Conversion of nocathiacin I to nocathiacin acid by a mild and selective cleavage of dehydroalanine

Article abstract of DOI:10.1021/jo071115p

(Chemical Equation Presented) Thiazolyl peptide antibiotic nocathiacin I (1) was converted to nocathiacin acid (4) in high yield by treatment with trifluoroacetic anhydride and pyridine in THF at room temperature. Two equipotent water-soluble amide analog

Full text of DOI:10.1021/jo071115p

aureus and shows in vivo efficacy in a systemic S. aureus
infection mouse model,5 its poor aqueous solubility precludes
its development as a hospital i.V. drug for serious infections.
However, with its novel structure and high intrinsic activity,
nocathiacin I provides a promising lead for the development of
new antibacterial agents with broad spectrum efficacy against
resistant pathogens with minimal risk of cross-resistance to
currently marketed agents.
Conversion of Nocathiacin I to Nocathiacin Acid
by a Mild and Selective Cleavage of
Dehydroalanine
Libo Xu,* Amy K. Farthing, Yao-Jun Shi,
Peter T. Meinke, and Kun Liu
Merck Research Laboratories, P.O. Box 2000,
Rahway, New Jersey 07065
libo_xu@merck.com
ReceiVed May 25, 2007
Thiazolyl peptide antibiotic nocathiacin I (1) was converted
to nocathiacin acid (4) in high yield by treatment with
trifluoroacetic anhydride and pyridine in THF at room
temperature. Two equipotent water-soluble amide analogues
of nocathiacin I were readily prepared from this important
and versatile carboxylic acid intermediate under mild peptide
coupling conditions. The present method is useful for
chemical derivatization of complex natural products that
contain C-terminal dehydroalanine.
FIGURE 1. Structures of nocathiacins I and IV.
Several approaches have been applied to 1 and its analogues
to obtain compounds with increased aqueous solubility.6-10 As
part of our effort to generate water-soluble analogues while
maintaining antibacterial activity, we intended to substitute the
dehydroalanine side chain with polar, water-solubilizing amides.
Although a similar approach has been described in the literature,8
which involved condensation of nocathiacin IV (2) with
glycoaldehyde and reductive amination of the Amadori rear-
ranged intermediate, products from this sequence of transforma-
Nocathiacins are a group of thiazolyl peptide antibiotics
recently discovered and isolated from the fermentation broth
of Norcadia sp.1-2 and fungus Amicolaptosis sp.3 Nocathiacin
I (1), the most abundant member of the family, displays potent
in vitro antibacterial activity4 against a variety of Gram-positive
bacteria, including methicillin-resistant Staphylococcus aureus
(MRSA), methicillin-resistant Enterococcus faecium (MREF),
vancomycin-resistant Enterococci (VRE), and penicillin-resistant
Streptococcus pneumoniae (PRSP). Similar to other thiazolyl
peptide antibiotics, nocathiacins function through inhibition of
bacterial protein synthesis by binding to the 23S rRNA of the
50S ribosomal subunit at the L11 binding domain. Though
nocathiacin I exhibits desirable bactericidal activity against S.
(5) Yang, H.; Chaniewski, S.; Clark, J.; Ferraro, C.; Gali, V.; Lamb, L.;
Medina, I. Abstracts of Papers, 43rd Annual ICAAC Meeting, Chicago,
IL, Sept 14-17; American Society for Microbiology: Washington, DC,
2003; B-319.
(6) Regueiro-Ren, A.; Naidu, B. N.; Zheng, X.; Hudyma, T. W.;
Connolly, T. P.; Matiskella, J. D.; Zhang, Y.; Kim, O. K.; Sorenson, M.
E.; Pucci, M.; Clark, J.; Bronson, J. J.; Ueda, Y. Bioorg. Med. Chem. Lett.
2004, 14, 171-175.
(7) Naidu, B. N.; Sorenson, M. E.; Zhang, Y.; Kim, O. K.; Matiskella,
J. D.; Wichtowski, J. A.; Connolly, T. P.; Li, W.; Lam, K. S.; Bronson, J.
J.; Pucci, M. J.; Clark, J. M.; Ueda, Y. Bioorg. Med. Chem. Lett. 2004, 14,
5573-5577.
(8) Hrnciar, P.; Ueda, Y.; Huang, S.; Leet, J. E.; Bronson, J. J. J. Org.
Chem. 2002, 67, 8789-8793.
(9) Naidu, B. N.; Sorenson, M. E.; Matiskella, J. D.; Wichtowski, J. A.;
Li, W.; Sauaker, J. B.; Zhang, Y.; Connolly, T. P.; Lam, K. S.; Bronson, J.
J.; Pucci, M. J.; Yang, H.; Ueda, Y. Bioorg. Med. Chem. Lett. 2006, 16,
3545-3549.
(10) Naidu, B. N.; Li, W.; Sorenson, M. E.; Connolly, T. P.; Wichtowski,
J. A.; Zhang, Y.; Kim, O. K.; Matiskella, J. D.; Lam, K. S.; Bronson, J. J.;
Ueda, Y. Tetrahedron Lett. 2004, 45, 1059-1063.
(1) Li, W.; Leet, J. E.; Ax, H. A.; Gustavson, D. R.; Brown, D. M.;
Turner, L.; Brown, K.; Clark, J.; Yang, H.; Fung-Tomc, J.; Lam, K. S. J.
Antibiot. 2003, 56, 226-231.
(2) Leet, J. E.; Li, W.; Ax, H. A.; Matson, J. A.; Huang, S.; Huang, R.;
Cantone, J. L.; Drexler, D.; Dalterio, R.; Lam, K. S. J. Antibiot. 2003, 56,
232-242.
(3) Sasaki, T.; Otani, T.; Matsumoto, H.; Unemi, N.; Hamada, M.;
Takeuchi, T.; Hori, M. J. Antibiot. 1998, 51, 715-721.
(4) Pucci, M. J.; Bronson, J. J.; Barrett, J. F.; DenBleyker, K. L.; Discotto,
L. F.; Fung-Tomc, J. C.; Ueda, Y. Antimicrob. Agents Chemother. 2004,
48, 3697-3701.
10.1021/jo071115p CCC: $37.00 © 2007 American Chemical Society
Published on Web 08/18/2007
J. Org. Chem. 2007, 72, 7447-7450
7447

SCHEME 1. Conversion of 1 to 4 and Synthesis of Water-Soluble Amides 5 and 6
tions are limited to only aminoethyl amides. Other literature
precedents on chemical modifications of the dehydroalanine unit
of 1 also suffer from lengthy sequence or limited scope of
structural features that can be installed.9,10 We envisioned a more
straightforward strategy that involves the formation of carboxylic
acid 4, which can serve as a versatile intermediate to be
transformed to a variety of amide analogues under mild and
selective peptide coupling conditions.
The complex structure and chemical instability of nocathiacins
present a formidable challenge for their synthetic modifications.
Similar to the disappointing results reported in the literature,8
our initial attempts to cleave the dehydroalanine moiety directly
from 1 or hydrolyze the primary amide bond in 2 failed. Instead
of the desired carboxylic acid 4, complete decomposition of
nocathiacin I or IV was observed under a variety of mild amide
bond cleavage conditions, including acidic, basic, and oxidative
conditions.11-17 It became clear that a novel and mild method
would need to be developed to achieve the desired transforma-
tion from 1 to 4.
or acetonitrile at room temperature, followed by quenching with
water (Scheme 1). LC-MS analyses of the reaction mixture
revealed that under these conditions, 1 is first converted to 3,
which is then gradually transformed to 4. The reaction can be
stopped at the nitrile stage by using less TFAA or running the
reaction at 0 °C. When isolated 3 was subjected to the same
reaction conditions (TFAA and pyridine in THF), it was
smoothly transformed to 4. Under optimal conditions (5 equiv
of TFAA, 10 equiv of pyridine, 0.01-0.1 M concentration), 4
was formed almost quantitatively by LC-MS and isolated in
50-80% yield by preparative HPLC.
It should be noted that acid 4 formed in the reaction was
mono-trifluoroacetylated based on LC-MS analysis. However,
the trifluoroacetyl group can be easily removed with aqueous
sodium bicarbonate or under other mild hydrolytic conditions.
The precise point of acylation was not established, but prelimi-
nary studies exclude the indole N-OH, pyridyl OH, or sugar
OH as the acylation site because both dimethyl nocathiacin I,6
which lacks indole N-OH and pyridyl OH, and thiazomycin,18
which lacks the sugar OH, form mono-trifluoroacetylated acid
upon treatment with TFAA/pyridine.
We first observed the formation of nocathiacin acid 4 in trace
amount during the synthesis of nitrile 3 by treatment of 1 with
trifluoroacetic anhydride (TFAA) in pyridine. After carefully
monitoring the reaction process and surveying different reaction
conditions, we discovered that 4 can be formed as the major
product by reacting 1 with excess TFAA and pyridine in THF
Mechanistic studies of the newly discovered transformation
using 1 were complicated by its complex structure and limited
supply, therefore a model compound (7) bearing the dehy-
droalanine unit was synthesized. Compound 7 was prepared in
three steps from known N-(tert-butoxycarbonyl)-L-(Se)-phe-
nylselenocysteine19 by the method developed by van der Donk
in which the dehydroalanine unit was formed by oxidative
elimination of phenylselenocysteine. When compound 7 was
(11) Flynn, D. L.; Zelle, R. E.; Grieco, P. A. J. Org. Chem. 1983, 48,
2424-2426.
(12) Lee, S. D.; Brook, M. A.; Chan, T. H. Tetrahedron Lett. 1983, 24,
1569-1572.
(13) Gassman, P. G.; Hodgwon, P. K. G.; Balcunis, R. J. J. Am. Chem.
Soc. 1976, 98, 1275-1276.
(14) Pascal, R.; Sola, R. Tetrahedron Lett. 1998, 39, 5031-5034.
(15) Tsunoda, T.; Sasaki, O.; Itoˆ, S. Tetrahedron Lett. 1990, 31, 731-
734.
(18) Jayasuriya, H.; Herath, K.; Ondeyka, J. G.; Zhang, C.; Zink, D. L.;
Brower, M.; Gailliot, F. P.; Greene, J.; Birdsall, G.; Venugopal, J.; Ushio,
M.; Burgess, B.; Russotti, G.; Walker, A.; Hesse, M.; Seeley, A.; Junker,
B.; Connors, N.; Salazar, O.; Genilloud, O.; Liu, K.; Masurekar, P.; Barrett,
J. F.; Singh, S. B. J. Antibiot. Submitted for publication.
(19) Okeley, N. M.; Zhu, Y.; van der Donk, W. A. Org. Lett. 2000, 2,
3603-3606.
(16) Kelly, T. R.; Jagoe, C. T.; Gu, Z. Tetrahedron Lett. 1991, 32, 4263-
4266.
(17) Evans, D. A.; Carter, P. H.; Dinsmore, C. J.; Barrow, J. C.; Katz,
J. L.; Kung, D. W. Tetrahedron Lett. 1997, 38, 4535-4538.
7448 J. Org. Chem., Vol. 72, No. 19, 2007

SCHEME 2. Proposed Mechanism for Dehydroalanine
Cleavage
antibacterial activity of 5 and 6 is comparable to that of 1, with
the minimum inhibitory concentrations (MICs) against S. aureus
of 0.0075 and 0.06 µg/mL, respectively. In comparison, 1 shows
solubility of 0.34 mg/mL at pH 4.0 and MIC against S. aureus
of 0.007 µg/mL.8
In summary, we have developed a mild and efficient method
to convert thiazolyl peptide antibiotic 1 to nocathiacin acid (4)
through a facile cleavage of dehydroalanine using trifluoroacetic
anhydride and pyridine in THF. We also demonstrated the
synthetic utility of this highly desirable intermediate by the
convenient synthesis of two novel water-soluble amide ana-
logues (5 and 6) of nocathiacin I in good yields. More synthetic
applications of 4 in the preparation of water-soluble amides,
esters, thioesters, and their biological activities will be the
subject of a separate publication. The C-terminal dehydroalanine
motif is found in a number of natural products, such as
nosiheptide, glycothiohexide, siomycins, sulfomycins, promo-
thiocin,21-24 and thiazomycin.18 The method described herein
was already successfully applied to thiazomycin, a new member
of the nocathiacin family, and generated many useful analogues
(data not shown). It can potentially be applied to other antibiotics
mentioned above and facilitate their derivitization under mild
conditions compatible with their structural complexity and
chemical sensitivity.
treated with excess TFAA/pyridine in THF, immediate forma-
tion of nitrile 8 was observed, and the corresponding acid 12
was formed quantitatively within 2 h upon quenching with
water. In the absence of pyridine, nitrile 8 was still formed after
the addition of TFAA, but no acid formation was detected even
after 24 h. Substituting pyridine with N,N-diisopropylethylamine
also resulted in complete conversion of 7 to 8, but again no
acid formation was observed. Thus it seems that pyridine is
mechanistically involved in the transformation. We postulate
that the reaction proceeds through N-acylation of 8 to form the
reactive intermediate 9, followed by nucleophilic attack by
pyridine to generate the acyl pyridinium species 10 (Scheme
2), which yields acid 12 upon quenching with water. If the
reaction mixture is quenched with methanol instead, the
corresponding methyl ester is formed, presumably through the
same reactive intermediate 10. To further support the above
mechanistic hypothesis, acrylonitrile 11 was isolated from the
reaction mixture and its structure was confirmed by spectro-
scopic analyses. A brief survey of the same reaction on
structurally related substrates suggests that this reaction is
specific for the degradative cleavage of dehydroalanine amides
or esters. The corresponding saturated compound containing
alanine did not yield any 2-phenyl-1,3-thiazo-4-carboxylic acid
(12) under the same conditions.
To demonstrate the synthetic utility of this important inter-
mediate, carboxylic acid 4 was converted under mild and
selective conditions to a variety of amide and ester derivatives
containing various water-solubilizing groups, as exemplified by
5 and 6 (Scheme 1). Standard peptide coupling reactions (PyBop
or EDC/HOBt in DMF) between 4 and N-(3-aminopropyl)-
morpholine or 1-methylpiperazine afforded amides 5 and 6,
respectively, in good isolated yield.20 Both 5 and 6 retained
potent antibacterial activity and showed much improved solubil-
ity relative to nocathiacin I at acidic pH. The solubility of these
two compounds as their TFA salts is greater than 10 mg/mL in
water containing 5% dextrose with a pH of 4.0. The in vitro
Experimental Section
Nocathiacin Acid (4). To a solution of nocathiacin I (1, 100
mg, 0.07 mmol) in tetrahydrofuran (4 mL) at 0 °C was added
pyridine (0.11 mL, 1.4 mmol) and trifluoroacetic anhydride (0.1
mL, 0.7 mmol) slowly. After addition, the reaction mixture was
allowed to warm to room temperature and stirring was continued
for 6 h. A second portion of pyridine (0.05 mL) and TFAA (0.05
mL) were added, and after 4 h the reaction was quenched by
addition of a small amount of water while being kept in an ice
bath and stirred for 30 min at room temperature. It was then
concentrated until solid started to precipitate out. More water was
added and the solid was collected by filtration. After being washed
with water, the solid was dissolved in methanol/chloroform and
evaporated repeatedly until dry. The crude acid product was
obtained as an orange crystalline solid (100 mg). LC-MS analysis
indicated that this material consisted of approximately 80% of 1:1
mixture of 4 and trifluoroacetylated 4, and can be used satisfactorily
in the subsequent coupling reactions without further purification.
For characterization, this material was treated with saturated sodium
bicarbonate solution and purified by reversed-phase HPLC with a
1
10-50% B gradient. H NMR (500 MHz, DMSO-d6) δ 11.94 (s.
1H), 10.77 (s, 1H), 9.10 (s, 1H), 8.70 (s, 1H), 8.66 (s, 1H), 8.57
(m, 2H), 8.54 (s, 1H), 8.22 (s, 1H), 8.03 (s, 1H) (d, 1H, J ) 9.5
Hz), 7.90 (s, 1H), 7.86 (d, 1H, J ) 11.5 Hz), 7.75 (d, 1H, J ) 8.5
Hz), 7.38 (m, 2H), 7.20 (d, 1H, J ) 7 Hz), 6.38 (d, 1H, J ) 12.0
Hz), 5.76 (dd, 1H, J ) 11.0 and 4.5 Hz), 5.72 (d, 1H, J ) 9.5 Hz),
5.24 (dd, 1H, J ) 11.0 and 4.5 Hz), 5.06 (m, 2H), 5.00 (d, 1H, J
) 8.0 Hz), 4.80 (d, 1H, J ) 10.5 Hz), 4.54 (d, 1H, J ) 11.0 Hz),
4.30 (d, 1H, J ) 9.5 Hz), 4.26 (m, 1H), 4.16 (d, 1H, J ) 10.5 Hz),
4.05 (d, 1H, J ) 8.0 Hz), 3.92 (s, 3H), 3.13 (s, br, 1H), 2.89 (s,
3H), 2.87 (s, 3H), 2.13 (m, 1H), 2.01 (s, 3H), 1.95 (d, 1H, J )
14.5 Hz), 1.61 (s, 3H), 1.57 (s, br, 3H), 0.81 (d, 3H, J ) 6.5 Hz).
(21) Pascard, C.; Ducruix, A.; Lunel, J.; Prange´, T. J. Am. Chem. Soc.
1977, 99, 6418-6423.
(22) Bagley, M. C.; Dale, J. W.; Merritt, E. A.; Xiong, X. Chem. ReV.
2005, 105, 685-714.
(20) The coupling reactions with EDC/HOBt or PyBop converted
nocathiacin acid 4 to amide analogues quantitatively as analyzed by LC-
MS, but isolated yields after reversed-phase HPLC purification typically
fell between 50% and 80%.
(23) Northcote, P. T.; Siegel, M.; Borders, D. B.; Lee, M. D. J. Antibiot.
1994, 47, 901-908.
(24) Bagley, M. C.; Bashford, K. E.; Hesketh, C. L.; Moody, C. J. J.
Am. Chem. Soc. 2000, 122, 3301-3313.
J. Org. Chem, Vol. 72, No. 19, 2007 7449

13C NMR (125 MHz, DMSO-d6) δ 172.1, 168.8, 168.4, 167.6,
164.3, 163.9, 162.3, 161.9, 161.7, 161.2, 160.9, 159.6, 159.9 (q, J
) 96.5 Hz, TFA), 154.9, 152.2, 150.2, 149.4, 147.4, 146.2, 143.9,
135.6, 134.9, 131.1, 130.9, 128.6, 127.6, 127.1, 126.9, 126.4, 126.3,
124.6, 123.8, 120.6, 120.0, 113.4, 111.8, 110.2, 95.3, 79.8, 71.7,
69.7, 68.3, 67.1, 65.8, 65.2, 63.9, 63.5, 56.8, 56.1, 50.6, 50.5, 47.1,
43.0, 38.9, 30.8, 23.2, 18.6, 18.0, 13.7. HRMS-TOF (m/z) [M +
H]+ calcd for C58H56N12O18S5 1369.252, found 1369.258.
(1.55 mL, 16.2 mmol). After 20 min aqueous NH4OH (3.4 mL, 48
mmol) was added to solution, and the mixture was allowed to warm
up to room temperature. The residue was partitioned between water
and ethyl acetate. The organic layer was washed with water and
brine, dried over Na2SO4, and evaporated. Recrystallization from
ethyl acetate/hexanes afforded N-(tert-butoxycarbonyl)-L-(Se)-phe-
1
nylselenocysteine amide as a white solid (4.11 g, 74% yield). H
NMR (500 MHz, CDCl3) δ) 7.60 (dd, J ) 3.6, 7.1 Hz, 2 H), 7.32
(m, 3 H), 6.26 (s, 1 H), 5.48 (s, 1 H), 5.28 (s, 1 H), 4.40 (s, 1 H),
3.35 (s, 1 H), 3.26 (dd, J ) 5.8, 12.2 Hz, 1 H), 1.47 (s, 12 H).
LC-MS (ESI) m/z 344.9 (M + 1).
N-(3-Morpholin-4-yl-propyl)amide 5. Compound 4 (30 mg,
0.016 mmol) was mixed with N-(3-aminopropyl)morpholine (3.5
mg, 0.024 mmol), 1-hydroxybenzotriazole (3.1 mg, 0.020 mmol),
and EDC (5.8 mg, 0.03 mmol) in anhydrous DMF (0.4 mL). After
1 h, the reaction mixture was directly purified by reversed-phase
HPLC with a gradient of 5-45% B. Compound 5 was obtained as
a light yellow solid after lyophilization (TFA salt, 12.5 mg, 49%
The TFA salt of L-(Se)-phenylselenocysteine amide (3 g, 12.3
mmol) obtained after deprotection with 1:1 TFA/CH2Cl2 was
coupled to 2-phenyl-1,3-thiazo-4-carboxylic acid (2.4 g, 11.7 mmol)
in DMF (50 mL) under peptide coupling conditions with EDC (4.49
g, 23.4 mmol) and HOBt (158 mg, 1.17 mmol). After being stirred
at room temperature for 3 h, the mixture was diluted with water
and extracted with ethyl acetate. The organic layer was washed
with water and brine, dried over Na2SO4 and concentrated in vacuo.
Purification by silica gel chromatography (15-80% EtOAc/
hexanes) yielded the N-(2-phenyl-1,3-thiazo-2-lyl)carbonyl-Se-
1
yield). H NMR (500 MHz, CD3OD-d4) δ 8.62 (d, 1H, J ) 9.5
Hz), 8.56 (s, 1H), 8.43 (s, 1H), 8.41 (s, 1H), 8.19 (s, 1H), 8.14 (d,
1H, J ) 11.0 Hz), 7.88 (s, 1H), 7.86 (d, 1H, J ) 7.0 Hz), 7.84 (m,
2H), 7.43 (t, 1H, J ) 8.0 Hz), 7.22 (d, 1H, J ) 7.0 Hz), 6.13 (d,
1H, J ) 13.0 Hz), 5.91 (dd, 1H, J ) 9.5 and 2.0 Hz), 5.78 (dd,
1H, J ) 11.0 and 5.0 Hz), 5.39 (dd, 1H, J ) 11.3 and 5.3 Hz),
5.21 (m, 1H), 5.06 (d, 1H, J ) 12.5 Hz), 4.96 (d, 1H, J ) 10.5
Hz), 4.59 (d, 1H, J ) 11.5 Hz), 4.42 (d, 1H, J ) 10.0 Hz), 4.37
(m, 1H), 4.29 (d, 1H, J ) 10.5 Hz), 4.05-4.18 (m, 4H), 3.96 (s,
3H), 3.80 (m, 2H), 3.53-3.60 (m, 4H), 3.29 (t, 2H, J ) 7.8 Hz),
3.12-3.22 (m, 3H), 3.03 (s, 6H), 2.80 (m, 1H), 2.18 (s, 3H), 2.07
(s, 3H), 1.75 (s, 3H), 1.42 (d, 3H, J ) 6.0 Hz), 1.00 (d, 3H, J )
7.0 Hz). HRMS-TOF (m/z) ([M + 2H]/2)+ calcd for C65H70N14O18S5
748.187, found 748.189.
1
phenylselenocysteine amide (4.64 g, 92% yield). H NMR (500
MHz, DMSO-d6) δ 8.43 (d, J ) 8.3 Hz, 1 H), 8.32 (s, 1 H), 8.03-
8.01 (m, 2 H), 7.66 (s, 1 H), 7.57-7.54 (m, 3 H), 7.50 (t, J ) 4.2
Hz, 2 H), 7.33 (s, 1 H), 7.23-7.15 (m, 3 H), 4.74-4.70 (m, 1 H),
3.47 (dd, J ) 4.9, 12.4 Hz, 1 H), 3.38 (dd, J ) 8.0, 12.5 Hz, 1 H).
LC-MS (ESI) m/z 431.8 (M + 1).
Finally, oxidative elimination was carried out by adding an
aqueous solution of sodium periodate (9.05 g, 42.3 mmol) to a THF
(100 mL) solution of N-(2-phenyl-1,3-thiazo-2-lyl)carbonyl-Se-
phenylselenocysteine amide (4.55 g, 10.6 mmol) at room temper-
ature. After the mixture was stirred for 3 h, precipitate was collected
by filtration and washed with 1:1 THF/water and dried in vacuo to
give N-(2-phenyl-1,3-thiazo-2-lyl)carbonylaminoacrylamide (7) as
4-Methylpiperazin-1-ylamide 6. Compound 4 (30 mg, 0.016
mmol) was mixed with 1-methylpiperazine (2.4 mg, 0.024 mmol),
1-hydroxybenzotriazole (3.1 mg, 0.020 mmol), and EDC (5.8 mg,
0.03 mmol) in anhydrous DMF (0.4 mL) and the mixture was stirred
at room temperature for 1 h. Purification by reversed-phase HPLC
with a gradient of 10-30% B afforded compound 6 as a light
yellow solid after lyophilization (TFA salt, 12 mg, 50% yield). 1H
NMR (500 MHz, CD3OD-d4) δ 8.64 (d, J ) 9.3 Hz, 1 H), 8.59 (s,
1 H), 8.44 (s, 1 H), 8.29 (s, 1 H), 8.20 (s, 1 H), 8.16 (d, J ) 11.0
Hz, 1 H), 7.91-7.83 (m, 4 H), 7.45 (t, J ) 7.7 Hz, 1 H), 7.25 (d,
J ) 7.0 Hz, 1 H), 6.16 (d, J ) 12.5 Hz, 1 H), 5.92 (d, J ) 9.4 Hz,
1 H), 5.79 (dd, J ) 4.8, 10.9 Hz, 1 H), 5.40 (dd, J ) 5.1, 11.4 Hz,
1 H), 5.23 (s, 1 H), 5.08 (d, J ) 12.6 Hz, 1 H), 4.98 (d, J ) 10.5
Hz, 1 H), 4.61 (d, J ) 11.3 Hz, 1 H), 4.43 (d, J ) 9.7 Hz, 1 H),
4.38 (dd, J ) 4.4, 6.7 Hz, 1 H), 4.32 (d, J ) 10.6 Hz, 1 H), 4.16
(q, J ) 7.0 Hz, 1 H), 4.08 (d, J ) 9.6 Hz, 1 H), 3.97 (s, 3 H), 3.35
(m, 2 H), 3.22 (s, 1 H), 3.04 (s, 6 H), 2.96 (s, 3 H), 2.82 (m, 1 H),
2.18 (s, 2 H), 2.07 (s, 3 H), 1.77 (s, 3 H), 1.43 (d, J ) 6.1 Hz, 3
H), 1.01 (d, J ) 7.1 Hz, 3 H). HRMS-TOF (m/z) ([M + 2H]/2)+
calcd for C63H66N14O17S5 726.174, found 726.177.
1
a white solid (3.0 g, 73% yield). H NMR (500 MHz, DMSO-d6)
δ 10.10 (s, 1 H), 8.48 (s, 1 H), 8.15 (s, 1 H), 8.00 (dd, J ) 7.2 Hz,
2 H), 7.66 (s, 1 H), 7.57 (m, 3 H), 6.50 (s, 1 H), 5.77 (s, 1 H). 13
C
NMR (125 MHz, DMSO-d6) δ 168.4, 165.6, 159.3, 134.5, 132.7,
131.7, 127.0, 126.2, 103.0. HRMS-TOF (m/z) [M + H]+ calcd for
C13H11N3O2S 274.065, found 274.067.
Acknowledgment. We thank Dr. Bernard C. Choi for
performing HRMS analyses, and Fermentation Development &
Operations and Biopurification Development for the supply of
nocathiacin I and thiazomycin.
Supporting Information Available: Experimental conditions
for the synthesis and isolation of compounds 8, 11, and 12, copies
of 1H NMR, 13C NMR, and HRMS spectra for compounds 4, 7, 8,
1
and 11, and H NMR and HRMS spectra for compounds 5 and 6.
N-(2-Phenyl-1,3-thiazo-2-lyl)carbonyl aminoacrylamide (7).
To a solution of N-(tert-butoxycarbonyl)-L-(Se)-phenylselenocys-
teine19 (5.6 g, 16.2 mmol) in THF (125 mL) at -15 °C was added
N-methylmorpholine (1.8 mL, 16 mmol) and ethylchloroformate
This material is available free of charge via the Internet at
http://pubs.acs.org.
JO071115P
7450 J. Org. Chem., Vol. 72, No. 19, 2007