Development of a stereoselective practical synthetic route to indolmycin, a candidate anti-H. pylori agent

Article abstract of DOI:10.1248/cpb.49.1604

A stereoselective practical synthetic route to indolmycin is described. The route is composed of the regioselective coupling of indolyl magnesium halide with a trans-epoxy ester, diastereoselective oxazolone ring formation with guanidine and amine exchang

Full text of DOI:10.1248/cpb.49.1604

1604
Chem. Pharm. Bull. 49(12) 1604—1608 (2001)
Vol. 49, No. 12
Development of a Stereoselective Practical Synthetic Route to Indolmycin,
a Candidate Anti-H. pylori Agent
Atsushi HASUOKA,a Yutaka NAKAYAMA,a Mari ADACHI,b Hidenori KAMIGUCHI,c and Keiji KAMIYAMA*,a
Medicinal Chemistry Research Laboratories I,a Medicinal Chemistry Research Laboratories II,b and Drug Analysis &
Pharmacokinetics Research Laboratories,c Takeda Chemical Industries Ltd., 2–17–85 Jusohonmachi, Yodogawa-ku, Osaka
532–8686, Japan. Received August 3, 2001; accepted September 17, 2001
A stereoselective practical synthetic route to indolmycin is described. The route is composed of the regiose-
lective coupling of indolyl magnesium halide with a trans-epoxy ester, diastereoselective oxazolone ring formation
with guanidine and amine exchange reaction with methylamine. In the coupling step, use of dichloromethane as
co-solvent and conversion of the resulting hydroxy ester to the hydroxy acid for purification, make this process
efficient and practical. The oxazolone ring is formed in good yield without epimerization at the C5 position by
treatment with guanidine and potassium tert-butoxide in tert-butanol at room temperature. In the final step, the
amino group is efficiently converted to the methylamino group in aqueous methylamine solution at 5 °C. After ex-
amination of the route with racemates, indolmycin was synthesized stereoselectively in 22% total yield from opti-
cally active trans-epoxy ester. This route was applied to the preparation of the metabolites of indolmycin.
Key words indolmycin; diastereoselective synthesis; metabolite; amine exchange; guanidine
Indolmycin (1), isolated from an African strain of Strepto- dolyl magnesium bromide in ethyl ether and dichloromethane
myces albus,1) exhibits antibacterial activity against Staphylo- gave (Ϯ)-2 in a better yield of 65%. By increasing the
cocci.2) Recently, our screening group found that 1 also has amount of methyl magnesium bromide (2.2 eq to 3) the yield
potent antibacterial activity against Helicobacter pylori (H. was improved to 79% (Chart 2). Although the yield was sat-
pylori) and it is a promising anti-H. pylori agent.3)
isfactory, it was necessary to purify the crude product by sil-
Although syntheses of 1, including its racemate, have been ica gel column chromatography to remove unreacted indole
reported by several groups,4) none of them is satisfactory for and by-products. As it was found that the hydroxy acid (Ϯ)-4
large scale synthesis because of low diastereoselectivity or was easily purified by extraction and recrystallization, crude
involving too many chemical processes. Therefore, it was (Ϯ)-2 was hydrolyzed to (Ϯ)-4 and after purification, esteri-
necessary to develop a stereoselective practical synthetic fication of (Ϯ)-4 gave pure (Ϯ)-2 (Chart 2). Thus we accom-
route to 1 for further study. In this paper, we wish to report a plished the preparation of the racemic hydroxy ester (Ϯ)-2.
convenient and practical stereoselective synthesis of 1 from
Formation of the Oxazolone Ring Although Schach
epoxy ester 3 as a starting material, through hydroxy ester 2 von Wittenau and Els4e) and Preobrazhenskaya et al.4a) re-
(Chart 1), and we show its application to the preparation of ported that (Ϯ)-1 was prepared through formation of an oxa-
metabolites.
zolone ring with N,NЈ-dimethylguanidine from the hydroxy
ester (Ϯ)-2, the yields were very low, partly because the
epimerization at C5 position of the oxazolone ring occurred
Chemistry
Preparation of an Intermediate Hydroxy Ester (؎)-2 in the alkaline medium. After intensive examination of the
Initially we started to study the diastereoselective synthesis reaction, we found that epimerization was suppressed in tert-
of (Ϯ)-1 from (Ϯ)-3 which was easily prepared from ethyl butanol below room temperature but the reaction was very
crotonate by oxidation with m-chloroperbenzoic acid. We in- slow (data was not shown). Therefore, we gave up the prepa-
vestigated the condensation of indolyl magnesium halide ration of (Ϯ)-1 from the hydroxy ester (Ϯ)-2 in one step.
with (Ϯ)-3 although the coupling reaction of (Ϯ)-3 with in-
Guanidine was expected to react faster than N,NЈ-di-
dole in the presence of Lewis acid was reported.4e) Indole methylguanidine with (Ϯ)-2 to afford the amino derivative
was treated with methyl magnesium bromide in ethyl ether to (Ϯ)-5.4a) Therefore, we examined a 2 step conversion from
form indolyl magnesium bromide and the complex was iso- (Ϯ)-2 to (Ϯ)-1: the formation of the oxazolone ring with
lated. Addition of (Ϯ)-3 to the reaction mixture gave the de- guanidine followed by an amine exchange reaction. Based on
sired hydroxy ester (Ϯ)-2 in 48% yield after purification with
silica gel column chromatography. The moderate yield was
due to poor solubility of indolyl magnesium bromide in ethyl
ether. It was reported that addition of dichloromethane to in-
dolyl magnesium halide in ethyl ether brought the complex
into a clear solution.5) Addition of (Ϯ)-3 to a solution of in-
Chart 1
Chart 2
To whom correspondence should be addressed. e-mail: Kamiyama_Keiji@takeda.co.jp
© 2001 Pharmaceutical Society of Japan

December 2001
1605
Table 1
Run
Guanidine
tert-BuOK
(Ϯ)-2a)
(Ϯ)-5a)
(Ϯ)-6a)
1
2
3
2.0 eq
3.5 eq
5.0 eq
2.1 eq
3.7 eq
5.3 eq
23
2
Ͻ1
59
83
86
3
2
3
Chart 3
a) HPLC yield based on (Ϯ)-2.
Table 2
Run
Solvent
Temp. (°C)
Time (h)
(Ϯ)-1a)
(Ϯ)-7a)
1
2
3
CH3OH
CH3OH
H2O
5
25
5
24
6
4
84
86
93
5
5
3
Chart 4
a) HPLC yield based on (Ϯ)-5.
stereoselectively in good yield from the racemic trans-epoxy
ester (Ϯ)-3. Then, we confirmed that this synthetic route was
efficient for large-scale preparation of optically active in-
dolmycin 1 from the optically active (ϩ)-3. Some prepara-
tions of the optically active trans-epoxy ester (ϩ)-3 have
been reported.6)
the information obtained above, the reaction was performed
at room temperature with potassium tert-butoxide as base
and tert-butanol as solvent (Table 1). Although the starting
material still remained after 24 h with 2 eq of guanidine (run
1), the ratio of (Ϯ)-5 to its diastereomer (Ϯ)-6 was satisfac-
torily high (ca. 20 : 1). By increasing the amount of guani-
dine and potassium tert-butoxide (runs 2, 3) we obtained
(Ϯ)-5, almost diastereoselectively in 86% yield in 24 h.
Amine Exchange Reaction It has been reported that the
2-(dimethylamino)-4(5H)-oxazolone derivative of (Ϯ)-1 was
converted to (Ϯ)-1 quantitatively in liquid methylamine
without significant epimerization.4c) Although a similar
amine exchange reaction was expected to occur in the case of
(Ϯ)-5, the amino group was not transformed into the methyl-
amino group under the same conditions. Next we treated
(Ϯ)-5 with commercially available 40% methylamine solu-
tion in methanol at 5 °C for 24 h and (Ϯ)-1 was obtained in
84%, with 5% of its diastereomer (Ϯ)-7 (Table 2). Although
higher temperature (25 °C) accelerated the reaction, the ratio
of (Ϯ)-1 to (Ϯ)-7 was not improved. Treatment of (Ϯ)-5
with commercially available 40% methylamine in water at
5 °C for 4 h afforded (Ϯ)-1 in 93% with only 3% of its di-
astereomer (Ϯ)-7.
Treatment of the epoxy ester (ϩ)-3 (93.3% ee) with in-
dolyl magnesium bromide in ethyl ether and dichloromethane
followed by hydrolysis afforded the crude acid (Ϫ)-4. After
recrystallization from water, pure (Ϫ)-4 was obtained in 51%
yield which was lower than for the racemate due to loss dur-
ing recrystallization. Esterification of (Ϫ)-4 gave practically
pure (ϩ)-2 quantitatively as a syrup. Treatment of (ϩ)-2 with
guanidine in tert-butanol under the reaction conditions de-
scribed above afforded the pure amino derivative (Ϫ)-5 in
67% after crystallization from ethyl acetate. Finally (Ϫ)-5
was treated with 40% methylamine solution in water at 5 °C
to give crude indolmycin 1, which was recrystallized from
methanol–water to afford pure indolmycin 1 (99.4% ee, total
yield 22% from (ϩ)-3). Thus the stereoselective practical
synthetic route to 1, shown in Chart 3, was established.
Synthesis of Metabolites of Indolmycin Five metabo-
lites shown in Chart 4 were detected in rat serum and/or exc-
reta after oral administration of indolmycin and were charac-
terized by liquid chromatography/ion–trap mass spectrome-
Total Synthesis of Optically Active Indolmycin 1 As
described above, racemic indolmycin was synthesized dia-
1
try (LC/IT/MS) and H-NMR. M-I is the 6-hydroxy deriva-

1606
Vol. 49, No. 12
Chart 8
large-scale in 5 steps, with high purity, from the optically ac-
tive epoxy ester (ϩ)-3. Moreover, this route is useful for
preparation of the metabolites of 1.
Chart 5
Experimental
1H-NMR spectra were recorded on a Varian Gemini 200 (200 MHz) with
tetramethylsilane as an internal standard and chemical shifts (d) are ex-
pressed in ppm. The following abbreviations are used; s: singlet, d: doublet,
t: triplet, q: quartet, br s: broad singlet, dd: double doublet, dt: double triplet,
dq: double quartet, m: multiplet. Infrared absorption spectra (IR) were mea-
sured on a FTIR-8200PC type IR spectrophotometer made by Shimadzu. El-
emental analyses were performed by Takeda Analytical Research Laborato-
ries, Ltd. Optical rotations were recorded on a DIP-370 digital polarimeter
made by JASCO. Melting points were determined using a Micro Melting
Point Apparatus made by Yanaco. Kieselgel 60 made by Merck was used as
the support for column chromatography.
(2S,3R)-2-Hydroxy-3-(1H-indol-3-yl)butanoic Acid ((؊)-4) To a solu-
tion of methyl magnesium bromide in ethyl ether (2.93 M, 35 ml) was added
indole (5.86 g, 50.0 mmol) in 50 ml of dichloromethane, dropwise over
45 min under N2 atmosphere at 0 °C. After stirring for 30 min, the solution
was cooled to Ϫ20 °C and then ethyl (2S,3R)-2,3-epoxybutanoate ((ϩ)-3,
5.47 g, 42.0 mmol) in dichloromethane (50 ml) was added dropwise over
1.5 h at Ϫ20 °C. After stirring for 1 h, 1 N HCl (150 ml) was added. The or-
ganic layer was separated and the aqueous layer was extracted with
dichloromethane (50 ml). The combined organic layer was dried over anhy-
drous MgSO4 and concentrated in vacuo. To the residue were added ethanol
(60 ml) and 1 N NaOH (75 ml) and the mixture was stirred for 16 h at room
temperature. After removal of the solvent by evaporation, water (60 ml) was
added and the aqueous solution was washed with ethyl acetate (100 ml)
twice. The aqueous layer was adjusted to pH 2—3 with 4 N HCl and ex-
tracted with ethyl acetate (100 ml) twice. The combined extract was dried
over anhydrous MgSO4 and evaporated under reduced pressure. The residue
was recrystallized from water (80 ml) to give (2S,3R)-2-hydroxy-3-(1H-
indol-3-yl)butanoic acid ((Ϫ)-4, 4.72 g, 51%). 1H-NMR (DMSO-d6) d: 1.25
(3H, d, Jϭ7.0 Hz), 3.41 (1H, m), 4.19 (1H, d, Jϭ4.6 Hz), 6.93—7.14 (3H,
m), 7.33 (1H, d, Jϭ7.4 Hz), 7.54 (1H, d, Jϭ7.4 Hz), 10.79 (1H, br s). IR
(KBr, cmϪ1): 3429, 3397, 1726, 1458. Anal. Calcd for C12H13NO3: C, 65.74;
H, 5.98; N, 6.39. Found: C, 65.48; H, 6.10; N, 6.34. [a]D22 Ϫ9.3° (cϭ2.0,
methanol) [lit.4e) [a]D25 Ϫ10° (cϭ2.0, methanol)]. mp 180.5—181 °C (lit.4e)
181—182 °C).
Ethyl (2S,3R)-2-Hydroxy-3-(1H-indol-3-yl)butanoate ((؉)-2) Acetyl
chloride (15 ml, 211 mmol) was added to ethanol (75 ml) at 0 °C. After stir-
ring for 30 min, (2S,3R)-2-hydroxy-3-(1H-indol-3-yl)butanoic acid ((Ϫ)-4,
4.42 g, 20.2 mmol) was added at 0 °C. The solution was stirred for 6 h at
room temperature. After removal of the solvent, the residue was dissolved
into ethyl acetate (150 ml). The organic layer was washed with aqueous satu-
rated NaHCO3 solution (50 ml) twice, water (50 ml) and brine (40 ml) and
then dried over anhydrous MgSO4. The solution was concentrated in vacuo
and the resulting oil was dried at 60 °C in an oil bath with stirring in vacuo
to give ethyl (2S,3R)-2-hydroxy-3-(1H-indol-3-yl)butanoate ((ϩ)-2, 4.98 g,
quant.). 1H-NMR (CDCl3), d: 1.27 (3H, d, Jϭ7.4 Hz), 1.34 (3H, d, Jϭ
7.0 Hz), 2.75 (1H, d, Jϭ5.6 Hz), 3.63 (1H, dq, Jϭ3.2, 7.0 Hz), 4.25 (2H, q,
Jϭ7.4 Hz), 4.48 (1H, dd, Jϭ3.2, 5.6 Hz), 7.0—7.3 (3H, m), 7.37 (1H, d,
Jϭ7.0 Hz), 7.68 (1H, d, Jϭ7.4 Hz), 8.05 (1H, br s). IR (KBr, cmϪ1): 3400,
3337, 1728, 1456. Anal. Calcd for C14H17NO3: C, 68.00; H, 6.93; N, 5.66.
Found: C, 67.79; H, 7.21; N, 5.56. [a]D24 ϩ5.2° (cϭ1.11, methanol).
(5S)-2-Amino-5-[(1R)-1-(1H-indol-3-yl)ethyl]-2-oxazolin-4-one ((؊)-5)
To a solution of guanidine hydrochloride (9.56 g, 100 mmol) in tert-butanol
Chart 6
Chart 7
tive of 1, which was prepared by applying our synthetic route
for 1 to 6-benzyloxyindole 8,7) as shown in Chart 5. The sul-
fate of M-I was prepared by treatment of M-I with pyridine
sulfur trioxide complex (Chart 6) and the glucuronide of
M-I was obtained by treatment of M-I with the imidate 118)
in the presence of trimethylsilyl trifluoromethanesulfonate
(TMSOTf) followed by hydrolysis (Chart 7). The N-
demethylated metabolite M-II was the intermediate (Ϫ)-5 of
our synthesis of indolmycin 1. M-III was obtained by acety-
lation of the methylamino group of 1 followed by treatment
with hydrochloric acid (Chart 8). The structure of metabo-
lites M-I, M-II, M-III, M-I-Gluc, and M-I-SO3H were con-
firmed by comparison of the mass spectra and the HPLC re-
tention time with the synthetic compounds.
In conclusion, we have established a stereoselective practi-
cal synthetic route to indolmycin 1, a candidate anti-H. pylori
agent. This study has opened the way to synthesize 1 on a (40 ml) were added potassium tert-butoxide (11.2 g, 99.8 mmol) and molecu-

December 2001
1607
lar sieves 4A (10 g). The mixture was stirred for 3 d at room temperature and ethyl]-2-oxazolin-4-one (10, 2.27 g, 6.45 mmol) was dissolved into 40%
ethyl (2S,3R)-2-hydroxy-3-(1H-indol-3-yl)butanoate ((ϩ)-2, 4.98 g, 20.1 methylamine in methanol and allowed to stand for 8 h at 5 °C. The reaction
mmol) in tert-butanol (30 ml) was added. After stirring for 7.5 h at room mixture was concentrated to half volume under reduced pressure without
temperature, the reaction mixture was poured into ice cold saturated ammo- heating, water was added to the residue and then extracted with ethyl ac-
nium chloride (400 ml). After filtering, the filtrate was extracted with ethyl etate–tetrahydrofuran (5 : 1) twice. The combined organic layer was dried
acetate–isopropanol (250 ml, 4 : 1). The organic layer was washed with aque- over anhydrous MgSO4 and evaporated under reduced pressure. The residue
ous 5% NaHCO3 solution (100 ml) and water and then dried over anhydrous was dissolved into ethanol–tetrahydrofuran (7 : 3, 100 ml) and the solution
MgSO4. After evaporation, the residue was dissolved in hot ethyl acetate was stirred for 14 h at room temperature with 10% Pd/C (1.10 g) under H2
(23 ml) and allowed to stand. The resulting crystals were collected by filtra- atmosphere. The reaction mixture was filtered and evaporated under reduced
tion and washed with ethyl acetate (4 ml) to give (5S)-2-amino-5-[(1R)-1- pressure. Purification by column chromatography with silica gel (60 g,
(1H-indol-3-yl)ethyl]-2-oxazolin-4-one ((Ϫ)-5, 3.26 g, 67%). 1H-NMR hexane : acetoneϭ1 : 2) and MCI gel HP-20 (acetonitrile : waterϭ1 : 3) fol-
(DMSO-d6) d: 1.20 (3H, d, Jϭ7.4 Hz), 3.57 (1H, dq, Jϭ2.6, 7.4 Hz), 4.91
(1H, d, Jϭ2.6 Hz), 6.94—7.16 (3H, m), 7.35 (1H, d, Jϭ7.2 Hz), 7.58 (1H, d,
Jϭ7.4 Hz), 8.25 (1H, br s), 8.41 (1H, br s). IR (KBr, cmϪ1): 3588, 3261,
1724, 1638, 1541. Anal. Calcd for C13H13N3O2: C, 59.76; H, 5.79; N, 16.08.
Found: C, 59.65; H, 5.68; N, 16.07. [a]D22 Ϫ174.0° (cϭ2.0, methanol). mp
180.5—181.5 °C.
lowed by crystallization from acetonitrile–water (1 : 3) gave white crystals of
(5S)-5-[(1R)-1-(6-hydroxy-1H-indol-3-yl)ethyl]-2-methylamino-2-oxazolin-
4-one (M-I, 250 mg, 16%). 1H-NMR (DMSO-d6) d: 1.14 (2H, d, Jϭ7.2 Hz),
1.20 (1H, d, Jϭ7.0 Hz), 2.78 (1/3H, s), 2.80 (2/3H, s), 3.50 (1H, m), 4.87
(1/3H, d, Jϭ2.6 Hz), 4.90 (2/3H, d, Jϭ2.2 Hz), 6.52 (1H, dd, Jϭ1.8, 8.4 Hz),
6.70 (1H, d, Jϭ1.8 Hz), 6.91 (2/3H, br s), 6.94 (1/3H, br s), 7.33 (1H, d,
Jϭ8.4 Hz), 8.63 (1/3H, br s), 8.69 (2/3H, br s), 8.89 (1H, br s). IR (KBr,
cmϪ1): 3320, 3202, 1723, 1624. Anal. Calcd for C14H15N3O3 1.0H2O: C,
(5S)-5-[(1R)-1-(1H-Indol-3-yl)ethyl]-2-methylamino-2-oxazolin-4-one
(Indolmycin 1) (5S)-2-Amino-5-[(1R)-1-(1H-indol-3-yl)ethyl]-2-oxazolin-
4-one ((Ϫ)-5, 3.10 g, 12.7 mmol) was dissolved into 40% methylamine in 57.72; H, 5.88; N, 14.42. Found: C, 57.48; H, 5.76; N, 14.14. [a]D22 Ϫ185.2°
water (20 ml). The solution was allowed to stand in a refrigerator for 5 h at (cϭ0.1, methanol). mp 148—149 °C.
5 °C. The reaction mixture was concentrated to half volume under reduced
Sodium 3-{(1R)-1-[(5S)-2-Methylamino-4-oxo-4,5-dihydro-1,3-oxazol-
pressure without heating. The resulting crystals were collected by filtration 5-yl]ethyl}-1H-indol-6-yl Sulfate (M-I-SO3Na) To a solution of (5S)-5-
and recrystallized from methanol–water (6 ml, 2 : 1). The white crystals were [(1R)-1-(6-hydroxy-1H-indol-3-yl)ethyl]-2-methylamino-2-oxazolin-4-one
collected by filtration and dried to give (5S)-5-[(1R)-1-(1H-indol-3-yl)ethyl]- (M-I, 635 mg, 2.32 mmol) in N,N-dimethylformamide (DMF)–pyridine
2-methylamino-2-oxazolin-4-one (indolmycin 1, 2.10 g, 64%). 1H-NMR (4 : 1, 13 ml) was added pyridine–SO3 complex (2.00 g, 12.6 mmol) and the
(DMSO-d6) d: 1.19, 1.25 (3H, d, Jϭ7.0 Hz), 2.70—2.82 (3H, m), 3.59 (1H,
m), 4.90, 4.94 (1H, d, Jϭ2.4 Hz), 6.95—7.19 (3H, m), 7.35 (1H, d, at 0 °C and concentrated in vacuo. The reaction mixture was purified by col-
Jϭ7.8 Hz), 7.58 (1H, d, Jϭ7.8 Hz), 8.30 (1H, s), 8.64 (1H, br s), 10.93 (1H, umn chromatography with adsorbent resin (Sepabeads SP-207, water :
br s). IR (KBr, cmϪ1): 3266, 1730, 1604. Anal. Calcd for C14H15N3O2: C, acetonitrileϭ25 : 1) and preparative HPLC (YMC ODS-A, 250 mmϫ20 mm,
65.35; H, 5.88; N, 16.33. Found: C, 65.28; H, 5.73; N, 16.06. [a]D22 Ϫ212.5°
water : acetonitrileϭ97 : 3). After evaporation under reduced pressure, the
mixture was stirred for 60 h at room temperature. Water (15 ml) was added
(cϭ2.0, methanol) [lit.1a) [a]D25 Ϫ214° (cϭ2.0, methanol)]. mp 206—207 °C residue was dissolved in methanol and filtered. Concentration of the filtrate
(lit.1a) 209—210 °C).
Ethyl (2S,3R)-3-[6-(Benzyloxy)-1H-indol-3-yl]-2-hydroxybutanoate (9)
To a solution of methyl magnesium bromide in ethyl ether (2.93 M, 74 ml)
in vacuo gave a syrup which was powdered by treatment with ethyl acetate.
The powder was dissolved into methanol (10 ml) and 1 N NaOH (1.5 ml) was
added at 0 °C. After removal of the solvent, the mixture was purified by col-
was added 6-benzyloxyindole (8, 19.4 g, 86.9 mmol) in 190 ml of umn chromatography with Sephadex LH-20 (water). After evaporation
dichloromethane dropwise for 45 min under N2 atmosphere at 0 °C. After under reduced pressure, the residue was dissolved into water (9 ml) and
stirring for 30 min, the solution was cooled to Ϫ20 °C and then ethyl lyophilized to give sodium 3-{(1R)-1-[(5S)-2-methylamino-4-oxo-4,5-dihy-
(2S,3R)-2,3-epoxybutanoate ((ϩ)-3, 22.6 g, 174 mmol) in dichloromethane
(200 ml) was added dropwise for 3 h at Ϫ20 °C. After stirring for 1 h, 1 N
HCl (300 ml) was added. The organic layer was separated and the aqueous 2.83 (2H, s), 2.84 (1H, s), 3.64—3.82 (1H, m), 5.00 (2/3H, d, Jϭ2.6 Hz),
layer was extracted with dichloromethane (300 ml) twice. The combined or- 5.05 (1/3H, d, Jϭ3.0 Hz), 7.01 (1/3H, d, Jϭ8.7 Hz), 7.02 (2/3H, d, Jϭ
dro-1,3-oxazol-5-yl]ethyl}-1H-indol-6-yl sulfate (M-I-SO3Na, 332 mg, 63%).
1H-NMR (DMSO-d6) d: 1.35 (2H, d, Jϭ7.2 Hz), 1.40 (1H, d, Jϭ7.2 Hz),
ganic layer was dried over anhydrous MgSO4 and concentrated in vacuo.
8.7 Hz), 7.10 (2/3H, s), 7.13 (1/3H, br s), 7.33 (1/3H, s), 7.34 (2/3H, s), 7.54
The residue was purified by silica gel column chromatography (hexane– (2/3H, d, Jϭ8.7 Hz), 7.56 (1/3H, d, Jϭ8.7Hz). IR (KBr, cmϪ1): 3304, 1730,
ethyl acetate) to give ethyl (2S,3R)-3-[6-(benzyloxy)-1H-indol-3-yl]-2-hy- 1628, 1493. Anal. Calcd for C14H14N3O6SNa 1.5H2O: C, 41.79; H, 4.26; N,
1
droxybutanoate (9, 18.1 g, 59%). H-NMR (CDCl3) d: 1.27 (3H, d, Jϭ7.2 10.44. Found: C, 41.84; H, 4.22; N, 10.41. [a]D25 Ϫ139.6° (cϭ0.1, H2O).
Hz), 1.32 (3H, d, Jϭ7.2 Hz), 2.74 (1H, d, Jϭ5.6 Hz), 3.57 (1H, dq, Jϭ3.2,
7.2 Hz), 4.24 (2H, q, Jϭ7.2 Hz), 4.46 (1H, dd, Jϭ3.2, 5.6 Hz), 5.10 (2H, s),
Methyl (2S,3S,4S,5R,6S)-3,4,5-Tris(acetoxy)-6-[(3-{(1R)-1-[(5S)-2-
(methylamino)-4-oxo-4,5-dihydro-1,3-oxazol-5-yl]ethyl}-1H-indol-6-
6.85—6.90 (2H, m), 7.01 (1H, m), 7.23—7.57 (6H, m), 7.91 (1H, br s). IR yl)oxy]tetrahydro-2H-pyran-2-carboxylate (12) A suspension of (5S)-5-
(KBr, cmϪ1): 3364, 1732, 1628. Anal. Calcd for C21H23NO4 0.1H2O: C, [(1R)-1-(6-hydroxy-1H-indol-3-yl)ethyl]-2-methylamino-2-oxazolin-4-one
71.01; H, 6.58; N, 3.94. Found: C, 70.87; H, 6.75; N, 3.73. [a]D25 ϩ6.3° (M-I, 250 mg, 0.915 mmol) in dichloromethane (8 ml) was cooled at Ϫ15 °C
(cϭ0.104, methanol).
in an acetone–ice bath. TMSOTf (0.180 ml, 0.931 mmol) was added and the
mixture was stirred for 30 min at Ϫ15 °C under argon atmosphere. A solu-
tion of methyl 2,3,4-tri-O-acetyl-1-O-(trichloroacetimidoyl)-a-D-glucopyra-
nuronate (11, 715 mg, 1.49 mmol) in dichloromethane (2 ml) was added and
(5S)-2-Amino-5-[(1R)-1-(6-benzyloxy-1H-indol-3-yl)ethyl]-2-oxazolin-
4-one (10) To a solution of guanidine hydrochloride (17.6 g, 184 mmol) in
tert-butanol (180 ml) were added potassium tert-butoxide (20.7 g, 184 mmol)
and molecular sieves 4A (10 g). The mixture was stirred for 1 d at room tem- stirred for 2.5 h at Ϫ15 °C. Ethyl acetate (50 ml) was added to the reaction
perature and ethyl (2S,3R)-3-[6-(benzyloxy)-(1H-indol-3-yl)]-2-hydroxybu-
tanoate (9, 12.9 g, 36.5 mmol) in tert-butanol (120 ml) was added. After stir-
mixture and washed with 0.1 N HCl, saturated aqueous NaHCO3 solution
and brine and then dried over MgSO4. After removal of the solvent, the
ring for 20 h at room temperature, the reaction mixture was poured into ice- residue was purified by silica gel column chromatography (20 g,
saturated ammonium chloride (600 ml). After filtering, the filtrate was ex- CH2Cl2 : methanolϭ90 : 10) to give methyl (2S,3S,4S,5R,6S)-3,4,5-tris(ace-
tracted with ethyl acetate–ethanol (400 ml, 7 : 1) twice. The organic layer toxy)-6-[(3-{(1R)-1-[(5S)-2-(methylamino)-4-oxo-4,5-dihydro-1,3-oxazol-5-
was washed with aqueous saturated NaHCO3 solution and dried over anhy- yl]ethyl}-1H-indol-6-yl)oxy]tetrahydro-2H-pyran-2-carboxylate
(12,
drous MgSO4. After evaporation, the residue was dissolved in hot ethyl ac- 145 mg, 27%). 1H-NMR (CDCl3) d: 1.34 (1.5H, d, Jϭ7.0 Hz), 1.44 (1.5H, d,
etate (75 ml) and allowed to stand. The resulting crystals were collected by Jϭ7.4 Hz), 2.05—2.09 (9H, m), 2.84 (1.5H, s), 2.95 (1.5H, d, Jϭ4.8 Hz),
filtration and washed with ethyl acetate to give (5S)-2-amino-5-[(1R)-1-(6- 3.66 (1.5H, s), 3.73 (1.5H, s), 3.79 (1H, m), 4.22 (1H, d, Jϭ9.6 Hz), 4.87,
benzyloxy-1H-indol-3-yl)ethyl]-2-oxazolin-4-one (10, 8.62 g, 68%). 1H-NMR
(DMSO-d6) d: 1.18 (3H, m), 3.51 (1H, m), 4.89 (1H, d, Jϭ2.4 Hz), 5.11
4.90 (1H, d, Jϭ2.6 Hz), 5.13 (1H, dd, Jϭ5.4, 7.4 Hz), 5.20—5.40 (1H ,m),
6.80 (1H, dd, Jϭ2.2, 8.4 Hz), 7.03—7.07 (2H, m), 7.51 (0.5H, d, Jϭ8.4 Hz),
(2H, s), 6.74 (1H, dd, Jϭ2.2, 8.6 Hz), 6.93—7.03 (3H, m), 7.31—7.49 (5H, 7.52 (0.5H, d, Jϭ8.8 Hz), 8.37 (1H, m). IR (KBr, cmϪ1): 3198, 1759, 1622,
m), 8.30 (2H, br s), 10.73 (1H, br s). IR (KBr, cmϪ1): 3317, 1738, 1658, 1221. Anal. Calcd for C27H31N3O12 1.5H2O: C, 52.60; H, 5.56; N, 6.82.
1556. Anal. Calcd for C20H19N3O3: C, 67.03; H, 5.62; N, 11.72. Found: C, Found: C, 52.74; H, 5.43; N, 6.54. [a]D24 Ϫ103.1° (cϭ0.22, methanol).
67.22; H, 5.53; N, 11.49. [a]D24 Ϫ121.5° (cϭ0.2, methanol). mp 217—
Sodium (2S,3S,4S,5R,6S)-3,4,5-Trihydroxy-6-[(3-{(1R)-1-[(5S)-2-(methy-
lamino)-4-oxo-4,5-dihydro-1,3-oxazol-5-yl]ethyl}-1H-indol-6-yl)oxy]-
218 °C.
(5S)-5-[(1R)-1-(6-Hydroxy-1H-indol-3-yl)ethyl]-2-methylamino-2-oxa- tetrahydro-2H-pyran-2-carboxylate (M-I-GlucNa) To
a solution of
zolin-4-one (M-I) (5S)-2-Amino-5-[(1R)-1-(6-benzyloxy-1H-indol-3-yl)- methyl (2S,3S,4S,5R,6S)-3,4,5-tris(acetoxy)-6-[(3-{(1R)-1-[(5S)-2-(methyl-

1608
Vol. 49, No. 12
amino)-4-oxo-4,5-dihydro-1,3-oxazol-5-yl]ethyl}-1H-indol-6-yl)oxy]-
tetrahydro-2H-pyran-2-carboxylate (12, 400 mg, 0.678 mmol) in methanol
(14 ml) was added sodium carbonate (198 mg, 1.87 mmol) in water (6 ml) at
0 °C. After stirring for 3.5 h at 0 °C, the solution was adjusted to pH 5 with
1 N HCl and concentrated under reduced pressure. The residue was purified
by preparative HPLC (YMC ODS-A, 250 mmϫ20 mm, water : acetoni-
trileϭ97 : 3) followed by lyophilization to give sodium (2S,3S,4S,5R,6S)-
3,4,5-trihydroxy-6-[(3-{(1R)-1-[(5S)-2-(methylamino)-4-oxo-4,5-dihydro-
1,3-oxazol-5-yl]ethyl}-1H-indol-6-yl)oxy]tetrahydro-2H-pyran-2-carboxy-
(1H, d, Jϭ3.2 Hz), 6.95—7.13 (2H, m), 7.18 (1H, d, Jϭ2.4 Hz), 7.36 (1H, d,
Jϭ7.4 Hz), 7.57 (1H, d, Jϭ7.6 Hz), 10.98 (1H, br s), 11.76 (1H, br s). IR
(KBr, cmϪ1): 3393, 3258, 1815, 1746, 1460. Anal. Calcd for C13H12N2O3: C,
63.93; H, 4.95; N, 11.47. Found: C, 63.89; H, 4.85; N, 11.50. [a]D22 Ϫ180.8°
(cϭ1.08, methanol). mp 179—179.5 °C.
References
1) a) Rao K. V., Antibiot. Chemother., 10, 312—315 (1960); b) Schach
von Wittenau M., Els H., J. Am. Chem. Soc., 83, 4678—4680 (1961);
c) Chan T. H., Hill R. K., J. Org. Chem., 35, 3519—3521 (1970).
2) Marsh W. S., Garretson A. L., Wesel E. M., Antibiot. Chemother., 10,
316—320 (1960).
3) Kanamaru T., Nakano Y., Toyoda Y., Miyagawa K., Tada M., Kaisho
T., Nakao M., Antimicrob. Agents Chemother., 45, 2455—2459
(2001).
4) a) Preobrazhenskaya M. N., Balashova E. G., Turchin K. F.,
Padeiskaya E. N., Yvarova N. V., Pershin G. N., Suvorov M. N., Tetra-
hedron, 24, 6131—6143 (1968); b) Takeda T., Mukaiyama T., Chem.
Lett., 1980, 163—166; c) Dirlam J. P., Clark D. A., Hecker S. J., J.
Org. Chem., 51, 4920—4924 (1986); d) Shue Y.-K., Tetrahedron Lett.,
37, 6447—6448 (1996); e) Schach von Wittenau M., Els H., J. Am.
Chem. Soc., 85, 3425—3431 (1963).
5) Bader H., Oroshnik W., J. Am. Chem. Soc., 81, 163—167 (1959).
6) a) Sharpless K. B., Ambergm W., Bennani Y. L., Crispino G. A., Har-
tung J., Jeong K.-S., Kwong H.-L., Morikawa K., Wang Z.-M., Xu D.,
Zhang X.-L., J. Org. Chem., 57, 2768—2771 (1992); b) Fleming P. R.,
Sharpless K. B., ibid., 56, 2869—2875 (1991); c) Genet J.-P., Cano
Andrade M. C., Ratovelomanana-Vidal V., Tetrahedron Lett., 36,
2063—2066 (1995); d) Akita H., Kawaguchi T., Enoki Y., Oishi T.,
Chem. Pharm. Bull., 38, 323—328 (1990).
1
late (M-I-GlucNa, 93 mg, 31%). H-NMR (DMSO-d6) d: 1.17, 1.26 (3H, d,
Jϭ7.0 Hz), 2.76—2.81 (3H, m), 3.60—6.80 (5H, m), 4.74 (1H, dd, Jϭ2.6,
6.8 Hz), 4.87, 4.92 (1H, d, Jϭ2.6 Hz), 4.99 (1H, br s), 5.23 (1H, br s), 6.80
(1H, m), 7.05 (2H, m), 7.46 (1H, d, Jϭ8.4 Hz), 10.78 (1H, br s). IR (KBr,
cmϪ1): 3300, 3192, 1730, 1626, 1413. Anal. Calcd for C20H22N3O9Na
2.5H2O: C, 46.51; H, 5.27; N, 8.14. Found: C, 46.56; H, 5.19; N, 8.24. [a]D25
Ϫ219.3° (cϭ0.01, H2O).
(5S)-5-[(1R)-1-(1H-Indol-3-yl)ethyl]-1,3-oxazolidine-2,4-dione (M-III)
To a solution of (5S)-5-[(1R)-1-(1H-indol-3-yl)ethyl]-2-methylamino-2-oxa-
zolin-4-one (indolmycin 1, 5.00 g, 19.4 mmol) in tetrahydrofuran (THF)
(65 ml) were added at 0 °C triethylamine (8.13 ml, 58.3 mmol) and acetic an-
hydride (3.66 ml, 38.8 mmol). The mixture was stirred for 30 min at 0 °C and
then for 5 h at room temperature. After addition of ethyl acetate (520 ml) and
water (130 ml) at 0 °C, the reaction mixture was stirred for 30 min. The ethyl
acetate layer was separated, washed with brine (130 ml) and dried over anhy-
drous MgSO4. After concentration under reduced pressure, the residue was
crystallized from isopropyl ether and the crystals were collected by filtration.
To a solution of the crystals in acetonitrile (100 ml) was added 1 N HCl
(40 ml) and stirred for 110 min at room temperature. After removal of the
solvent by concentration, water (100 ml) was added and the aqueous layer
was extracted with ethyl acetate (250 ml). The ethyl acetate layer was
washed with water (50 ml) an brine (50 ml) and dried over anhydrous
MgSO4. After concentration in vacuo, the residue was crystallized from iso-
propyl ether–hexane. Recrystallization from methanol–water afforded (5S)-
5-[(1R)-1-(1H-indol-3-yl)ethyl]-1,3-oxazolidine-2,4-dione (M-III, 2.25 g,
7) Teranishi K., Nakatsuka S., Goto T., Synthesis, 1984, 1018—1020.
8) a) Bollenback G. N., Long J. W., Benjamin D. G., Lindquist J. A., J.
Am. Chem. Soc., 77, 3310—3315 (1955); b) Nudelman A., Herzig J.,
Gottlieb H. E., Carbohydr. Res., 162, 145—152 (1987); c) Schmitt R.
R., Grundler G., Synthesis, 1981, 885—887.
1
47%). H-NMR (DMSO-d6) d: 1.36 (3H, d, Jϭ7.2 Hz), 3.67 (1H, m), 5.20