me3Si) derivative, m/z: 471 (35%) [C20H23NO3
(SiMe3)2]+, 456 (15%) [C20H23NO3 (SiMe3)2−
Me]+, 399 (20%) [C20H24NO3 (SiMe3)]+,
370 (4%) [C20H24NO3 (SiMe3)−C2H5]+; 73
(100%) [SiMe3]+; Anal. Calcd for C20H25NO3:
C, 73.37; H, 7.70; N, 4.28. Found: C, 73.15;
H, 7.80; N, 4.14.
2-Hydroxy-4-hydroxymethyl-3-(1-methoxyl-
indol-3-yl)cyclopent-2-enone (5f) was obtained
by the same method; Rf 0.60 (EtOAc); MS of
the per-(Me3Si) derivative, m/z: 417 (1%)
[C15H13NO4 (SiMe3)2]+, 402 (1%) [C14H10NO4
(SiMe3)2−Me]+, 387 (3%) [C14H10NO3
(SiMe3)−OMe+H]+, 345 (1%) [C15H11NO4
(SiMe3)]+; 73 (100%) [SiMe3]+; Anal. Calcd.
for C15H15NO4: C, 65.92; H, 5.53; N, 5.13.
Found: C, 65.99; H, 5.63; N, 5.10.
L-ascorbic acid (1 g, tenfold excess), and
refluxed for 20 h. The solution was separated
from oil drops, cooled, and extracted with
CHCl3. The organic layer was dried (Na2SO4)
and evaporated to give the crude product,
which was purified by flash chromatography
in 5:1 petroleum ether–EtOAc and then in
EtOAc to yield 5c as an amorphous solid
(39%); Rf 0.60 (EtOAc). The compound was
identical to the sample obtained by Method
A.
3-(1-Allylindol-3-yl)-2-hydroxy-4-hydroxy-
methylcyclopent-2-enone (5d) was obtained
similarly; Rf 0.57 (EtOAc); HR-MS, m/z:
Found 283.1200, Anal. Calcd for C17H17NO3
283.1208.
3-(1-Ethoxyindol-3-yl)-2-hydroxy-4-hydroxy-
methylcyclopent-2-enone (5g) (Method B).—
A solution of 1g (100 mg) in 10 mL of
1:1 MeOH–aqueous HCl was stirred at
60 °C for 6 h. Water and EtOAc were then
added. The organic layer was dried (Na2SO4),
evaporated in vacuo, and purified by TLC (Rf
0.60) to give 13 mg (15%) of an amorphous
solid; Rf 0.60 (EtOAc); HR-MS, m/z: Found
287.1169, Anal. Calcd for C16H17NO4
287.1158; MS of the per-(Me3Si) derivative,
m/z: 431 (2%) [C16H15NO4 (SiMe3)2]+, 387
(3%) [C16H15NO4(SiMe3)2-OEt+H]+, 359
(2%) [C16H16NO4 (SiMe3)]+, 73 (100%)
[SiMe3]+.
2-C-[(Indol-3-yl)(methoxycarbonyl)methyl]-
h- -xylo-hex-3-ulofuranosonic acid 1,4-lactone
L
(10).—The methyl ester (9) of (indol-3-
yl)glycolic acid (102 mg, 0.5 mmol) was added
to a solution of -ascorbic acid (270 mg, 1.5
L
mmol) in aq MeOH. The mixture was stirred
for 2 days at 50 °C, and then diluted with
water and extracted with EtOAc. The extract
was dried (Na2SO4) and the crude product,
purified by TLC to give 15 mg (8%) of amor-
1
phous 10; Rf 0.32 (8:1, CHCl3–MeOH); H

476
A.M. Korole6 et al. / Carbohydrate Research 330 (2001) 469–477
13C NMR (CD3OD): 195.61; 147.07; 137.54;
130.18; 128.38; 123.26; 121.07; 119.19; 112.53;
111.59; 109.79; 70.80; 66.89; 40.29 ppm; Anal.
Calcd. for C14H15NO4: C, 64.36; H, 5.79; N
5.36. Found: C, 64.48; H, 5.83; N 5.20. Like-
wise 20 mg (8%) of 2-hydroxy-4-hydrox-
ymethyl-5-(indol-3-yl)cyclopent-2-enone (13)
was isolated similarly as a slightly yellow pow-
der. Rf 0.42 (7:2, CHCl3–MeOH). HR-MS:
NMR in CD3OD, indole moiety: 7.70 (1 H, d,
H-4%), 7.50 (1 H, s, H-2%), 7.36 (1 H, d, H-7%),
7.11(1 H, t) and 7.05 (1 H, t) (H-5% and H-6%);
CHꢁCOOMe: 4.51 (1 H, s); ascorbic acid
moiety: 4.58 (1 H, d, J4,5 1.0 Hz, H-4), 4.40 (1
H, m, H-5), 4.16 (1 H, dd, J5,6a 5.6 Hz, H-6a),
4.00 (1 H, dd, J5,6b 3.6, J6b,6a 9.7 Hz, H-6b);
3.64 (3 H, s, OCH3) ppm.
Gradual transformation of ascorbigen 1a.—
To a solution of ascorbigen 1a (305 mg, 0.1
mmol) in 9 mL of 1:2 MeOH–water was
added Et3N (0.27 mL, 0.2 mmol). After the
transformation of 1a into the ascorbigen acid
salt was complete (10–15 min, Rf of the acid
salt ꢀ0 in 7:2 CHCl3–MeOH), 1 N HCl was
added to pH 2 and the reaction mixture was
stirred under heating at 50 °C for 45 min. The
mixture was extracted with CHCl3, the extract
was washed repeatedly with brine until the
washings came to neutral pH, dried (Na2SO4)
and concentrated in vacuum. The residue was
loaded onto a column of Sephadex LH-20 and
the compounds 11, 12, and 13 were eluted
with MeOH. The fractions containing 12 were
evaporated to give, after evaporation, 50 mg
(20%) of the amorphous 2,6-dihydroxy-1-(in-
dol-3-yl)hexa-1,4-dien-3-one, which was stored
under Ar at −17 °C; it was a bright orange
powder; Rf 0.70 (7:2, CHCl3–MeOH); HR-
MS: 243.0880; Anal. Calcd for C14H13NO3
1
243.0876 Calc. for C14H13NO3: 243.0895; H
NMR (CD3OD+CDCl3), cyclopentenone
ring: 3.08 (1 H, m, J4,5 2.38 Hz, H-4); 3.55 (1
H, d, J4,5 2.38 Hz, H-5); 3.66 (1 H, dd, J6a,6b
10.84 Hz, H-6a); 3.79 (1 H, dd, J6a,6b 10.84
Hz, H-6b); 6.62 (1 H, d, J3,4 2.74 Hz, H-3);
indole ring: 8.14 (1 H, s); 7.33 (1 H, t), 7.08 (2
H, m); 6.96 (1 H, t). Anal. Calcd for
C14H13NO3: C, 69.12; H, 5.39; N, 5.76. Found:
C, 68.90; H, 5.49; N.5.56. When the reaction
mixture, after addition of HCl, was heated for
90 min at 50 °C, cyclopentenone 13 was
isolated in an amount of 40 mg (16%). It
was also obtained by heating or by storing of
12.
References
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1
243.0895; H NMR (CD3OD+CDCl3): 7.18
(1 H, s, H-1); 7.30 (1 H, dt, J4,5 15.42 Hz,
H-4); 7.06 (1 H, dt, J5,6 3.98 Hz, H-5); 4.39 (2
H, q, J6,4 2.11 Hz, H-6); indole ring: 7.83 (1 H,
d, H-4%); 7.41 (1 H, d, H-7%), 7.19 (1 H, td,
H-6%), 8.04 (1 H, s, H-2%), 7.15 (1 H, td, H-5%)
ppm. 13C NMR (CD3OD+CDCl3): 185.60;
147.59; 146.71; 137.53; 130.65; 128.33; 123.34;
121.57; 121.22; 119.11; 112.58; 111.78; 110.08;
62.56 ppm.
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mg (16%) as a yellow powder, Rf 0.52 (7:2,
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