Novel synthesis of the main central 2,3,6-trisubstituted pyridine skeleton [Fragment A-B-C] of a macrobicyclic antibiotic, cyclothiazomycin

Article abstract of DOI:10.1246/bcsj.75.1583

The useful synthesis of the main central 2,3,6-trisubstituted pyridine skeleton [the protected Fragment A-B-C] of a macrobicyclic antibiotic, cyclothiazomycin, was first accomplished. First, the 2-[2-(2-substituted thiazol-4-yl)]-4,5-dihydrothiazole-4-carboxylate [Fragment A derivative], attached to the 6-substituent of the main pyridine skeleton, was synthesized by two consecutive thiazolations of the protected Ser thioamide derivative with 3-bromopyruvate, and then thiazolination of the C-terminal Ser residue of the sequence. Secondly, an efficient synthesis of the central 2-(2-{2[(1R)-1-aminoethyl]pyridin-6-yl}thiazol-4-yl)-4, 5-dihydrothiazole-4-carboxylate [Fragment B derivative] was also achieved by thiazolation of the formyl group of the 2-(1-aminoethyl)-6-formylpyridine derivative, and then thiazolination. Thirdly, a convenient synthesis of the protected dehydrotetrapeptide [Fragment C derivative], which is bound to the 2-substituent of the pyridine skeleton, was attained by the usual stepwise elongation of the appropriate α-amino acids and β-elimination of a Thr residue of the sequence. Finally, the facile fragment condensation of the three Fragments thus obtained gave the protected Fragment A-B-C derivative via Fragment A-B. Furthermore, the configurational structures of the three Fragments (A, B, and C) were also investigated.

Full text of DOI:10.1246/bcsj.75.1583

Bull. Chem.
Soc. Jpn.
75
7
© 2002 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 75, 1583–1596 (2002) 1583
The Chemical
Society of Ja-
pan
The Chemical
Society of Ja-
pan
OB
7
15
Novel Synthesis of the Main Central 2,3,6-Trisubstituted Pyridine
Skeleton [Fragment A-B-C] of a Macrobicyclic Antibiotic,
Cyclothiazomycin
Main Structure of Cyclothiazomycin
C. Shin et al.
2002
1583
1596
BCSJA8
0009-2673
01450
12
Chung-gi Shin,* Akihiro Okabe, Akinori Ito, Akio Ito, and Yasuchika Yonezawa
Laboratory of Organic Chemistry, Faculty of Engineering, Kanagawa University,
Rokkakubashi, Kanagawa-ku, Yokohama 221-8686
(Received December 21, 2001)
21
2001
3
19
The useful synthesis of the main central 2,3,6-trisubstituted pyridine skeleton [the protected Fragment A-B-C] of a
macrobicyclic antibiotic, cyclothiazomycin, was first accomplished. First, the 2-[2-(2-substituted thiazol-4-yl)]-4,5-di-
hydrothiazole-4-carboxylate [Fragment A derivative], attached to the 6-substituent of the main pyridine skeleton, was
synthesized by two consecutive thiazolations of the protected Ser thioamide derivative with 3-bromopyruvate, and then
thiazolination of the C-terminal Ser residue of the sequence. Secondly, an efficient synthesis of the central 2-(2-{2-
[(1R)-1-aminoethyl]pyridin-6-yl}thiazol-4-yl)-4,5-dihydrothiazole-4-carboxylate [Fragment B derivative] was also
achieved by thiazolation of the formyl group of the 2-(1-aminoethyl)-6-formylpyridine derivative, and then thiazolina-
tion. Thirdly, a convenient synthesis of the protected dehydrotetrapeptide [Fragment C derivative], which is bound to the
2-substituent of the pyridine skeleton, was attained by the usual stepwise elongation of the appropriate α-amino acids
and β-elimination of a Thr residue of the sequence. Finally, the facile fragment condensation of the three Fragments thus
obtained gave the protected Fragment A-B-C derivative via Fragment A-B. Furthermore, the configurational structures
of the three Fragments (A, B, and C) were also investigated.
2002
4.4.2
4.9.4
Cyclothiazomycin (1),1 isolated from a culture of Strepto-
myces NR0516, is a very interesting thiostrepton-type macrobi-
cyclic antibiotic. So far, many structurally similar thiostrepton
antibiotics, such as GE 2270 A,2 micrococcins P and P1,3 have
also been isolated from various kinds of strains. However, no
total synthesis of any similar antibiotic has yet been reported,
except for the recent syntheses of micrococcin P and P1.4–6
The cyclothiazomycin features a very unique structure and in-
teresting bioactivities,1 which attracted our attention and
prompted us to investigate its total synthesis and structure-bio-
activity relationship. The natural product 1 includes a charac-
teristic main central and long chain 2,3,6-trisubstituted pyri-
dine skeleton, called Fragment A-B-C 2, which is constituted
of an (S)-2-{2-[2-(1-aminoethenyl)thiazol-4-yl]thiazol-4-
yl}thiazoline-4-carboxylate segment called Fragment A 4, a
central (4S)-2-(2-{2-[(1R)-1-aminoethyl]-3-carboxypyridin-6-
yl}thiazol-4-yl)-4,5-dihydrothiazole-4-carboxylate skeleton,
called Fragment B 5, and L-Thr-Gly-(Z)-∆Abu-L-Pro (∆Abu =
2-amino-2-butenoic acid residue) sequence, called Fragment C
6, as shown in Fig. 1. Moreover, interestingly, many 4,5-dihy-
drothiazole-4-carboxylate moieties, which are unusual in
thiostrepton-type antibiotics, are involved.
Fig. 1. Retrosynthesis of 1.

1584 Bull. Chem. Soc. Jpn., 75, No. 7 (2002)
Main Structure of Cyclothiazomycin
In connection with the total synthesis of 1, we have already
briefly reported a novel synthesis of the protected Fragment A
derivative (P)-47 by two consecutive thiazolations, and then
thiazolination of the protected Ser thioamide derivative with 3-
bromopyruvate by the Hantzsch method.8 More recently,9 a
useful synthesis of the protected Fragment B derivative (P)-5
by successive thiazolination and thiazolation of a 2,3-disubsti-
tuted 6-formylpyridine derivative10 with H-Cys-OMe was
achived by the Shioiri method.11 Furthermore, the facile syn-
thesis of the protected Fragment A-B drivative (P)-3 by the
coupling of Fragment A with Fragment B, mentioned above,
has also been briefly reported.9
In this paper, we wish to report in detail on versatile synthet-
ic methods for all of the Fragment derivatives [(P)-4, 5, and 6],
the protected Fragment [A-B (P)-3], and Fragment A-B-C de-
rivatives [(P)-2], derived by coupling of (P)-3 with (P)-6. Fur-
thermore, in order to determine which of the two synthetic ste-
reoisomers, 2-(1ꢀR)- and 2-(1ꢀS)-(P)-5, is identical to the con-
figuration of natural 1, the structures of the two isomers were
thoroughly examined by comparing the circular dichroism
(CD) spectra and the specific rotations ([α]D) with those of an
independently prepared structurally similar 2-(1-aminoeth-
yl)pyridine derivative.
corresponding thiocarbonyl-Ser-OMe derivative 16, which was
treated with triphenylphosphine (Ph3P) and diethyl azodicar-
boxylate (DEAD) by the Mitsunobu reaction13 to give the ex-
pected 2-(2,4ꢀ-bithiazol-4-yl)-4,5-dihydrothiazole-4-carboxy-
late 17.
Finally, deprotection of only the isopropylidene (Isop)
group of the 2,2-dimethyloxazolidine ring with a mixture of
trifluoroacetic acid (TFA) and CHCl3 (4:96 v/v) gave the cor-
responding 2-[2ꢀ-(1-amino-2-hydroxyethyl)-2,4ꢀ-bithiazol-4-
yl]-4,5-dihydrothiazole derivative 18. Subsequent protection
of the formed hydroxy group of 18 with t-butyldiphenylsilyl
chloride (TPS-Cl) in the presence of imidazole gave the corre-
sponding 2-(O-TPS)ethyl derivative 19 as the protected Frag-
ment A derivative, as shown in Scheme 1. As a result, a conve-
nient synthesis of 19 was achieved by two consecutive thiaz-
olations and thiazolination from 7; the overall yield was found
to attain to 19% from Ser. Later, after deprotection of the Boc
group of 19 with TFA, without isolation, the obtained amino
group free amino-2-(2,4ꢀ-bithiazol-4-yl)-4,5-dihydrothiazole
derivative (P)-4 was intact utilized to the next coupling with
(P)-5.
The structure of 19 was determined by the 1H NMR spectral
data and satisfactory elemental analysis. In particular, the ap-
pearances of two protons of the thiazole rings as a singlet at δ
8.03 and 8.04, the methylene protons as a double doublet at δ
3.68 (J = 5.8 and 9.2 Hz) and the methine proton of thiazoline
(4,5-dihydrothiazole) ring as a triplet at δ 5.32 supported the
formation of 19.
Results and Discussion
The novel syntheses of the protected Fragment A, B, and C
derivatives and their couplings for the formations of the pro-
tected Fragments A-B and A-B-C derivatives were accom-
plished as follows. In particular, with regard to the synthesis
of the Fragment A (P)-4, since the previous synthetic method7
was found to be slightly difficult, and the overall yield from
Ser is very low (2%), an alternative revised method was adopt-
ed. First of all, to synthesize the protected 3,4-bithiazolyl-
thiocarbonyl-Ser-OMe derivative 16 as the precursor of (P)-4,
the synthesis of the desired thiazolylthiazole sequence 13 by
the stepwise thiazolations of thioamides was successfully tried.
Initially, the thiazolation of the 3-t-butoxycarbonyl(Boc)-2,2-
dimethyloxazolidine-4-thiocarboxamide (7),4 derived from
Boc-L-Cys-OH and acetone, with ethyl 3-bromopyruvate in
the presence of KHCO3, and then with trifluoroacetic anhy-
dride (TFAA) and pyridine, proceeded to give 2-substituted
thiazole-4-carboxylate derivative 8 by the Hantzsch method.8
After ester hydrolysis with 1 M LiOH (1 M = 1 mol dm−3),
amidation of the formed free carboxylic acid 9 with ClCOOEt
and then a 28% NH3 aqueous solution gave the corresponding
thiazole-4-carboxamide derivative 10. Similarly to the case of
8, thioamidation with Lawesson's reagent, followed by thiaz-
olation of the formed thiazole-4-thioamide 11 with ethyl 3-
bromopyruvate, gave the corresponding 2-substituted 2-(thiaz-
ol-4-yl)thiazole-4-carboxylate derivative 12. The ester was
again hydrolyzed with 1 M LiOH to give the corresponding
free acid 13.
On the other hand, to synthesize the Fragment B derivative,
as was already reported,9 first, the starting 3-cyano-6-di-
methoxymethyl-2-pyridone (20)10 was converted to the corre-
sponding 2-oxo-1,2-dihydropyridine-3-carboxylic acid 21 by
hydrolysis of the cyano group with 6 M KOH. Without the
isolation of 21, one-pot esterification with MeOH gave the me-
thyl ester 22, the carbonyl group of which was then triflated
with trifluoromethanesulfonic (triflic) anhydride (Tf2O) to give
the corresponding 2-(trifluoromethylsulfonyloxy)pyridine de-
rivative 23. The 2-TfO group was then treated with ethyl vinyl
ether in the presence of Pd(OAc)2 and dppp [1,3-bis(diphen-
ylphosphino)propane] to give the 2-(1-ethoxyvinyl)pyridine
derivative 24. Without the purification of 24, the conversion of
the ethoxyvinyl group to an acetyl group by using 70% AcOH
afforded the corresponding 2-acetyl-3-methoxycarbonyl deriv-
ative 25, which was then subjected to reduction. That is, the
simultaneous reductions of both the acetyl and methoxycar-
bonyl groups with NaBH4 in the presence of CaCl2 gave the
(RS)-2-(1-hydroxyethyl)-3-(hydroxymethyl)pyridine deriva-
tive 26 as a racemate. Subsequently, the formed primary hy-
droxy group of 26 was protected by TPS-Cl to give the 3-(O-
TPS-hydroxymethyl)pyridine derivative 27, and the secondary
hydroxy group was mesylated with methanesulfonyl (mesyl)
chloride (Ms-Cl) in the presence of Et3N and then azidated
with NaN3 in one-pot to give the corresponding 2-(1-azidoeth-
yl)pyridine derivative 28. The hydrogenolysis of the azido
group with 10% Pd–C/H2 gave the 2-(1-aminoethyl)pyridine
derivative 29, the amino group of which was in situ protected
with Boc2O (di-t-butyl dicarbonate) to give the expected 6-
dimethoxymethyl-2-[1-(N-Boc)aminoethyl]pyridine derivative
30, as shown in Scheme 2.
Subsequently, the coupling of 13 with H-L-Ser(TBS)-OMe
(TBS = t-butyldimethylsilyl) by using DPPA (DPPA = diphen-
yl phosphorazidate)12 as the condensing agent, followed by
thioamidation of the formed peptide derivative 14 with
Lawesson’s reagent gave 2,4-bithiazole-4-thiocarbonyl-Ser-
(TBS)-OMe 15. Deprotection of the TBS group with TBAF
(tetrabutylammonium fluoride) was then performed to give the

C. Shin et al.
Bull. Chem. Soc. Jpn., 75, No. 7 (2002) 1585
Scheme 1. Reagents and conditions: i) a) KHCO3, ethyl 3-bromopyruvate, DME, 0 °C, 30 min, rt, 2 h, b) TFAA, pyridine, DME, 0
°C, 1 h, ii) 1 M LiOH, H2O–dioxane (1:1 v/v), 0 °C, 30 min, rt, 3 h, iii) a) ClCOOEt, Et3N, THF, 0 °C, 30 min, b) 28% aq NH3,
THF, 0 °C, 5 min, iv) Lawesson’s reagent, DME, rt, 10 h, v) H-Ser(TBS)-OMe, DPPA, Et3N, DMF, 0 °C, 30 min, rt, 9 h,
vi) Lawesson’s reagent, 50 °C 16 h, vii) TBAF, THF, 0 °C 1 h, viii) Ph3P, DEAD, THF, 0 °C, 1 h, ix) TFA–CHCl3 (4:96 v/v), rt, 2
h, x) TPSCl, imidazole, CHCl3, 0 °C, rt, 12 h, xi) THF–CHCl3 (2:3 v/v), rt, 30 min.
Scheme 2. Reagents and conditions: i) 6 M KOH, EtOH, reflux, 8 h, 0 °C, 30 min, rt, 2 h, ii) H+, MeOH, reflux, overnight, iii) Tf2O,
DMAP, pyridine, 0 °C, 30 min, iv) Pd(OAc)2, dppp, ethyl vinyl ether, v) 70% AcOH, THF, rt, overnight, vi) NaBH4, CaCl2, EtOH,
0 °C, 30 min, rt, 3 h, vii) TPS-Cl, Et3N, DMAP, CH2Cl2, 0 °C, 30 min, rt, 2 h, viii) a) MsCl, Et3N, CH2Cl2, 0 °C, 10 min, b) NaN3,
DMF, rt, 1 h, ix) H2, 10% Pd–C, EtOH, rt, 30 min, x) Boc2O, Et3N, CHCl3, 0 °C, 30 min, rt, 4 h.
Secondly, in order to construct the thiazolylthiazoline-4-car-
boxylate segment to the 6-position of the pyridine ring of 30,
in the first place, the 6-dimethoxymethyl group was hydro-
lyzed. That is, the hydrolysis of the 6-dimethoxymethyl group
with 2 M HCl, followed by one-pot thiazolation of the formed
6-formylpyridine derivative 31 with H-L-Cys-OMe and then
oxidation with MnO2,11 gave the 2-(pyridin-6-yl)thiazole-4-
carboxylate derivative 32. The subsequent ester hydrolysis of
32 with 1 M LiOH gave the free acid 33, without purification,
the carboxyl group of which was again esterified with phena-
cyl bromide (Pac-Br) to give the corresponding Pac ester 34.
On the other hand, deprotection of the 3-(O-TPS)hydroxy-
methyl group by using TBAF was followed by oxidation of the
formed 3-(hydroxymethyl)pyridine derivative 35 with Jones’
reagent. As a result, unexpectedly, the formed labile 2-[1-(N-
Boc)aminoethyl]pyridine-3-carboxylic acid was immediately
intramolecularly cyclized to give the corresponding γ-lactam
derivative 36. Fortunately, it was found that the formation of
the γ-lactam ring resulted in the effective protection of the 2
and 3-positions of 36. Consequently, after hydrolysis of the

1586 Bull. Chem. Soc. Jpn., 75, No. 7 (2002)
Main Structure of Cyclothiazomycin
Pac ester with K2CO3 aqueous solution, without isolation, the
formed free acid 37 was in situ coupled with H-L-Ser(TBS)-
OBut by the DPPA method to give the 2-(pyridin-6-yl)thiaz-
oloyl-Ser-OBut derivative 38 as a diastereomeric mixture. Fur-
thermore, the γ-lactam ring was easily clevaged with 1 M
LiOH to give the corresponding 3-carboxyl-pyridine derivative
39, which was utilized in the next reaction without isolation.
Later, to differentiate the carboxy (C-) terminal t-butyl ester
from another ester, the carboxyl group of 39 was esterified
with benzyl bromide (Bn-Br) to give the corresponding 3-ben-
zyl ester derivative 40. Similarly to the case of 15, the thioam-
idation of 40 with Lawesson’s reagent gave the expected thio-
carbonyl-Ser(TBS) derivative 41. Although compound 41
was obtained as a diastereomeric mixture, the separation was
tried very successfully. That is, after the deprotection of the
TBS group with 2 M HCl, the product was chromatographed
intact on a silica-gel column using a mixture of CHCl3 and ac-
etone (50:1 v/v) to give the corresponding 2-[(1R)- and (1S)-1-
aminoethyl]pyridine derivatives 42 from the last eluate and 43
from the first eluate, respectively.
thiazole ring protons at δ 8.20 as a singlet (1H), and the thiazo-
line ring protons at δ 3.63 as a doublet (2H, J = 9.2 Hz) and at
δ 5.22 as a triplet (1H, J = 9.2 Hz) definitely support the Frag-
ment B skeleton structure. Therefore, it could be completely
determined that the absolute structure of 44 was the (1ꢀR,4S)-
configuration and identical with that of the natural 1. As a re-
sult, the compound (P)-5 (44) was found to be first synthe-
sized.
In addition, to synthesize the protected Fragment C deriva-
tive (P)-6, the condensation of N-Boc-N,O-Isop-L-Thr-OH
(52) with H-Gly-OMe by the usual DCC and N-hydroxysuc-
cinimide (HOSu) method gave the corresponding dipeptide
methyl ester 53, the methyl ester of which was hydrolyzed
with 1 M LiOH to give the free carboxylic acid 54. Similarly,
compound 54 was elongated by coupling with H-L-Thr(TBS)-
OMe to give the protected tripeptide methyl ester 55, the TBS
group of which was then deprotected with TBAF to give the
protected L-Thr-Gly-L-Thr-OMe derivative 56. Subsequently,
to synthesize the expected ∆3-dehydrotripeptide,15 the β-elimi-
nation of 56 with successive Ms-Cl in the presence of Et3N and
with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) was per-
formed to give the protected ∆3-dehydrotripeptide derivative
(N-Boc-N,O-Isop-L-Thr-Gly-(Z)-∆Abu-OMe) 57, by a previ-
ously reported method.16 After ester hydrolysis with 1 M
LiOH, the obtained free acid 58 was further elongated with H-
L-Pro-OMe by the DCC method to give ∆3-dehydrotetrapep-
tide methyl ester 59, the methyl ester of which was finally hy-
drolyzed to give the corresponding hydrolyzate derivative (P)-
6 as the protected Fragment C, as shown in Scheme 5. The ge-
ometry of the ∆Abu residue was readily determined to be the
(Z)-configurational structure by a comparison with the exten-
sive 1H NMR data of the authentic samples previously reported
by us.17
Lastly, one of the diastereomers 42 was thiazolinated with
Mitsunobu reagent13 to give only the corresponding 2-[2-(pyri-
din-6-yl)thiazol-4-yl]-4,5-dihydrothiazole derivative 44. On
the other hand, in the case of another diastereomer 43, interest-
ingly, although similar thiazolination proceeded, it was found
that a mixture of the thiazolylthiazoline derivative 46 and thia-
zolylithiazole derivative 47 was obtained in 67% yield in a
1:2.5 ratio. The obtained mixture could be readily separated
by the chromatogram method on a silica-gel column using a
mixture of hexane and EtOAc (2:1 v/v). Subsequently, oxida-
tion of the thiazoline ring of 44 with MnO2 in toluene gave the
corresponding bithiazole derivatives 45, similar to 47, as
1
shown in Scheme 3. As a result, the physical (IR and H
NMR) and chemical constants (mp and elemental analysis) of
45 and 47 were found to be completely identical, but only the
sign of the specific rotations were reversed. These facts clearly
indicate that compounds 44 and 46 as well as 42 and 43 are di-
astereomers; further, 45 and 47 are enantiomers to each other.
Naturally, it is neccessary to examine which of the two con-
figurational structures of 44 and 46 is identical with that of the
natural product (1). Accordingly, in order to determine the
configuration of the 2-(1-aminoethyl) moiety of the synthetic
44 and 46, both (R)- and (S)-configurational 2-[1-(N-Boc)ami-
noethyl]pyridines (51) were independently synthesized, and
their CD spectra were compared with those of 44 and 46. That
is, the well-known asymmetric reduction of 2-acetylpyridine
(48) with Baker’s Yeast afforded the authentic (S)-2-(1-hy-
droxyethyl)pyridine 49,14 which was further converted to (R)-
51 via (R)-2-(1-azidoethyl)pyridine 50. The specific rotation
value of 49 thus obtained was [α]D26 −55.5° (c 1.6, EtOH)
{lit.14 [α]D −55.5° (c 1.5, EtOH)}, showing high optical purity
(96% ee). Similarly, (S)-51 was also obtained from (S)-49 via
successive (R)-49 and (S)-50, as shown in Scheme 4. More-
over, the CD spectra of optically active 44 and (R)-51 showed
strong negative Cotton effects at 373 and 270 nm, respectively,
while those of 46 and (S)-51 showed positive Cotton effects in
the same region. Furthermore, from the 1H NMR spectrum of
44, the appearances of the chemical shifts of the pyridine ring
protons at δ 8.17 and 8.34 as a doublet (2H, J = 8.3 Hz), the
Finally, the hydrolysis of the t-butyl ester of (1ꢀR,4S)-(P)-5
with a mixture of TFA and CHCl3 (3:2 v/v), accompanying
deprotection of the Boc group, gave the corresponding free in-
termediate of both the amino and carboxyl groups. The amino
group of the yielded intermediate was protected intact again
with Boc2O to give the corresponding N-Boc-4,5-dihydrothia-
zole-4-carboxylic acid derivative 60. Without isolating 60,
one-pot coupling with (P)-4 gave the protected Fragment A-B
derivative (P)-3, by the BOP method.18 Lastly, deprotection of
the Boc group of (P)-3 with a mixture of TFA and CHCl3 (2:3
v/v), followed by similar coupling with (P)-6 gave first the ex-
pected Fragment A-B-C (P)-2, as shown in Scheme 6.
The structures of all the thus-obtained new products were
confirmed by the spectral data (1H NMR , IR, and specific rota-
tion) and satisfactory elemental analyses.
In conclusion, a useful synthetic method for the main cen-
tral Fragment A-B-C skeleton of cyclothiazomycin (1) was
successfully developed. A further investigation of the total
synthesis of 1 is currently under way in our laboratory.
Experimental
The melting points were measured using a Yamato (Model Mp-
21) micro-melting point apparatus, and are uncorrected. The IR
spectra were recorded using an EPI-G2 spectrometer in KBr. The
1H NMR spectra were measured with JEOL EX 90, EX 200, and
JNE 500 spectrometers in CDCl3 or DMSO-d6 solution with tet-

C. Shin et al.
Bull. Chem. Soc. Jpn., 75, No. 7 (2002) 1587
Scheme 3. Reagents and conditions: i) 2 M HCl, rt, overnight, ii) a) HCl•H-L-Cys-OMe, Et3N, toluene, rt, 10 h, b) MnO2 , toluene,
rt, overnight, iii) 1 M LiOH, H2O–dioxane (1:1 v/v), 0 °C, 30 min, rt, 8 h, iv) PacBr, Et3N, DMF, 0 °C, 30 min, rt, 6 h, v) TBAF,
THF, 0 °C, 30 min, vi) Jones reagent, acetone, 0 °C, 30 min, vii) K2CO3, THF, H2O, 0 °C, 30 min, rt, 8 h, viii) H-L-Ser(TBS)-
OBut, DPPA, Et3N, DMF, 0 °C, 30 min, rt, overnight, ix) 1 M LiOH, THF, H2O, 0 °C, 30 min, rt, 1 h, x) BnBr, Et3N, DMF, 0 °C,
30 min, rt, 12 h. xi) Lawesson’s, reagent, DMF, 50 °C, 12 h, xii) 2 M HCl, THF, rt, xiii) Ph3P, EDAD, THF, 0 °C, 30 min,
xiv) MnO2, toluene, rt, 20 h.
ramethylsilane used as the internal standard. The specific rota-
tions were measured in a 0.5 dm tube using a JASCO DIP-4 pola-
rimeter in MeOH. Thin-layer chromatography (TLC) was per-
formed with Merck silica-gel 60Art 5554 plates, and column chro-
matography was carried out with Merck silica-gel 60 or Wakogel
C-300.
Starting Materials. H-Gly-OH, H-L-Ser-OH, and H-L-Thr-
OH were purchased from Nippon Rikagakuyakuhin Co., Ltd.
(S)-3-t-Butoxycarbonyl-2,2-dimethyloxazolidine-4-thiocar-
boxamide (7). A solution of (S)-3-t-butoxycarbonyl-2,2-dime-
thyloxazolidine-4-carboxamide4 (1.51 g, 6.19 mmol) and Lawes-
son’s reagent (1.38 g, 3.40 mmol) in DME (100 mL) was stirred at
room temperature for 18 h. The reaction mixture was concentrat-
ed in vacuo to give a residual syrup, which was purified on a sili-
ca-gel column using a mixture of hexane and EtOAc (1:1 v/v) to
give a solid material. Recrystallization from a hexane–EtOAc
gave 7 as colorless prisms. Yield 80% (1.29 g). Mp 114–115 °C.
[α]D25 +14.9° (c 1.01, MeOH). IR 3346, 3275, 3182, 3006, 2982,
1
2943, 2885, 1479, 1438 cm−1. H NMR (DMSO-d6, 80 °C) δ 1.49
(s, 9H, Boc), 1.54 and 1.74 (each s, 6H, Isop’s CH3 × 2), 3.95,
3.99 and 4.27, 4.30 (each dd, 2H, CH2, J = 3.6, 7.6, 8.9 Hz), 4.67
and 4.69 (dd, 1H, CH, J = 3.6, 7.6 Hz), 8.75 and 9.50 (each br s,
2H, NH2). Found: C, 50.86; H, 7.66; N, 10.51%. Calcd for
C11H20N2O3S: C, 50.75; H, 7.74; N, 10.76%.
Ethyl (S)-2-(3-t-Butoxycarbonyl-2,2-dimethyloxazolidin-4-
yl)thiazole-4-carboxylate (8). To a solution of 7 (533 mg, 2.05
mmol) in DME (20 mL) in the presence of KHCO3 (410 mg, 4.10
mmol) was added, with stirring, BrCH2COCOOEt (0.51 mL, 4.10

1588 Bull. Chem. Soc. Jpn., 75, No. 7 (2002)
Main Structure of Cyclothiazomycin
Scheme 4. Reagents and conditions: i) Baker’sYeast, D-Glucose, H2O, 48 h, ii) a) MsCl, Et3N, CHCl3, 0 °C, 30 min, b) NaN3, DMF,
rt, overnight, iii) a) H2, 10% Pd–C, EtOH, rt, 30 min, b) Boc2O, Et3N, CHCl3, 0 °C, 30 min, rt, 3 h, iv) a) MsCl, Et3N, 0 °C, 30
min, b) NaOAc, 15-crown-5-ether, DMF, rt, 24 h, c) K2CO3, MeOH, H2O, 0 °C, 30 min, rt, 3 h.
Scheme 5. Reagents and conditions: i) DCC, HOSu, HCl•H-Gly-OMe, CH2Cl2, 0 °C, 30 min, rt, 6 h, ii) 1 M LiOH, H2O–dioxane
(1:1 v/v), 0 °C, 30 min, rt, 1 h, iii) H-L-Thr(TBS)-OMe, DCC, HOBt, 0 °C, 30 min, rt, 6 h, iv) TBAF, THF, 0 °C, 30 min, v) a)
MsCl, Et3N, CH2Cl2, 0 °C, 30 min, b) DBU, CH2Cl2, 0 °C, 10 min, rt, 6 h, vi) H-Pro-OMe, DCC, HOBt, DMF, 0 °C, 30 min, rt, 6 h.
Scheme 6. Reagents and conditions: i) THF–CHCl3 (3:2 v/v), rt, 5 h, ii) Boc2O, Et3N, CHCl3, 0 °C, 30 min, 5 h, iii) (P)-4, BOP,
(i-Pr)2NEt, DMF, 0 °C, 30 min, rt, 4 h, iv) TFA–CHCl3 (2:3 v/v), rt, 30 min, v) (P)-6, BOP, (i-Pr)2NEt, DMF, 0 °C, 30 min, rt, 12
h.
mmol) at 0 °C. After stirring for 2 h, to the mixture were further
added, with stirring, TFAA (0.85 mL, 6.15 mmol) and pyridine
(1.07 mL, 13.33 mmol) at 0 °C. The reaction mixture was stirred
continuously for 1 h and then concentrated in vacuo to give a re-
sidual substance, which was dissolved in EtOAc (30 mL). The re-
sulting solution was washed successively with 10% citric acid (30
mL × 3), saturated NaHCO3 aqueous solution (30 mL × 3), and
brine (30 mL × 3) and then dried over anhydrous Na2SO4. Con-
centration in vacuo gave a residue, which was purified on a silica-
gel column using a mixture of hexane and EtOAc (2:1 v/v) to give

C. Shin et al.
Bull. Chem. Soc. Jpn., 75, No. 7 (2002) 1589
colorless crystals. Recrystallization from a hexane-EtOAc gave 8
as colorless prisms. Yield 89% (647 mg). Mp 131–132 °C. [α]D28
+6.2° (c 1.00, MeOH). IR 3127, 3001, 2982, 2937, 2900, 1731,
mmol) in the presence of KHCO3 (472 mg, 4.72 mmol) in DME
(30 mL) were stirred at 0 °C for 2 h. To the resulting solution was
added, with stirring, TFAA (0.98 mL, 7.08 mmol) and pyridine
(1.23 mL, 15.34 mmol) and, after stirring for 1 h, the reaction
mixture was concentrated in vacuo to give a residual substance.
The residue was dissolved in EtOAc (30 mL) and the resultant so-
lution was washed successively with 10% citric acid (30 mL × 3),
saturated NaHCO3 aqueous solution (30 mL × 3), and brine (30
mL × 3), and then dried over anhydrous Na2SO4. Concentration
in vacuo gave crude crystals, which were purified on a silica-gel
column using a mixture of hexane and EtOAc (2:1 v/v) to give 12
as colorless crystals. Yield 98% (1.03 g). Mp 134–136 °C. [α]D26
+2.4° (c 1.01, MeOH). IR 3100, 2978, 2935, 2872, 1699, 1366,
1698, 1377, 1364 cm−1 1H NMR (DMSO-d6, 80 °C) δ 1.32 (t,
.
3H, CH2CH3, J = 6.9 Hz), 1.36 (s, 9H, Boc), 1.54 and 1.67 (each
s, 6H, Isop’s CH3 × 2), 4.04–4.10 and 4.27–4.37 (each m, 4H,
CH2O, CH2CH3), 5.25 (dd, 1H, CHN, J = 2.0, 6.6 Hz), 8.38 (s,
1H, thiazole’s H). Found: C, 53.42; H, 6.31; N, 7.61%. Calcd for
C16H24N2O5S: C, 53.91; H, 6.79; N, 7.86%.
(S)-2-(3-t-Butoxycarbonyl-2,2-dimethyloxazolidin-4-yl)thia-
zole-4-carboxylic Acid (9). A solution of 8 (1.38 g, 3.87 mmol)
and 1 M LiOH (5.81 mL) in a mixture of water and dioxane (50
mL, 1:1 v/v) was stirred at 0 °C. After stirring for 30 min and at
room temperature for 3 h, the reaction mixture was washed with
diethyl ether (30 mL × 3). The aqueous layer was acidified with
citric acid hydrate to pH 4 and then extracted with EtOAc (30 mL
× 3). The combined extracts were washed with brine (30 mL ×
3) and dried over anhydrous Na2SO4. Concentration in vacuo
gave crude crystals, which were recrystallized from a hexane–
EtOAc to give 9 as colorless crystals. Yield 97% (1.26 g). Mp
230–232 °C. [α]D25 +12.0° (c 0.05, acetone). IR 3179, 3086,
1239 cm−1 1H NMR (DMSO-d6, 80 °C) δ 1.35 (t, 3H, CH2CH3, J
.
= 7.3 Hz), 1.36 (s, 9H, Boc), 1.55 and 1.71 (each s, 6H, Isop’s
CH3 × 2), 4.11 and 4.36 (each dd, 2H, CH2O, J = 1.9, 6.5, 9.2
Hz), 4.36 (q, 2H, CH2CH3, J = 7.3 Hz), 5.30 (dd, 1H, CHN, J =
1.9, 6.5 Hz), 8.26 and 8.47 (each s, 2H, thiazole’s H). Found: C,
51.44; H, 5.50; N, 9.13%. Calcd for C19H25N3O5S2: C, 51.92; H,
5.73; N, 9.56%.
(S)-2-[2-(3-t-Butoxycarbonyl-2,2-dimethyloxazolidin-4-yl)-
thiazol-4-yl]thiazole-4-carboxylic Acid (13). A solution of 12
(1.01 g, 2.30 mmol) and 1 M LiOH (3.45 mL) in a mixture of H2O
and dioxane (30 mL, 1:1 v/v) was stirred at 0 °C for 30 min and
then at room temperature for 3 h. After washing with diethyl ether
(30 mL × 3), the aqueous layer was acidified to pH 4 with citric
acid hydrate. The reaction mixture was extracted with EtOAc (30
mL × 3) and the combined extracts were washed with brine (30
mL × 3) and then dried over anhydrous Na2SO4. Concentration in
vacuo gave crude crystals, which were recrystallized from a hex-
ane–EtOAc to give 13 as colorless needles. Yield 98% (945 mg).
Mp 203–205 °C. [α]D23 +4.8° (c 1.01, MeOH). IR 3446, 3133,
2992, 2979, 1786, 1673, 1475, 1404, 1370 cm−1
.
1H NMR
(DMSO-d6, 80 °C) δ 1.37 (s, 9H, Boc), 1.54 and 1.67 (each s, 6H,
Isop’s CH3 × 2), 4.01–4.13 and 4.25–4.40 (each m, 2H, CH2O),
5.19–5.28 (m, 1H, CHN), 8.31 (s, 1H, thiazole’s H). Found: C,
51.19; H, 6.19; N, 8.21%. Calcd for C14H20N2O5S: C, 51.21; H,
6.14; N, 8.53%.
(S)-2-(3-t-Butoxycarbonyl-2,2-dimethyloxazolidin-4-yl)thia-
zole-4-carboxamide (10). A solution of 9 (1.27 g, 3.87 mmol)
and ethyl chloroformate (0.41 mL, 4.26 mmol) in THF (30 mL) in
the presence of Et3N (0.59 mL, 4.26 mmol) was strried at 0 °C for
30 min. To the resulting solution was added 28% aq NH3 (0.42
mL, 5.81 mmol) and, after stirring for 5 min, the aqueous layer
was removed. The organic layer was dried over anhydrous
Na2SO4 and concentrated in vacuo to give crude crystals. Recrys-
tallization from a hexane–EtOAc gave 10 as colorless crystals.
Yield 99% (1.26 g). Mp 157–159 °C. [α]D24 +1.8° (c 1.00,
2979, 1694, 1363 cm−1 1H NMR (DMSO-d6, 80 °C) δ 1.36 (s,
.
9H, Boc), 1.55 and 1.71 (each s, 6H, Isop’s CH3 × 2), 4.11 and
4.36 (each dd, 2H, CH2O, J = 1.7, 6.3, 9.2 Hz), 5.30 (dd, 1H,
CHN, J = 1.7, 6.3 Hz), 8.22 and 8.38 (each s, 2H, thiazole’s H ×
2). Found: C, 48.45; H, 5.09; N, 10.10%. Calcd for C17H21N3-
O5S2•0.5H2O: C, 48.56; H, 5.27; N, 9.99%.
MeOH). IR 3450, 2982, 1704, 1681, 1596 cm−1
.
1H NMR
(DMSO-d6, 80 °C) δ 1.37 (s, 9H, Boc), 1.54 and 1.67 (each s, 6H,
Isop’s CH3 × 2), 4.05–4.38 (m, 2H, CH2O), 5.15–5.27 (m, 1H,
CHN), 7.33 (br s, 2H, NH2), 8.14 (s, 1H, thiazole’s H). Found: C,
51.30; H, 6.28; N, 12.83%. Calcd for C14H21N3O4S: C, 51.36; H,
6.47; N, 12.83%.
(S,R)-2-[2-(3-t-Butoxycarbonyl-2,2-dimethyloxazolidin-4-yl)-
thiazol-4-yl]thiazole-4-carbonyl-L-Ser(TBS)-OMe (14). To a
solution of 13 (392 mg, 0.95 mmol) and H-Ser(TBS)-OMe (357
mg, 1.53 mmol) in the presence of Et3N (0.24 mL, 1.71 mmol) in
DMF (20 mL) was added, with stirring, DPPA (0.27 mL, 1.24
mmol) at 0 °C. The resulting solution was stirred for 30 min and
continuously at room temperature for 9 h and then extracted with
EtOAc (30 mL × 3). The combined extracts were washed with
10% citric acid (30 mL × 3), saturated NaHCO3 aqueous solution
(30 mL × 3), and brine (30 mL × 3) and then dried over anhy-
drous Na2SO4. Concentration in vacuo gave a residual syrup,
which was purified on a silica-gel column using a mixture of hex-
ane and EtOAc (2:1 v/v) to give 14 as a pale-yellow syrup. Yield
98% (595 mg). [α]D24 +26.0° (c 1.00, MeOH). IR 2953, 2932,
(S)-2-(3-t-Butoxycarbonyl-2,2-dimethyloxazolidin-4-yl)thia-
zole-4-thiocarboxamide (11). A solution of 10 (1.26 g, 3.85
mmol) and Lawesson’s reagent (856 mg, 2.12 mmol) in DME (30
mL) was stirred at room temperature for 10 h. The reaction mix-
ture was concentrated in vacuo to give a residual substance, which
was purified on a silica-gel column using a mixture of hexane and
EtOAc (1:1 v/v) to give yellow crystals. Recrystallization from a
hexane–EtOAc gave 11 as yellow prisms. Yield 70% (924 mg).
Mp 178–179 °C. [α]D25 −0.2° (c 1.00, MeOH). IR 3389, 3298,
1
3215, 2979, 1684, 1627 cm−1. H NMR (DMSO-d6, 80 °C) δ 1.38
2884, 2857, 1749, 1706, 1375 cm−1 1H NMR (DMSO-d6) δ 0.06
.
(s, 9H, Boc), 1.54 and 1.66 (each s, 6H, Isop’s CH3 × 2), 4.15–
4.37 (m, 2H, CH2O), 5.20–5.24 (m, 1H, CHN), 8.14 (s, 1H, thiaz-
ole’s H), 9.10 and 9.68 (each br s, NH2). Found: C, 49.28; H,
5.98; N, 12.51%. Calcd for C14H21N3O3S2: C, 48.96; H, 6.16; N,
12.23%.
Ethyl (S)-2-[2-(3-t-Butoxycarbonyl-2,2-dimethyloxazolidin-
4-yl)thiazol-4-yl]thiazole-4-carboxylate (12). A solution of 11
(810 mg, 2.36 mmol) and BrCH2COCOOEt (0.59 mL, 4.72
and 0.08 (each s, 6H, TBS’s CH3 × 2), 0.88 (s, 9H, TBS’s But),
1.36 (s, 9H, Boc), 1.56 and 1.71 (each s, 6H, Isop’s CH3 × 2),
3.72 (s, 3H, OCH3), 3.94–4.42 (m, 4H, CH2OC, Ser’s β-H), 4.65–
4.77 (m, 1H, Ser’s α-H), 5.26–5.34 (m, 1H, CHN), 8.03–8.15 (m,
1H, Ser’s NH), 8.12 and 8.32 (each s, 2H, thiazole’s H × 2).
Found: C, 51.48; H, 6.67; N, 8.80%. Calcd for C27H42N4O7S2Si:
C, 51.73; H, 6.73; N, 8.94%.
(S,R)-2-[2-(3-t-Butoxycarbonyl-2,2-dimethyloxazolidin-4-yl)-

1590 Bull. Chem. Soc. Jpn., 75, No. 7 (2002)
Main Structure of Cyclothiazomycin
thiazol-4-yl]thiazole-4-thiocarbonyl-L-Ser(TBS)-OMe (15).
Similarly to the case of 11, a solution of 14 (592 mg, 0.94 mmol)
and Lawesson’s reagent (209 mg, 0.52 mmol) in DME (10 mL)
was woked up at 50 °C for 16 h. The reaction mixture was con-
centrated in vacuo to give a residual syrup, which was purified on
a silica-gel column using a mixture of hexane and EtOAc (3:1 v/v)
to give 15 as a yellow syrup. Yield 82% (495 mg). [α]D24 +60.2°
(c 1.00, MeOH). IR 2952, 2931, 1778, 1706, 1521 cm−l. 1H
NMR (DMSO-d6) δ 0.07 and 0.08 (each s, 6H, TBS’s CH3 × 2),
0.88 (s, 9H, TBS’s But), 1.37 (s, 9H, Boc), 1.56 and 1.72 (each s,
6H, Isop’s CH3 × 2), 3.75 (s, 3H, OCH3), 4.05–4.42 (m, 4H,
CH2OC, Ser’s β-H), 5.23–5.38 (m, 2H, CHN, Ser’s α-H), 8.11 and
8.51 (each s, 2H, thiazole’s H × 2), 9.90 (br d, 1H, Ser’s NH, J =
6.6 Hz). Found: C, 50.69; H, 6.37; N, 8.62%. Calcd for C27H42-
N4O7S2Si: C, 50.44; H, 6.58; N, 8.71%.
11.91%.
Methyl (S,R)-2-{2-[2-(1-t-Butoxycarbonylamino-2-t-butyl-
diphenylsiloxyethyl)thiazol-4-yl]thiazol-4-yl}-4,5-dihydrothia-
zole-4-carboxylate (19). To a solution of 18 (100 mg, 0.21
mmol) in CHCl3 (5 mL) were added, with stirring, TPS-Cl (6 µL,
0.25 mmol) and imidazole (29 mg, 0.42 mmol) at 0 °C. After stir-
ring for 12 h, the reaction mixture was washed with brine (5 mL ×
3) and dried over anhydrous Na2SO4. Concentration in vacuo
gave a residual syrup, which was purified on a silica-gel column
using a mixture of hexane and EtOAc (3:1 v/v) to give 19 as a col-
orless syrup. Yield 97% (145 mg). [α]D23 +10.0° (c 0.06, MeOH).
IR 2926, 2855, 1717, 1489 cm−1 1H NMR δ 0.97 (s, 9H, TPS’s
.
But), 1.49 (s, 9H, Boc), 3.69 (dd, 2H, thiazoline’s CH2, J = 5.8,
9.2 Hz), 3.86 (s, 3H, OCH3), 3.97–4.18 (m, 2H, CH2O), 5.10–5.20
(m, 1H, CHN), 5.33 (t, 1H, thiazoline’s CH, J = 9.2 Hz), 6.58–
6.68 (m, 1H, NH), 7.27–7.62 (m, 10H, TPS’s Ph × 2), 8.04 and
8.05 (each s, 2H, thiazole’s H × 2). Found: C, 57.81; H, 5.39: N,
8.01%. Calcd for C34H40N4O5S3Si: C, 57.60; H, 5.67; N, 7.90%.
Methyl 6-Dimethoxymethyl-2-oxo-1,2-dihydropyridine-3-
carboxylate (22). A solution of 20 (10.0 g, 51.5 mmol) and 6 M
KOH (100 mL) in EtOH (100 mL) was refluxed for 8 h. Evapora-
tion of EtOH gave an aqueous reaction mixture, which was
washed with diethyl ether (30 mL × 3). The aqueous layer was
acidified to pH 4 with citric acid hydrate and the resulting solution
was extracted with EtOAc (100 mL × 5). The combined extracts
were washed with brine (50 mL) and dried over anhydrous
Na2SO4. Concentration in vacuo gave a residual substance 21,
which was dissolved in MeOH (200 mL). To the resulting solu-
tion was added p-toluenesulfonic acid hydrate (4.43 g) and, after
refluxing overnight, the resultant solution was neutralized with
Et3N at room temperature. Concentration in vacuo gave crude
crystals, which were purified on a silica gel column using a mix-
ture of CHCl3 and acetone (7:1 v/v) to give colorless crystals. Re-
crystallization from a hexane-EtOAc gave 22 as colorless needles.
Yield 63% (7.73 g) from 20 in two steps. Mp 94–95 °C. IR 3046,
(S,R)-2-[2-(3-t-Butoxycarbonyl-2,2-dimethyloxazolidin-4-yl)-
thiazol-4-yl]thiazole-4-thiocarbonyl-L-Ser-OMe (16).
A so-
lution of 15 (486 mg, 0.76 mmol) and TBAF (1.13 mL, 1 M in
THF) in THF (10 mL) was stirred at 0 °C for 1 h. Evaporation of
THF gave a residual substance, which was purified on a silica-gel
column using a mixture of hexane and EtOAc (1:1 v/v) to give 16
as a yellow amorphous material. Yield 66% (264 mg). [α]D24
+31.2° (c 1.00, MeOH). IR 3335, 2979, 1744, 1704, 1523, 1366
cm−1 1H NMR (DMSO-d6, 80 °C) δ 1.14–1.47 (m, 10H, Boc,
.
OH), 1.56 and 1.72 (each s, 6H, Isop’s CH3 × 2), 3.73 (s, 3H,
OCH3), 3.90–4.42 (m, 4H, CH2OC, Ser’s β-H), 5.17–5.38 (m, 2H,
CHN, Ser’s α-H), 8.28 and 8.50 (each s, 2H, thiazole’s H × 2),
9.90–10.01 (m, 1H, Ser’s NH). Found: C, 47.96; H, 5.39; N,
10.43%. Calcd for C21H28N4O6S3: C, 47.71; H, 5.34; N, 10.60%.
Methyl (S,R)-2-{2-[2-(3-t-Butoxycarbonyl-2,2-dimethylox-
azolidin-4-yl)thiazol-4-yl]thiazol-4-yl}-4,5-dihydrothiazole-4-
carboxylate (17). To a solution of 16 (249 mg, 0.47 mmol) in
THF (10 mL) were added, with stirring, Ph3P (185 mg, 0.71
mmol) and DEAD (40% in toluene; 0.28 mL, 0.71 mmol) at 0 °C.
After stirring for 1 h, evaporation of THF gave a residual sub-
stance, which was purified on a silica-gel column using a mixture
of hexane and EtOAc (1:1 v/v) to give 17 as a colorless amor-
phous material. Yield 72% (173 mg). [α]D24 +3.7° (c 1.02,
2944, 2830, 1740, 1641, 1599, 1566 cm−1 1H NMR δ 3.42 (s,
.
6H, CH(OCH3)2), 3.92 (s, 3H, OCH3), 5.31 (s, 1H, CH(OCH3)2),
6.60 (d, 1H, pyridone’s H, J = 7.6 Hz), 8.25 (d, 1H, pyridone’s H,
J = 7.6 Hz), 10.69–10.92 (br s, 1H, NH). Found: C, 53.06; H,
5.75; N, 6.47%. Calcd for C10H13NO5: C, 52.86; H, 5.77; N,
6.16%.
MeOH). IR 2980, 1743, 1704 cm−1 1H NMR (DMSO-d6, 80 °C)
.
δ 1.36 (s, 9H, Boc), 1.55 and 1.71 (each s, 6H, Isop’s CH3 × 2),
3.76 (s, 3H, OCH3), 3.60–4.40 (m, 4H, thiazoline’s CH2, CH2O),
5.27–5.42 (m, 2H, CHN, thiazoline’s CH), 8.20 and 8.29 (each s,
2H, thiazole’s H). Found: C, 49.37; H, 5.51; N, 10.92%. Calcd
for C21H26N4O5S3: C, 49.39; H, 5.13; N, 10.97%.
Methyl 6-Dimethoxymethyl-2-trifluoromethylsulfonyloxy-
pyridine-3-carboxylate (23). To a solution of 22 (2.0 g, 8.80
mmol) in pyridine (50 mL) were added, with stirring, DMAP
(1.51 g, 12.32 mmol) and Tf2O (1.59 g, 9.68 mmol) at 0 °C. After
stirring for 30 min, the reaction mixture was concentrated in vacuo
to give a residual substance, which was dissolved in EtOAc (70
mL). The resulting solution was washed with a saturated NaHCO3
aqueous solution (10 mL × 3), and brine (10 mL × 3) and then
dried over anhydrous Na2SO4. Concentration in vacuo gave a syr-
up, which was purified on a silica-gel column using a mixture of
hexane and EtOAc (1:1 v/v) to give 23 as a colorless syrup. Yield
Methyl (S,R)-2-{2-[2-(1-t-Butoxycarbonylamino-2-hydroxy-
ethyl)thiazol-4-yl]thiazol-4-yl}-4,5-dihydrothiazole-4-carboxy-
late (18). A solution of 17 (173 mg, 0.34 mmol) in a mixture of
TFA and CHCl3 (10 mL, 4:96 v/v) was stirred at room tempera-
ture for 2 h. The reaction mixture was neutralized with saturated
NaHCO3 aqueous solution and the organic layer was washed with
brine (10 mL × 3) and dried over anhydrous Na2SO4. Concentra-
tion in vacuo gave a residual substance, which was purified on a
silica-gel column using a mixture of hexane and EtOAc (1:1 v/v)
to give 18 as colorless crystals. Yield 70% (112 mg). Mp 207–
209 °C. [α]D23 +1.3° (c 0.31, MeOH). IR 3439, 3336, 1732, 1700,
81% (2.56 g). IR 3478, 2932, 2836, 2248, 1725, 1608, 1557 cm−1
.
1H NMR δ 3.44 (s, 6H, CH(OCH3)2), 4.00 (s, 3H, OMe), 5.29 (s,
1H, CH(OCH3)2), 7.75 (d, 1H, pyridine’s H, J = 7.8 Hz), 8.50 (d,
1H, pyridine’s H, J = 7.8 Hz). Found: C, 36.65; H, 3.39; N,
3.84%. Calcd for C11H12NO7SF3: C, 36.77; H, 3.37; N, 3.90%.
Methyl 6-Dimethoxymethyl-2-(1-ethoxyethenyl)pyridine-3-
carboxylate (24). To a solution of 23 (2.64 g, 7.35 mmol) in tol-
uene (50 mL) were added Pd(OAc)2 (0.25 g, 1.11 mmol), dppp
(0.45 g, 1.09 mmol), ethyl vinyl ether (8.49 mL, 88.30 mmol) and
1586, 1524 cm−1 1H NMR δ 1.48 (s, 9H, Boc), 178–2.04 (m, 1H,
.
OH), 3.68 (dd, 2H, thiazoline’s CH2, J = 5.2, 9.4 Hz), 3.84 (s, 3H,
OCH3), 3.93–4.18 (m, 2H, CH2O), 5.02–5.15 (m, 1H, CHN), 5.32
(t, 1H, thiazoline’s CH, J = 9.4 Hz), 6.70–6.80 (m, 1H, NH), 8.03
and 8.04 (each s, 2H, thiazole’s H × 2). Found: C, 45.59; H, 4.41;
N, 11.96%. Calcd for C18H22N4O5S3: C, 45.94; H, 4.71; N,

C. Shin et al.
Bull. Chem. Soc. Jpn., 75, No. 7 (2002) 1591
Et3N (3.08 mL, 22.10 mmol) at room temperature. The resulting
suspension was refluxed for 6 h and then concentrated in vacuo to
give a residual substance, which was dissolved in CHCl3 (70 mL).
The obtained solution was washed with brine (30 mL × 2) and
dried over anhydrous Na2SO4. Concentration in vacuo gave a re-
sidual syrup, which was purified on a silica-gel column using a
mixture of hexane and EtOAc (1:1 v/v) to give 24 as a colorless
syrup. Without purification, the compound 24 was used to the
next reaction.
mL, 1.29 mmol) and Ms-Cl (0.10 mL, 1.23 mmol) at 0 °C. After
stirring for 10 min, the reaction mixture was mixed with diethyl
ether (60 mL) and the resulting solution was washed with brine
(30 mL), and then dried over anhydrous Na2SO4. Concentration
in vacuo gave a residual substance, which was purified on a silica-
gel column using a mixture of hexane and EtOAc (3:1 v/v) to give
a colorless syrup. The obtained syrup was again dissolved in
DMF (40 mL) and the resulting solution was stirred with NaN3
(0.31 g, 4.71 mmol) at room temperature for 30 min. The reaction
mixture was extracted with EtOAc (30 mL × 3) and the combined
extracts were washed with brine (30 mL) and then dried over an-
hydrous Na2SO4. Concentration in vacuo gave a residual syrup,
which was purified on a silica-gel column using a mixture of hex-
ane and EtOAc (5:1 v/v) to give 28 as a colorless syrup. Yield
92% (0.42 g). IR 3304, 2902, 2074, 1902, 1821, 1737, 1587 cm−l.
1H NMR δ 1.08 (s, 9H, TPS’s But), 1.58 (d, 3H, CH3, J = 6.6 Hz),
3.42 and 3.47 (each s, 6H, CH(OCH3)2), 4.54 (d, 1H, CHN3, J =
6.8 Hz), 4.77 (ABq, 2H, CH2, J = 13.2 Hz), 5.34 (s, 1H,
CH(OCH3)2), 7.34–7.46 and 7.62–7.69 (each m, 10H, TPS’s Ph ×
2), 7.54 (d, 1H, pyridine’s H, J = 8.1 Hz), 7.77 (d, 1H, pyridine’s
H, J = 8.1 Hz). Found: C, 65.68; H, 6.91; N, 11.60%. Calcd for
C27H34N4O3Si: C, 66.04; H, 6.98; N, 11.42%.
Methyl
2-Acetyl-6-dimethoxymethylpyridine-3-carboxy-
late (25). To a solution of 24 (1.43 g, 5.08 mmol) in THF (5 mL)
was added, with stirring, 70% AcOH (50 mL) at room tempera-
ture. After stirring overnight, the reaction mixture was concentrat-
ed in vacuo to give a residual syrup, which was purified on a sili-
ca-gel column using a mixture of hexane and EtOAc (1:1 v/v) to
give 25 as a pale-yellow syrup. Yield 91% (1.28 g). IR 2926,
2838, 2620, 1704, 1584 cm−1 1H NMR δ 2.69 (s, 3H, CH3), 3.43
.
(s, 6H, CH(OCH3)2), 3.91 (s, 3H, OCH3), 5.37 (s, 1H, CH-
(OCH3)2), 7.73 (d, 1H, pyridine’s H, J = 8.1 Hz), 8.04 (d, 1H, py-
ridone’s H, J = 8.1 Hz). Found: C, 56.56; H, 6.08; N, 5.31%.
Calcd for C12H15NO5: C, 56.91; H, 5.97; N, 5.53%.
(RS)-2-(1-Hydroxyethyl)-3-hydroxymethyl-6-dimethoxyme-
thylpyridine (26). To a solution of 25 (2.58 g, 10.20 mmol) in
EtOH (50 mL) were added, with stirring, CaCl2 (6.80 g, 61.27
mmol) and NaBH4 (2.32 g, 61.33 mmol) at 0 °C. After stirring for
30 min and for 3 h at room temperature, a saturated NH4Cl aque-
ous solution (50 mL) was added to the reaction mixture. Evapora-
tion in vacuo gave a residual aqueous layer. The layer was extract-
ed with EtOAc (50 mL × 5) and the combined extracts were dried
over anhydrous Na2SO4. Concentration in vacuo gave a syrup,
which was purified on a silica-gel column using EtOAc to give 26
as a colorless syrup. Yield 94% (2.17 g). IR 3384, 2935, 1579
(RS)-2-(1-t-Butoxycarbonylaminoethyl)-3-t-butyldiphenyl-
siloxymethyl-6-dimethoxymethylpyridine (30). A suspension
of 28 (1.0 g, 2.03 mmol) and 10% Pd–C (0.10 g) in EtOH (50 mL)
was stirred under H2 gas stream for 30 min at room temperature.
After the Pd–C was filtered off, the filtrate was concentrated in
vacuo and the residual substance 29, which was in situ dissolved
in CHCl3 (50 mL). To the resulting solution were added, with stir-
ring, Et3N (0.28 mL, 2.03 mmol) and Boc2O (0.53 g, 2.40 mmol)
at 0 °C. After stirring for 30 min and at room temperature for 4 h,
the reaction mixture was mixed with diethyl ether (70 mL), and
then washed with 10% citric acid (30 mL × 2), saturated NaHCO3
aqueous solution (30 mL × 2) and brine (30 mL × 2), and finally
dried over anhydrous Na2SO4. Concentration in vacuo gave a re-
sidual syrup, which was purified on a silica-gel column using a
mixture of hexane and EtOAc (1:1 v/v) to give 30 as a colorless
syrup. Yield 98% (1.14 g) from 28 in two steps. IR 3418, 2914,
cm−1 1H NMR δ 1.41 (d, 3H, CH3, J = 6.4 Hz), 3.38 and 3.40
.
(each s, 6H, CH(OCH3)2), 3.43–3.46 (m, 1H, OH), 4.68 (s, 2H,
CH2), 4.81-5.00 (m, 2H, CHOH, OH), 5.34 (s, 1H, CH(OCH3)2),
7.46 (d, 1H, pyridine’s H, J = 7.8 Hz), 7.81 (d, 1H, pyridine’s H, J
= 7.8 Hz). Found: C, 57.94; H, 7.98; N, 6.24%. Calcd for
C11H17NO4: C, 58.14; H, 7.54; N, 6.16%.
(RS)-3-t-Butyldiphenylsiloxymethyl-6-dimethoxymethyl-2-
(1-hydroxyethyl)pyridine (27). To a solution of 26 (0.31 g,
1.36 mmol) in CH2Cl2 (30 mL) were added, with stirring, Et3N
(0.23 mL, 1.64 mmol), DMAP (0.02 g, 0.16 mmol), and TPS-Cl
(0.36 mL, 1.55 mmol) at 0 °C for 30 min. After stirring at room
temperature for 2 h, diethyl ether (40 mL) was added to the reac-
tion mixture. The resulting solution was washed successively
with 10% citric acid (30 mL × 3), a saturated NaHCO3 aqueous
solution (30 mL × 3), and brine (30 mL × 3) and then dried over
anhydrous Na2SO4. Concentration in vacuo gave a residual syrup,
which was purified on a silica-gel column using a mixture of hex-
ane and EtOAc (1:1 v/v) to give 27 as a colorless syrup. Yield
86% (0.54 g). IR 3448, 2854, 2230, 1959, 1893, 1821, 1728, 1584
1707, 1575 cm−1 1H NMR δ 1.09 (s, 9H, TPS’s But), 1.26 (d, 3H,
.
CH3, J = 6.6 Hz), 1.41 (s, 9H, Boc), 3.40 (s, 6H, CH(OCH3)2),
4.72–4.93 (m, 3H, CHNH and CH2), 5.36 (s, 1H, CH(CH3)2), 6.05
(br d, 1H, NH, J = 7.3 Hz), 7.33–7.47 and 7.63–7.69 (each m,
11H, TPS’s Ph × 2 and pyridine’s H), 7.85 (d, 1H, pyridine’s H, J
= 8.1 Hz). Found: C, 67.64; H, 8.05; N, 4.55%. Calcd for
C32H44N2O5Si: C, 68.05; H, 7.85; N, 4.96%.
Methyl (RS)-2-[2-(1-t-Butoxycarbonylaminoethyl)-3-(t-bu-
tyldiphenylsiloxymethyl)pyridin-6-yl]thiazole-4-carboxylate
(32). After a solution of 30 (3.0 g, 5.31 mmol) and 2 M HCl (40
mL) in THF (40 mL) was stirred at room temperature overnight,
the reaction mixture was neutralized with saturated NaHCO3
aqueous solution. After evaporating THF, the residue was extract-
ed with EtOAc (50 mL × 3). The combined extracts were washed
with saturated NaHCO3 aqueous solution (50 mL × 3) and brine
(50 mL × 2), and then dried over anhydrous Na2SO4. Concentra-
tion in vacuo gave a residual substance 30, which was dissolved in
toluene (80 mL). The resultant solution was stirred with H-L-Cys-
OMe•HCl (1.82 g, 10.62 mmol) in the presence of Et3N (1.48 mL,
10.62 mmol) at 0 °C for 10 h. Concentration in vacuo gave a re-
sidual substance, which was dissolved again in EtOAc (100 mL)
and then washed with 10% citric acid (40 mL × 3), a saturated
NaHCO3 aqueous solution (40 mL × 3), brine (40 mL × 3) and
cm−1 1H NMR δ 1.09 (s, 9H, TPS’s But), 1.27 (d, 3H, CH3, J =
.
6.1 Hz), 1.84 (s, 1H, OH), 3.40 and 3.43 (each s, 6H, CH-
(OCH3)2), 4.69–4.83 (m, 3H, CHOH, CH2), 5.36 (s, 1H, CH-
(OCH3)2), 7.34–7.45 and 7.64–7.70 (each m, 10H, TPS’s Ph × 2),
7.50 (d, 1H, pyridine’s H, J = 8.1 Hz), 7.91 (d, 1H, pyridine’s H, J
= 8.1 Hz). Found: C, 69.35; H, 7.77; N, 3.18%. Calcd for
C27H35NO4Si: C, 69.64; H, 7.58; N, 3.18%.
(RS)-2-(1-Azidoethyl)-3-t-butyldiphenylsiloxymethyl-6-di-
methoxymethylpyridine (28). To a solution of 27 (0.44 g, 0.94
mmol) in CH2Cl2 (40 mL) were added, with stirring, Et3N (0.18

1592 Bull. Chem. Soc. Jpn., 75, No. 7 (2002)
Main Structure of Cyclothiazomycin
then dried over anhydrous Na2SO4. After concentrating in vacuo,
the obtained residue was dissolved in toluene (80 mL); to the re-
sulting solution was added MnO2 (9.23 g, 106.2 mmol), and the
mixture was stirred at room temperature overnight. After removal
of MnO2, the reaction mixture was concentrated in vacuo to give a
viscous syrup, which was purified on a silica-gel column using a
mixture of hexane and EtOAc (3:1 v/v) to give 32 as a colorless
amorphous material. Yield 57% (1.91 g). IR 3439, 2931, 1731,
ridine’s H, J = 8.2 Hz), 8.40 (s, 1H, thiazole’s H). Found: C,
60.27; H, 5.41; N, 8.58%. Calcd for C25H27N3O6S: C, 60.35; H,
5.47; N, 8.45%.
Phenacyl (RS)-2-(1H-2-t-Butoxycarbonyl-1-oxo-2,3-dihy-
dropyrrolo[3,4-b]pyridin-5-yl)thiazole-4-carboxylate
(36).
To a solution of 35 (1.07 g, 2.15 mmol) in acetone (75 mL) was
added 2.67 M Jones reagent (1.21 mL, 3.23 mmol) at 0 °C. After
stirring for 40 min, the reaction mixture was mixed with i-PrOH
(40 mL) and the precipitated Cr salt was filtered off. The filtrate
was made to pH 9 with a saturated NaHCO3 aqueous solution.
Evaporation of acetone gave a residual solution, which was ex-
tracted with EtOAc (40 mL × 3); the combined extracts were
washed with brine (30 mL × 3) and then dried over anhydrous
Na2SO4. Concentration in vacuo gave residual crystals, which
were purified on a silica-gel column using a mixture of hexane and
EtOAc (1:2 v/v) to give crude crystals. Recrystallization from a
hexane–EtOAc gave 36 as a colorless amorphous material. Yield
1587 cm−1 1H NMR δ 1.10 (s, 9H, TPS’s But), 1.34 (d, 3H, CH3,
.
J = 6.6 Hz), 1.42 (s, 9H, Boc), 3.99 (s, 3H, OMe), 4.76–4.95 (m,
3H, CHNH, CH2), 5.75 (br d, 1H, NH, J = 8.3 Hz), 7.33–7.45 and
7.64–7.69 (each m, 10H, TPS’s Ph × 2), 7.86 (br d, 1H, pyridine’s
H, J = 8.6 Hz), 8.18 (d, 1H, pyridine’s H, J = 7.8 Hz), 8.26 (s,
1H, thiazole’s H). Found: C, 64.52; H, 6.86; N, 6.29%. Calcd for
C34H41N3O5SSi: C, 64.63; H, 6.54; N, 6.65%.
(RS)-2-[2-(1-t-Butoxycarbonylaminoethyl)-3-(t-butyldiphen-
ylsiloxymethyl)pyridin-6-yl]thiazole-4-carboxylic Acid (33).
To a solution of 32 (6.20 g, 9.81 mmol) in H2O–dioxane (60 mL,
1:1 v/v) was added, with stirring, 1 M LiOH (11.77 mL, 11.77
mmol) at 0 °C. After stirring for 10 min and for 5 h at room tem-
perature, the resultant solution was acidified with citric acid hy-
drate to pH 4. The reaction mixture was extracted with EtOAc (50
mL × 3) and the combined extracts were washed with brine (30
mL × 2), and then dried over anhydrous Na2SO4. Concentration
in vacuo gave a colorless syrup 33, which was intact used the next
reaction.
83% (0.88 g). IR 3749, 3417, 2931, 2360, 1738, 1596 cm−1 1H
.
NMR δ 1.63 (s, 9H, Boc), 1.77 (d, 3H, CH3, J = 6.6 Hz), 5.14 (q,
1H, CHN, J = 6.6 Hz), 5.67 (s, 2H, CH2), 7.50–7.68 and 7.97–
8.00 (each m, 5H, Pac’s Ph), 8.27 (d, 1H, pyridine’s H, J = 7.9
Hz), 8.48 (d, 1H, pyridine’s H, J = 7.9 Hz), 8.50 (s, 1H, thiazole’s
H). Found: C, 61.17; H, 4.52; N, 8.38%. Calcd for C25H23N3O6S:
C, 60.84; H, 4.70; N, 8.51%.
(RS)-2-(1H-2-t-Butoxycarbonyl-1-oxo-2,3-dihydropyrrolo-
[3,4-b]pyridin-5-yl)thiazole-4-carbonyl-L-Ser(TBS)-OBut (38).
A solution of 36 (0.52 g, 1.05 mmol) and K2CO3 (0.44 g, 3.15
mmol) in water–THF (40 mL, 1:2 v/v) was stirred at 0 °C for 30
min and then at room temperature for 8 h. Evaporation of THF
gave an aqueous solution, which was acidified to pH 4 with citric
acid hydrate. The reaction mixture was extracted with EtOAc (20
mL × 2) and the combined extracts were washed with brine (10
mL × 2) and then dried over anhydrous Na2SO4. Concentration in
vacuo gave a free acid 37 as a residual substance, which was in
situ dissolved in DMF (30 mL). To the resulting solution were
added, with stirring, H-L-Ser(TBS)-OBut (0.32 g, 1.16 mmol),
Et3N (0.23 mL, 1.68 mmol), and DPPA (0.30 mL, 1.37 mmol) at 0
°C. After stirring for 30 min and at room temperature overnight,
water (30 mL) was added to the reaction mixture, and the resulting
solution was extracted with EtOAc (20 mL × 3). The combined
extracts were washed with 10% citric acid (20 mL × 2), saturated
NaHCO3 aqueous solution (20 mL × 2), and brine (20 mL × 2)
and then dried over anhydrous Na2SO4. Concentration in vacuo
gave a residue, which was purified on a silica-gel column using a
mixture of CHCl3 and acetone (1:1 v/v) to give 38 as a colorless
amorphous material. Yield 70% (0.47 g). IR 3418, 2932, 2857,
Phenacyl (RS)-2-[2-(1-t-Butoxycarbonylaminoethyl)-3-(t-
butyldiphenylsiloxymethyl)pyridin-6-yl]thiazole-4-carboxy-
late (34). To a solution of 33 (2.36 g, 3.82 mmol) in DMF (50
mL) were added, with stirring, Et3N (0.80 mL, 5.73 mmol) and
Pac-Br (1.14 g, 5.37 mmol) at 0 °C. After stirring for 30 min and
at room temeperature for 6 h, the reaction mixture was added to
water (50 mL). The resulting solution was extracted with EtOAc
(30 mL × 3) and the combined extracts were dried over anhy-
drous Na2SO4. Concentration in vacuo gave a residual syrup,
which was purified on a silica-gel column using a mixture of hex-
ane and EtOAc (1:1 v/v) to give 34 as a colorless amorphous ma-
terial. Yield 83% (2.45 g). IR 3435, 3070, 2960, 2930, 2891,
2857, 2359, 1704, 1586 cm−1 1H NMR δ 1.10 (s, 9H, TPS’s But),
.
1.34 (d, 3H, CH3, J = 6.6 Hz), 1.43 (s, 9H, Boc), 4.87 (s, 2H,
CH2), 4.75–4.97 (m, 1H, CHN), 5.66 (s, 2H, Pac’s CH2), 5.76 (br
d, 1H, NH, J = 7.9 Hz), 7.35–7.72 (each m, 15H, TPS’s and Pac’s
Ph × 3), 7.87 (d, 1H, pyridine’s H, J = 7.9 Hz), 8.20 (d, 1H, pyri-
dine’s H, J = 7.9 Hz), 8.40 (s, 1H, thiazole’s H). Found: C, 66.48;
H, 6.01; N, 5.77%. Calcd for C41H45N3O6SSi: C, 66.91; H, 6.16;
N, 5.71%.
Phenacyl (RS)-2-[2-(1-t-Butoxycarbonylaminoethyl)-3-(hy-
1783, 1748, 1682, 1594, 1537, 1506 cm−1 1H NMR δ each 0.05
.
droxymethyl)pyridin-6-yl]thiazole-4-carboxylate (35). To
a
(each s, 6H, TBS’s CH3 × 2), 0.91 (s, 9H, TBS’s But), 1.50 (s, 9H,
Boc), 1.62 (s, 9H, OBut), diastereomer 1.74 and 1.75 (each d, 3H,
CH3, J = each 6.6 Hz), 3.94 and 4.17 (dABq, 2H, Ser’s β-H, J =
2.3, 10.1 Hz), 4.68–4.78 (m, 1H, Ser’s α-H), diastereomer each
5.12 (each q, 1H, CHCH3, J = 6.6 Hz), 8.16 (br d, 1H, NH, J =
8.6 Hz), 8.25 (d, 1H, pyridine’s H, J = 8.3 Hz), 8.29 (s, 1H, thiaz-
ole’s H), 8.33 (d, 1H, pyridine’s H, J = 8.3 Hz). Found: C, 56.75;
H, 7.15; N, 8.45%. Calcd for C30H44N4O7SSi: C, 56.94; H, 7.01;
N, 8.85%.
solution of 34 (1.0 g, 1.36 mmol) in THF (30 mL) was added, with
stirring, TBAF (2.04 mL of 1 M THF, 2.04 mmol) at 0 °C. After
stirring for 30 min, the reaction mixture was concentrated in vacuo
to give a residual substance. The residue was purified on a silica-
gel column using a mixture of hexane and EtOAc (1:1 v/v) to give
colorless crystals, which were recrystallized from a hexane–
EtOAc to give 35 as colorless crystals. Yield 77% (0.52 g). Mp
173–174 °C. IR 3450, 3377, 3133, 2974, 2930, 2888, 1734, 1699,
1663, 1599, 1583 ,1518 cm−1
.
1H NMR δ 1.41 (s, 9H, Boc), 1.51
2-{3-Benzyloxycarbonyl-2-[(1SR)-1-t-butoxycarbonylamino-
ethyl]pyridin-6-yl}thiazole-4-carbonyl-L-Ser(TBS)-OBut (40).
A solution of 38 (2.59 g, 4.09 mmol) and 1 M LiOH (12.27 mL,
12.27 mmol) in THF–water (100 mL, 2:1 v/v) was stirred at 0 °C
for 30 min and at room temperature for 1 h. Evaporation of THF
(d, 3H, CH3, J = 6.6 Hz), 3.95–4.80 (m, 1H, OH), 4.54–4.68 and
4.90–5.10 (each m, 2H, CH2), 5.57 (br d, 1H, NH, J = 8.9 Hz),
5.65 (s, 2H, Pac’s CH2), 7.48–7.68 and 7.92–8.01 (each m, 5H,
Pac’s Ph), 7.84 (d, 1H, pyridine’s H, J = 8.2 Hz), 8.19 (d, 1H, py-

C. Shin et al.
Bull. Chem. Soc. Jpn., 75, No. 7 (2002) 1593
gave a residual aqueous solution, which was extracted with EtOAc
(50 mL × 3). The combined extracts were dried over anhydrous
Na2SO4 and concentrated in vacuo to give a residue 39, which was
in situ dissolved in DMF (50 mL). To the resulting solution were
added, with stirring, Et3N (1.31 mL, 9.41 mmol) and Bn-Br (0.97
mL, 8.18 mmol) at 0 °C. After stirring for 30 min and at room
temperature for 12 h, water (50 mL) was added to the reaction
mixture and the resulting solution was extracted with EtOAc (30
mL × 3). The combined extracts were washed with 10% citric
acid (30 mL × 3), saturated NaHCO3 aqueous solution (30 mL ×
3), and brine (30 mL × 3), and then dried over anhydrous Na2SO4.
Concentration in vacuo gave a residue, which was purified on a
silica-gel column using a mixture of hexane and EtOAc (2:1 v/v)
to give 40 as a colorless amorphous material. Yield 67% (2.03 g)
in two steps from 38. IR 3419, 2977, 2931, 2885, 2857, 1720,
Hz), 4.12–4.20 and 4.28–4.46 (each m, 2H, Ser’s β-H), 5.29–5.34
(m, 1H, Ser’s α-H), 5.40 (s, 2H, Bn’s CH2), 5.63–5.91 (m, 2H,
BocNH, CH3CH), 7.34–7.49 (m, 5H, Bn’s Ph), 8.14 (d, 1H, pyri-
dine’s H, J = 8.3 Hz), 8.34 (d, 1H, pyridine’s H, J = 8.3 Hz), 8.55
(s, 1H, thiazole’s H), 9.98 (br d, 1H, NH, J = 7.3 Hz). 43: Yield
41% (76 mg). Mp 141–145 °C. [α]D24 +95.7° (c 0.92, CHCl3). IR
3551, 3428, 3331, 2978, 2932, 1710, 1581, 1509 cm−1 1H NMR
.
δ 1.43 (s, 9H, Boc), 1.45 (d, 3H, CH3, J = 6.6 Hz), 1.55 (s, 9H,
OBut), 2.15–2.17 (m, 1H, OH), 4.12–4.20 and 4.28–4.36 (each m,
2H, Ser’s β-H), 5.28–5.33 (m, 1H, Ser’s α-H), 5.40 (s, 2H, Bn’s
CH2), 5.63–5.91 (m, 2H, BocNH, CH3CH), 7.36–7.49 (m, 5H,
Bn’s Ph), 8.14 (d, 1H, pyridine’s H, J = 8.3 Hz), 8.30 (d, 1H, pyri-
dine’s H, J = 8.3 Hz), 8.55 (s, 1H, thiazole’s H), 9.98 (br d, 1H,
NH, J = 7.3 Hz). Found: C,57.92; H, 6.01; N, 8.63%. Calcd for
C31H38N4O7S2: C, 57.93; H, 5.96; N, 8.72%.
1677, 1584, 1536 cm−1
.
1H NMR δ 0.04 and 0.05 (each s, 6H,
t-Butyl (4S)-2-(2-{3-Benzyloxycarbonyl-2-[(1R)-t-butoxy-
carbonylaminoethyl]pyridin-6-yl}thiazol-4-yl)-4,5-dihydrothi-
azole-4-carboxylate (44). To a solution of 42 (460 mg, 0.72
mmol) in THF (10 mL) were added, with stirring, Ph3P (0.28 g,
1.08 mmol) and DEAD (0.28 mL, 1.08 mmol) (40% in toluene) at
0 °C. After stirring for 30 min, THF in the reaction mixture was
evaporated and the residual substance was purified on a silica-gel
column using a mixture of hexane and EtOAc (2:1 v/v) to give 44
as a colorless syrup. 44: Yield 69% (340 mg). [α]D26 −50.9° (c
0.70, CHCl3). IR 3435, 3113, 2977, 2931, 2360, 1719, 1606,
TBS’s CH3 × 2), 0.90 (s, 9H, TBS’s But), 1.37–1.50 (m, 12H,
CH3, Boc), 1.50 (s, 9H, O-t-Bu), 4.33 and 4.56 (dABq, 2H, Ser’s
β-H, J = 2.3, 10.1 Hz), 4.70–4.79 (m, 1H, Ser’s α-H), 5.40 (s, 2H,
Bn’s CH2), 5.68–5.88 (m, 2H, NHBoc, CH3CH), 7.35–7.52 (m,
5H, Bn’s Ph), diastereomer 8.08 and 8.09 (each d, 1H, pyridine’s
H, J = each 8.3 Hz), 8.14 (d, 1H, NH, J = 8.9 Hz), 8.26 (s, 1H,
thiazole’s H), 8.33 (d, 1H, pyridine’s H, J = 8.3 Hz). Found: C,
59.88; H, 7.13; N, 7.17%. Calcd for C37H52N4O8SSi: C, 59.97; H,
7.07; N, 7.56%.
2-{3-Benzyloxycarbonyl-2-[(1RS)-1-t-butoxycarbonylamino-
ethyl]pyridin-6-yl}thiazole-4-thiocarbonyl-L-Ser(TBS)-OBut
(41). A solution of 40 (1.31 g, 1.77 mmol) and Lawesson’s re-
agent (0.72 g, 1.77 mmol) in DME (50 mL) was stirred at 50 °C
for 12 h. The reaction mixture was concentrated in vacuo to give a
residue, which was purified on a silica-gel column using a mixture
of hexane and EtOAc (3:1 v/v) to give 41 as a yellow amorphous
material. Yield 68% (0.91 g). IR 3439, 3352, 3115, 3091, 3066,
1583 cm−1 1H NMR δ 1.43 (s, 9H, Boc), 1.46 (d, 3H, CH3, J =
.
6.3 Hz), 1.53 (s, 9H, OBut), 3.63 (d, 2H, thiazoline’s CH2, J = 9.2
Hz), 5.22 (t, 1H, thiazoline’s H, J = 9.2 Hz), 5.39 (s, 2H, Bn’s
CH2), 5.62–5.89 (m, 2H, BocNH, CHNH), 7.34–7.49 (m, 5H,
Bn’s Ph), 8.17 (d, 1H, pyridine’s H, J = 8.3 Hz), 8.20 (s, 1H, thia-
zole’s H), 8.34 (d, 1H, pyridine’s H, J = 8.3 Hz). Found: C,
59.50; H, 5.85; N, 8.90%. Calcd for C31H36N4O6S2: C, 59.61; H,
5.77; N, 8.97%.
3033, 2928, 1956, 1722, 1583, 1501 cm−1
.
1H NMR δ 0.01 and
t-Butyl (4S)-2-(2-{3-Benzyloxycarbonyl-2-[(1R)-t-butoxy-
carbonylaminoethyl]pyridin-6-yl}thiazol-4-yl)thiazole-4-car-
boxylate (45). A suspension of 44 (31 mg, 0.05 mmol) and
MnO2 (65 mg, 0.75 mmol) in toluene (1 mL) was stirred at room
temperature for 20 h. The MnO2 was filtered off and the filtrate
was concentrated in vacuo to give a residual substance, which was
purified on a silica-gel column using a mixture of hexane and
EtOAc (3:1 v/v) to give 45 as a colorless syrup. Yield 77% (24
mg). [α]D25 −44.7° (c 0.43, CHCl3). IR 3434, 3108, 2975, 2931,
0.04 (each s, 6H, TBS’s CH3 × 2), 0.88 (s, 9H, TBS’s But), 1.43
(s, 9H, Boc), 1.46 (d, 3H, CH3, J = 6.3 Hz), 1.52 (s, 9H, OBut),
4.17–4.19 (m, 2H, Ser’s β-H), 5.27–5.32 (m, 1H, Ser’s α-H), 5.41
(s, 2H, Bn’s CH2), 5.66–5.90 (m, 2H, NHBoc, CH3CH), 7.34–7.50
(m, 5H, Bn’s Ph), diastereomer 8.08 and 8.09 (each d, 1H, pyri-
dine’s H, J = each 8.3 Hz), diastereomer 8.33 and 8.34 (each d,
1H, pyridine’s H, J = 8.3 Hz), 8.56 (s, 1H, thiazole’s H), 9.96 (d,
1H, NH, J = 10.0 Hz). Found: C, 59.01; H, 6.88; N, 7.10%. Cal-
cd for C37H52N4O7 S2Si: C, 58.69; H, 6.92; N, 7.40%.
2361, 2342, 1718, 1583 cm−1 1H NMR δ 1.44 (s, 9H, Boc), 1.47
.
2-{3-Benzyloxycarbonyl-2-[(1R)- and (1S)-t-butoxycarbon-
ylaminoethyl]pyridin-6-yl}thiazole-4-thiocarbonyl-L-Ser-OBut
(42 and 43). To a solution of 41 (0.22 g, 0.29 mmol) in THF (30
mL) was added, with stirring, 2 M HCl (30 mL) at room tempera-
ture for a few minutes. Evaporation of THF gave a aqueous solu-
tion, which was extracted with EtOAc (20 mL × 3). The com-
bined extracts were washed with saturated NaHCO3 aqueous solu-
tion (20 mL × 2), and brine (10 mL × 2), and dried over anhy-
drous Na2SO4. Concentration in vacuo gave a residue, which was
purified on a silica-gel column using a mixture of hexane and
EtOAc (2:1 v/v) to give a mixture of diastereomeric isomers as a
crystalline material. The obtained crystals were again chromato-
graphed on a silica-gel column using a mixture of CHCl3 and ace-
tone (50:1 v/v) to give 42 from first eluate and 43 from last eluate
as yellow crystals. 42: Yield 41% (76 mg). Mp 174.5–176.5 °C.
[α]D25 −33.6° (c 1.00, CHCl3). IR 3392, 3302, 2981, 2934, 1725,
(d, 3H, CH3, J = 6.3 Hz), 1.64 (s, 9H, OBut), 5.40 (s, 2H, Bn’s
CH2), 5.64–5.92 (m, 2H, BocNH, CHNH), 7.34–7.50 (m, 5H,
Bn’s Ph), 8.09 (s, 1H, thiazole’s H), 8.18 (d, 1H, pyridine’s H, J =
8.3 Hz), 8.32 (s, 1H, thiazole’s H), 8.37 (d, 1H, pyridine’s H, J =
8.3 Hz). Found: C, 59.69; H, 5.74; N, 8.66%. Calcd for C31H34-
N4O6S2: C, 59.79; H, 5.50; N, 9.00%.
(4S)-2-(2-{3-Benzyloxycarbonyl-2-[(1S)-t-butoxycarbonyl-
aminoethyl]pyridin-6-yl}thiazol-4-yl)-4,5-dihydrothiazole-4-
carboxylate (46) and 2-(2-{3-Benzyloxycarbonyl-2-[(1S)-t-bu-
toxycarbonylaminoethyl]pyridin-6-yl}thiazol-4-yl)thiazole-4-
carboxylate (47). Similarly to the case of 42, a treatment of 43
(460 mg) with Ph3P (0.28 g) and DEAD (0.28 mL, 40% in tolu-
ene) was worked up to give a mixture of two chemical species,
which were easily separated on a silica-gel column using a mix-
ture of hexane and EtOAc (2:1 v/v) to give 46 from last eluate and
47 from first eluate as a colorless syrup. 46: Yield 19% (84 mg).
[α]D26 +47.1° (c 0.31, CHCl3). IR 3435, 3113, 2976, 2930, 2360,
1692, 1584, 1522 cm−1
.
1H NMR δ 1.43 (s, 9H, Boc), 1.45 (d,
3H, CH3, J = 6.6 Hz), 1.55 (s, 9H, OBut), 2.20 (t, 1H, OH, J = 6.3
1716, 1582 cm−1 1H NMR δ 1.43 (s, 9H, Boc), 1.46 (d, 3H, CH3,
.

1594 Bull. Chem. Soc. Jpn., 75, No. 7 (2002)
Main Structure of Cyclothiazomycin
J = 6.3 Hz), 1.53 (s, 9H, OBut), 3.63 (d, 2H, thiazoline’s CH2, J =
9.2 Hz), 5.23 (t, 1H, thiazoline’s CH, J = 9.2 Hz), 5.39 (s, 2H,
Bn’s CH2), 5.62–5.89 (m, 2H, BocNH, CHNH), 7.34–7.48 (m,
5H, Bn’s Ph), 8.17 (d, 1H, pyridine’s H, J = 8.3 Hz), 8.20 (s, 1H,
thiazole’s H), 8.34 (d, 1H, pyridine’s H, J = 8.3 Hz). 47: Yield
48% (211 mg). [α]D26 +54.0° (c 0.50, CHCl3). Found: C, 59.72; H,
5.63; N, 8.59%. Calcd for C31H36N4O6S2: C, 59.60; H, 5.77; N,
8.97%. The IR and 1H NMR spectra of 47 were completely iden-
tical with those of 45.
(S)-2-(1-Hydroxyethyl)pyridine [(S)-49]. According to the
method reported,14 the treatment of 2-acetylpyridine (2.50 g,
26.64 mmol) with dry Yeast (56 g) and D-glucose (64 g) in water
(500 mL) at room temperature for 24 h gave (S)-49 as a colorless
oil. Yield 48% (1.22 g). [α]D26 −55.5° (c 1.61, EtOH). {lit.14 [α]D
−55.5° (c 1.50, EtOH)}.
(R)-2-(1-Hydroxyethyl)pyridine [(R)-49]. A solution of (S)-
49 (1.56 mg, 1.27 mmol) and Ms-Cl (0.15 mL, 2.54 mmol) in the
presence of Et3N (0.53 mL, 3.81 mmol) in CHCl3 (20 mL) was
stirred at 0 °C for 30 min. The reaction mixture was washed with
brine (10 mL × 3), dried over anhydrous Na2SO4, and then con-
centrated in vacuo to give a residue. The residue was dissolved in
DMF (20 ml), to which was added AcONa (313 mg, 3.81 mmol)
and 15-crown-5-ether (18 µL, 0.13 mmol) at room temperature.
After stirring for 24 h, to the reaction mixture was added water (20
mL) and then the resulting solution was extracted with EtOAc (20
mL × 2). The combined extracts were washed with brine (20 mL
× 3), dried over anhydrous Na2SO4 and then concentrated in vac-
uo to give a residue. The obtained residue was purified on a silica-
gel column using a mixture of hexane and EtOAc (2:1 v/v) to give
a residual oil. The oil was again dissolved in a MeOH–water (20
mL, 2:1 v/v), to which was added, with stirring, K2CO3 (263 mg,
1.91 mmol) at 0 °C for 30 min. After stirring for 3 h at room tem-
perature, MeOH was evaporated and the residual aqueous layer
was extracted with EtOAc (20 mL × 5). The combined extracts
were washed once with brine (20 mL), dried over anhydrous
Na2SO4, and then concentrated in vacuo to give a residual oil. The
obtained oil was purified on a silica gel column using EtOAc to
give (R)-49 as a colorless oil. Yield 46% (72 mg). [α]D24 +56.2° (c
1.53, EtOH).
(R)-2-(1-t-Butoxycarbonylaminoethyl)pyridine [(R)-51].
A suspension of (R)-50 (166 mg, 1.12 mmol) and 10% Pd–C (10
mg) in EtOH (20 mL) under H2 gas stream was stirred at room
temperature for 30 min. The Pd–C was filtered off, the filtrate was
concentrated in vacuo to give a residue, which was dissolved in
CHCl3 (20 mL). To the resulting solution was added, with stir-
ring, Boc2O (367 mg, 1.68 mmol) and Et3N (0.91 mL, 1.34 mmol)
at 0 °C. After stirring for 3 h, the reaction mixture was washed
with brine (10 mL × 3) and dried over anhydrous Na2SO4. Con-
centration in vacuo gave a syrup, which was purified on a silica-
gel column using a mixture of hexane and EtOAc (2:1 v/v) to give
(R)-51 as a colorless syrup. Yield 81% (202 mg). [α]D25 +49.7° (c
1.01, MeOH). IR 3336, 2976, 2931, 1712, 1592, 1572, 1496,
1444 cm−1
.
1H NMR δ 1.44 (s, 9H, Boc), 1.37–1.52 (m, 3H,
CH3), 4.74–4.94 (m, 1H, CH), 5.64–5.78 (m, 1H, NH), 7.12–7.28
(m, 2H, pyridine’s H × 2), 7.64 (dt, 1H, pyridine’s H, J = 1.7, 7.8
Hz), 8.54 (d, 1H, pyridine’s H, J = 4.9 Hz). Found: C, 64.37; H,
7.97; N, 12.23%. Calcd for C12H18N2O2: C, 64.84; H, 8.16; N,
12.60%.
(S)-2-(1-t-Butoxycarbonylaminoethyl)pyridine
[(S)-51].
Similarly to the above case, (S)-51 was obtained from (S)-50.
Yield 78% (194 mg). [α]D25 −54.1° (c 0.98, MeOH). Found: C,
64.88; H, 8.05; N, 12.62%. Calcd for C12H18N2O2: C, 64.84; H,
8.16; N, 12.60%.
(S)-3-t-Butoxycarbonyl-2,2,5-trimethyloxazolidine-4-carbon-
yl-Gly-OMe (53). A solution of 52 (3.0 g, 12.92 mmol), DCC
(2.9 g, 14.21 mmol), HOSu (1.6 g, 14.21 mmol), and HCl•H-Gly-
OMe (1.15 g, 12.92 mmol) in CH2Cl2 (70 mL) was stirred at 0 °C
for 30 min and at room temperature for 6 h. The precipitated DCC
urea salt was filtered off, the filtrate was added to diethyl ether (80
mL). The resulting solution was washed with 10% citric acid (50
mL × 3), saturated NaHCO3 aqueous solution (50 mL × 3), and
brine (50 mL × 3) and then dried over anhydrous Na2SO4. Con-
centration in vacuo gave a residue, which was purified on a silica-
gel column using a mixture of hexane and EtOAc (1:1 v/v) to give
colorless crystals. Recrystallization from a hexane–EtOAc gave
53 as colorless needles. Yield 70% (2.64 g). Mp 135–137 °C.
[α]D23 −4.40° (c 1.80, MeOH). IR 3328, 2980, 1755, 1710, 1671,
1566 cm−1 1H NMR δ 1.38 (d, 3H, Thr’s CH3, J = 5.7 Hz), 1.44
.
(R)-2-(1-Azidoethyl)pyridine [(R)-50]. A solution of (S)-49
(185 mg, 1.50 mmol) and Ms-Cl (0.23 mL, 3.00 mmol) in the
presence of Et3N (0.62 mL, 4.50 mmol) in CHCl3 (20 mL) was
stirred at 0 °C for 30 min. The reaction mixture was washed with
brine (10 mL × 3), dried over anhydrous Na2SO4 and then con-
centrated in vacuo to give a residual substance. The residue was
dissolved in DMF (20 mL) and treated with NaN3 (293 mg, 450
mmol) at room temperature. After stirring overnight, the reaction
mixture was diluted with water (20 mL) and the resulting solution
was extracted with EtOAc (20 mL × 2). The combined extracts
were washed with brine (20 mL × 3) and dried over anhydrous
Na2SO4. Concentration in vacuo gave a residual oil, which was
purified on a silica-gel column using a mixture of hexane and
EtOAc (2:1 v/v) to give (R)-50 as a colorless oil. Yield 75% (166
mg). [α]D25 +61.1° (c 1.09, MeOH). IR 2981, 2933, 2110, 1592,
(s, 9H, Boc), 1.61 and 1.63 (each s, 6H, Isop’s CH3 × 2), 3.77 (s,
3H, OMe), 3.75–3.78 (m, 1H, Thr’s β-H), 4.08 (d, 2H, Gly’s CH2,
J = 5.1 Hz), 4.05–4.11 (m, 1H, Thr’s α-H), 6.38–6.70 (br d, 1H,
Gly’s NH). Found: C, 44.07; H, 9.54; N, 9.98%. Calcd for
C17H26N2O6: C, 44.43; H, 9.69; N, 10.36%.
(S)-3-t-Butoxycarbonyl-2,2,5-trimethyloxazolidine-4-carbon-
yl-Gly-OH (54). To a solution of 53 (205 mg, 0.60 mmol) in
water–dioxane (30 mL, 1:1 v/v) was added 1 M LiOH (0.90 mL,
0.90 mmol) at 0 °C. After stirring for 30 min, the reaction mixture
was washed with diethyl ether (10 mL × 3), and the resulting
aqueous solution was acidified to pH 4 with citric acid hydrate and
then extracted with EtOAc (10 mL × 3). The combined extracts
were dried over anhydrous Na2SO4. Concentration in vacuo gave
colorless crystals, which were recrystallized from a hexane–
EtOAc to give 54 as colorless needles. Yield 98% (194 mg). Mp
175–176 °C. [α]D24 +180.8° (c 0.1, MeOH). IR 3289, 2980, 2932,
1473, 1436 cm−1 1H NMR δ 1.61 (d, 3H, CH3, J = 6.8 Hz), 4.68
.
(q, 1H, CH, J = 6.8 Hz), 7.18–7.30 (m, 1H, pyridine’s H), 7.35 (d,
1H, pyridine’s H, J = 7.8 Hz), 7.72 (dt, 1H, pyridine’s H, J = 1.7,
7.8 Hz), 8.59 (d, 1H, pyridine’s H, J = 4.9 Hz).
1749, 1668, 1578 cm−1 1H NMR δ 1.40 (d, 3H, Thr’s CH3, J =
.
6.1 Hz), 1.44 (s, 9H, Boc), 1.59 and 1.62 (each s, 6H, Isop’s CH3
× 2), 3.89 (d, 1H, Thr’s β-H, J = 7.6 Hz), 4.08–4.11 (m, 2H,
Gly’s CH2), 4.23–4.18 (m, 1H, Thr’s α-H), 6.68–6.95 (br s, 1H,
Gly’s NH), 8.46–8.70 (br s, 1H, COOH). Found: C, 53.05; H,
7.55; N, 8.53%. Calcd for C14H24N2O6: C, 53.15; H, 7.65; N,
(S)-2-(1-Azidoethyl)pyridine [(S)-50].
Similarly to the
above case, (R)-50 was obtained from (R)-49. Yield 72% (160
mg). [α]D24 −50.4° (c 1.10, MeOH).

C. Shin et al.
Bull. Chem. Soc. Jpn., 75, No. 7 (2002) 1595
8.86%.
N, 9.68%. Calcd for C19H31N3O7: C, 55.19; H, 7.56; N, 10.16%.
(S)-3-t-Butoxycarbonyl-2,2,5-trimethyloxazolidine-4-carbon-
yl-Gly-L-Thr(TBS)-OMe (55). To a solution of 54 (4.84 g,
14.22 mmol) in DMF (50 mL) were added, with stirring, HOBt
(2.88 g, 21.33 mmol) at 0 °C for 10 min and then DCC (3.95 g,
19.13 mmol). After stirring for 30 min at 0 °C, H-L-Thr(TBS)-
OMe (3.52 g, 14.22 mmol) was added, and the resulting solution
was further stirred at room temperature for 6 h. The precipitated
DCC urea salt was filtered off and the filtrate was added to water
(50 mL). The solution was extracted with EtOAc (40 mL × 3)
and the combined extracts were washed with 10% citric acid (30
mL × 2), a saturated NaHCO3 aqueous solution (30 mL × 2), and
brine (30 mL × 2), and then dried over anhydrous Na2SO4. Con-
centration in vacuo gave a residue, which was purified on a silica-
gel column using a mixture of hexane and EtOAc (2:1 v/v) to give
55 as a colorless syrup. Yield 96% (7.45 g). [α]D28 −51.4° (c 0.86,
(S)-3-t-Butoxycarbonyl-2,2,5-trimethyloxazolidine-4-carbon-
∆
yl-Gly-(Z)- Abu-OH (58). To a solution of 57 (1.50 g, 3.63
mmol) in water–dioxane (100 mL, 1:1 v/v) was added, with stir-
ring, 1 M LiOH (5.45 mL, 5.45 mmol) at 0 °C. After stirring for
30 min and at room temperature for 6 h, the reaction mixture was
washed with diethyl ether (30 mL × 2) and acidified to pH 4 with
citric acid hydrate. The resulting solution was extracted with
EtOAc (30 mL × 3) and the combined extracts were washed with
brine (20 mL × 2), and then dried over anhydrous Na2SO4. Con-
centration in vacuo gave a crystalline residue, which was recrys-
tallized from a hexane–EtOAc to give 58 as colorless needles.
Yield 98% (1.43 g). Mp 174–175 °C. [α]D26 −17.4° (c 1.01,
MeOH). IR 3281, 3058, 2981, 2936, 2360, 2342, 1707, 1669,
1528 cm−1 1H NMR (DMSO-d6) δ 1.31 (d, 3H, Thr’s CH3, J =
.
5.9 Hz), 1.36 (s, 9H, Boc), each 1.52 (each s, 6H, Isop’s CH3 × 2),
1.67 (d, 3H, ∆Abu’s CH3, J = 7.3 Hz), 3.75–4.10 (m, 4H, Thr’s α-
H, Thr’s β-H, Gly’s CH2), 6.58 (q, 1H, ∆Abu’s H, J = 7.3 Hz),
8.15–8.23 (br s, 1H, Gly’s NH), 8.70–8.59 (br s, 1H, ∆Abu’s NH),
12.07–12.21 (br s, 1H, COOH). Found: C, 54.28; H, 7.46; N,
10.20%. Calcd for C18H29N3O7: C, 54.13; H, 7.32; N, 10.52%.
(S)-3-t-Butoxycarbonyl-2,2,5-trimethyloxazolidine-4-carbon-
MeOH). IR 3376, 3334, 2920, 2890, 2854, 1662, 1503 cm−1 1H
.
NMR (DMSO-d6) δ 0.01 and 0.05 (each s, 6H, TBS’s CH3 × 2),
0.86 (s, 9H, TBS’s But), 1.11 (d, 3H, Thr’s CH3, J = 6.3 Hz), 1.31
(d, 3H, Thr’s CH3, J = 5.9 Hz), 1.36 (s, 9H, Boc), 1.51 and 1.52
(each s, 6H, Isop’s CH3 × 2), 3.65 (s, 3H, OCH3), 3.65–3.85 (m,
2H, Gly’s CH2), 3.98–4.19 (m, 2H, Thr’s α-H, Thr’s β-H), 4.31–
4.36 (m, 1H, Thr’s β-H), 4.43–4.47 (m, 1H, Thr’s α-H), 7.44 (d,
1H, Thr’s NH, J = 8.9 Hz), 8.19–8.23 (br s, 1H, Gly’s NH).
Found: C, 55.02; H, 8.97; N, 7.56%. Calcd for C25H47N3O8Si: C,
55.02; H, 8.68; N, 7.70%.
∆
yl-Gly-(Z)- Abu-L-Pro-OMe (59). To a solution of 58 (1.38 g,
3.45 mmol) in DMF (50 mL) were added, with stirring, HOBt
(0.70 g, 5.18 mmol) at 0 °C for 10 min and DCC (0.89 g, 4.31
mmol). After stirring for 30 min, H-Pro-OMe (0.53 g, 4.14 mmol)
was added to the resulting solution, which was then further stirred
at 0 °C for 30 min and at room temperature for 6 h. The precipi-
tated DCC urea salt was filtered off, the filtrate was added to water
(60 mL), and the solution was extracted with EtOAc (30 mL × 3).
The combined extracts were washed with 10% citric acid (30 mL
× 2), saturated NaHCO3 aqueous solution (30 mL × 3), and brine
(30 mL × 3) and then dried over anhydrous Na2SO4. Concentra-
tion in vacuo gave a residue, which was purified on a silica-gel
column using a mixture of hexane and acetone (1:1 v/v) to give 59
as a colorless amorphous. Yield 71% (1.25 g). [α]D24 −41.4° (c
(S)-3-t-Butoxycarbonyl-2,2,5-trimethyloxazolidine-4-carbon-
yl-Gly-L-Thr-OMe (56). A solution of 55 (3.48 g, 6.38 mmol)
in THF (80 mL) in the presence of TBAF (9.57 mL in 1 M THF,
9.57 mmol) was stirred at 0 °C for 5 min and then at room temper-
ature for 30 min. The reaction mixture was concentrated in vacuo
to give a residue, which was purified on a silica-gel column using
EtOAc to give 56 as a colorless syrup. Yield 83% (2.28 g). [α]D23
−44.3° (c 0.94, MeOH). IR 3338, 3079, 2981, 2937, 1748, 1666,
1534 cm−1 1H NMR δ 1.22 (d, 3H, Thr’s CH3, J = 6.3 Hz), 1.40
.
(d, 3H, Thr’s CH3, J = 5.9 Hz), 1.45 (s, 9H, Boc), 1.61 (s, 6H,
Isop’s CH3 × 2), 3.59–3.76 (br s, 1H, OH), 3.76 (s, 3H, OCH3),
3.80–3.83 (m, 1H, Thr’s α-H), 4.16–4.24 (m, 1H, Thr’s β-H),
4.34–4.41 (m, 1H, Thr’s β-H), 4.61 (dd, 1H, Thr’s β-H, J = each
9.2 Hz), 7.00–7.24 (br s, 2H, NH × 2). Found: C, 52.07; H, 7.75;
N, 9.14%. Calcd for C19H33N3O8•0.5H2O: C, 51.81; H, 7.78; N,
9.54%.
0.4, MeOH). IR 3310, 2980, 1877, 1746, 1671, 1617 cm−1 1H
.
NMR (DMSO-d6) δ 1.29 (d, 3H, Thr’s CH3, J = 5.5 Hz), 1.35 (s,
9H, Boc), 1.50 and 1.51 (each s, 6H, Isop’s CH3 × 2), 1.65 (d, 3H,
∆Abu’s CH3, J = 6.7 Hz), 1.75–1.92 (m, 3H, Pro’s H and H2),
2.08–2.15 (m, 1H, Pro’s H), 3.38–3.43 (br s, 1H, Pro’s H), 3.56–
3.62 (m, 1H, Pro’s H), 3.62 (s, 3H, OCH3), 3.72–4.09 (m, 4H,
Thr’s α-H, Thr’s β-H, and Gly’s CH2), 4.29–4.45 (br s, 1H, Pro’s
H), 5.45–5.69 (br s, 1H, ∆Abu’s H), 8.10–8.20 (br s, 1H, Gly’s
NH), 8.94–9.12 (br s, 1H, ∆Abu’s NH). Found: C, 56.98; H, 7.11;
N, 10.83%. Calcd for C24H38N4O8: C, 56.75; H, 7.54; N, 11.03%.
(S)-3-t-Butoxycarbonyl-2,2,5-trimethyloxazolidine-4-carbon-
(S)-3-t-Butoxycarbonyl-2,2,5-trimethyloxazolidine-4-carbon-
∆
yl-Gly-(Z)- Abu-OMe (57). A solution of 56 (1.16 g, 2.69
mmol) and Ms-Cl (0.25 mL, 3.23 mmol) in CHCl3 (50 mL) in the
presence of Et3N (0.75 mL, 5.38 mmol) was stirred at 0 °C for 30
min. To the resulting solution was further added DBU (4.02 mL,
26.90 mmol). After stirring at 0 °C for 10 min and at room tem-
perature for 6 h, the reaction mixture was washed with 10% citric
acid (20 mL × 2), saturated NaHCO3 aqueous solution (20 mL ×
3), and brine (20 mL × 2) and the dried over anhydrous Na2SO4.
Concentration in vacuo gave a residue, which was purified on a
silica-gel column using EtOAc to give a crystalline residue. Re-
crystallization from a hexane–EtOAc gave 57 as colorless fibrous.
Yield 89% (0.99 g). Mp 141–142 °C. [α]D28 −15.6° (c 0.87,
∆
yl-Gly-(Z)- Abu-L-Pro-OH [(P)-6]. A solution of 59 (1.25 g,
2.45 mmol) and 1 M LiOH (3.68 mL) in a mixture of H2O–diox-
ane (30 mL, 1:1 v/v) was stirred at 0 °C for 10 min and then at
room temperature for 1 h. The reaction mixture was washed with
diethyl ether (30 mL × 3). The aqueous layer was acidified with
citric acid hydrate to pH 4 and then extracted with EtOAc (30 mL
× 3). The combined extracts were washed with brine (30 mL ×
3) and dried over anhydrous Na2SO4. Concentration in vacuo
gave a colorless syrup (P)-6, quantitatively, which was used to the
reaction with (P)-3.
The Protected Fragment A-B [(P)-3]. To a solution of 44
(78 mg, 0.13 mmol) in CHCl3 (2 mL) was added TFA (3 mL) at
room temperature. After stirring for 5 h, the reaction mixture was
concentrated in vacuo to give a residue, which was dissolved in
MeOH). IR 3286, 2968, 1701, 1641, 1521 cm−1 1H NMR δ 1.35
.
(d, 3H, Thr’s CH3, J = 5.9 Hz), 1.37 (s, 9H, Boc), 1.58 (s, 6H,
Isop’s CH3 × 2), 1.74 (d, 3H, ∆Abu’s CH3, J = 7.1 Hz), 3.71 (s,
3H, OMe), 3.76–4.40 (m, 4H, Thr’s α-H, Thr’s β-H, Gly’s CH2),
6.84 (q, 1H, ∆Abu’s H, J = 7.1 Hz), 6.92–7.20 (br s, 1H, Gly’s
NH), 8.29–8.64 (br s, 1H, ∆Abu’s NH). Found: C, 55.32; H, 7.80;

1596 Bull. Chem. Soc. Jpn., 75, No. 7 (2002)
Main Structure of Cyclothiazomycin
CHCl3 (5 mL). The resulting solution was stirred with Et3N (30
µL, 0.20 mmol) and Boc2O (42 mg, 0.20 mmol) at 0 °C for 30 min
and at room temperature for 5 h. The reaction mixture was mixed
with 10% citric acid (5 mL). The organic layer was washed with
brine (5 mL) and dried over anhydrous Na2SO4. Concentration in
vacuo gave a colorless syrup 60, which was dissolved in DMF (10
mL). To the resultant solution was added (P)-4, derived by depro-
tection of the Boc group of 19 (92 mg, 0.13 mmol) with TFA–
CHCl3 (10 mL, 2:3 v/v) at room temperature for 30 min, and then
N,N-diisopropylethylamine (40 µL, 0.23 mmol) and BOP (75 mg,
0.17 mmol) at 0 °C. After stirring for 30 min and at room temper-
ature for 4 h, the reaction mixture was mixed with water (10 mL)
and extracted with EtOAc (10 mL × 3). The combined extracts
were washed with 10% citric acid (10 mL × 2), saturated
NaHCO3 aqueous solution (10 mL × 2), brine (10 mL × 2), and
then dried over anhydrous Na2SO4. Concentration in vacuo gave a
residual syrup, which was purified on a silica-gel column using a
mixture of hexane and EtOAc (1:1 v/v) to give (P)-3 as a colorless
syrup. Yield 58% (87 mg) from 44 in three steps. [α]D22 +11.1° (c
0.27, CHCl3). IR 3389, 2929, 2333, 1715, 1684, 1582, 1489,
This work was supported in part by a Grant-in-Aid for Sci-
entific Research No. 12640529 from the Ministry of Educa-
tion, Science, Sports and Culture and by “High-Tech Research
Project” from the Ministy of Education, Culture, Sports, Sci-
ence and Technology.
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1438 cm−1 1H NMR δ diastereomer 0.93 and 0.95 (each s, 9H,
.
TPS’s But), 1.29–1.65 (m, 12H, Boc, CH3CH), 3.62–3.85 (m, 4H,
thiazoline’s CH2 × 2), diastereomer 3.86 (each s, 3H, OCH3),
3.94–4.14 (m, 2H, CH2O), 4.37 (d, 1H, CHCH2O, J = 10.5 Hz),
5.28–5.39 (m, 2H, thiazoline’s H × 2), 5.40 (s, 2H, Bn’s CH2),
5.46–5.54 (m, 1H, CONH), 5.63–5.85 (m, 2H, BocNH, CH3CH),
7.20–7.60 (m, 15H, TPS’s Ph × 2, Bn’s Ph), 7.98–8.10 (m, 3H,
thiazole’s H × 3), 8.15 and 8.34 (each d, 2H, pyridine’s H, J = 7.5
Hz). Found: C, 58.00; H, 4.99; N, 9.88%. Calcd for C56H58N8O8-
S5Si: C, 58.01; H, 5.04; N, 9.66%.
3
a) P. Brooks, A. T. Fuller, and J. Walker, J. Chem. Soc.,
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C. Shin, K. Okumura, M. Shigekuni, and Y. Nakamura,
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5
K. Okumura, A. Ito, D. Yoshioka, and C. Shin, Heterocy-
The Protected Fragment A-B-C [(P)-2]. A solution of (P)-3
(51 mg, 0.04 mmol) and TFA (1 mL) in CHCl3 (1.5 mL) was
stirred at room temperature for 30 min. The reaction mixture was
concentrated in vacuo to give a residual syrup, which was dis-
solved in DMF (5 mL). To the resulting solution were added, with
stirring, (P)-6 (44 mg, 0.08 mmol), N,N-diisopropylethylamine
(14 µL, 0.07 mmol), and BOP (25 mg, 0.05 mmol) at 0 °C. After
stirring for 30 min and at room temperature for 12 h, the reaction
mixture was mixed with water (5 mL) and the resulting solution
was extracted with EtOAc (10 mL × 2). The combined extracts
were washed with 10% citric acid (5 mL × 2), saturated NaHCO3
aqueous solution (5 mL × 2), and brine (5 mL × 2), and then
dried over anhydrous Na2SO4. Concentration in vacuo gave a syr-
up, which was purified on a silica-gel column using a mixture of
CHCl3 and MeOH (20:1 v/v) to give (P)-2 as a pale-yellow syrup.
Yield 76% (47 mg). [α]D22 −38.8° (c 0.50, MeOH). IR 3310,
2973, 2931, 1677, 1507, 1437 cm−l. 1H NMR (DMSO-d6, 80 °C)
δ 0.90–0.98 (m, 9H, TPS’s But), 1.28–1.55 (m, 15H, Thr’s CH3,
∆Abu’s CH3, pyridine-CHCH3, Isop’s CH3 × 2), 1.37 (s, 9H,
Boc), 1.67–1.80 (m, 2H, Pro’s H2), 1.83–1.93 (m, 1H, Pro’s H),
1.97–2.07 (m, 1H, Pro’s H), 3.32–3.44 (m, 1H, Pro’s H), diastere-
omer 3.77 and 3.79 (each s, 3H, OCH3), 3.56–4.27 (m, 11H, Pro’s
H2, thiazoline’s CH2 × 2, Thr’s β-H, Gly’s CH2, CHCH2O), 5.45
(s, 2H, Bn’s CH2), 5.36–5.53 (m, 4H, Pro’s H, CHCH2O, thiazo-
line’s CH × 2), 5.71–5.84 (m, 2H, ∆Abu’s olefin-H, pyridine-
CHCH3), 7.32–7.62 (m, 15H, TPS’s Ph × 2, Bn’s Ph), 8.03–8.42
(m, 7H, pyridine-CHNH, pyridine’s H × 2, thiazole’s H × 3,
Gly’s NH), 9.05 (br s, 1H, ∆Abu’s NH). Found: C, 57.95; H, 5.67:
N, 10.49%. Calcd for C74H84N12O13S5Si: C, 57.79; H, 5.51; N,
10.93%.
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