Mild method for cleavage of dehydroalanine units: Highly efficient conversion of nocathiacin I to nocathiacin IV

Article abstract of DOI:10.1021/jo0261698

Thiazolyl peptide antibacterial nocathiacin I (1) was converted to nocathiacin IV (4) in high yield using iodomethane and hydriodic acid in THF at 45 °C. Several simplified dehydroalanine-containing systems undergo dehydroalanine cleavage under the same conditions, although in these cases iodomethane is not needed for efficient conversion. The mild reaction conditions are in contrast with other methods described in the literature.

Full text of DOI:10.1021/jo0261698

Mild Meth od for Clea va ge of
Deh yd r oa la n in e Un its: High ly Efficien t
Con ver sion of Noca th ia cin I to Noca th ia cin
IV
Alicia Regueiro-Ren* and Yasutsugu Ueda
The Bristol-Myers Squibb Pharmaceutical
Research Institute, 5 Research Parkway,
Wallingford, Connecticut 06492
alicia.regueiroren@bms.com
Received J uly 9, 2002
Abstr a ct: Thiazolyl peptide antibacterial nocathiacin I (1)
was converted to nocathiacin IV (4) in high yield using
iodomethane and hydriodic acid in THF at 45 °C. Several
simplified dehydroalanine-containing systems undergo de-
hydroalanine cleavage under the same conditions, although
in these cases iodomethane is not needed for efficient
conversion. The mild reaction conditions are in contrast with
other methods described in the literature.
Resistance developed by pathogenic bacteria against
antimicrobial agents has increased worldwide at an
alarming rate, threatening the clinical usefulness of a
number of existing antibacterial agents.1 Reports de-
scribing methicillin-resistant Staphylococcus aureus
(MRSA), vancomycin-resistant Enterococci (VRE), and
penicillin-resistant Streptococcus pneumoniae (PRSP)
highlight the need for alternative antibacterial agents
that retain activity against resistant strains.2
F IGURE 1. Structures of nocathiacins.
out to investigate modifications of this class of compounds
which would maintain the biological activity of noca-
thiacins while increasing their water solubility. One of
our approaches is the introduction of water-solubilizing
groups in amide 4,7 which lacks the dehydroalanine unit
of the side chain present in 1. Although nocathiacin IV
was originally obtained from nocathiacin I enzymati-
cally,8 an alternative and complementary chemical method
which could supply large amounts of 4 more efficiently
would be preferable. In this paper, we described a novel
and highly efficient chemical method for converting
nocathiacin I (1) to nocathiathin IV (4) by selective
cleavage of the dehydroalanine unit.
R,â-Dehydroamino acids, and specifically R,â-dehy-
droalanine, are constituents of a variety of naturally
occurring antibiotic and phytotoxic peptides including the
lantibiotics nisin, subtilin, and epidermin and other
highly modified peptides such as thiostrepton, nosihep-
tide, and berninamycin.9 Several methods have been
reported for the degradation of peptides and other
molecules containing dehydroalanine moieties.10 All of
Nocathiacins3,4 are a new group of thiazolyl peptide
antibiotics isolated from fermentation of Nocardia spp.3
or a fungus Amicolaptosis sp.4 (Figure 1). Nocathiacin I5
(1) has shown high in vitro potency against a variety of
Gram-positive bacteria, including multiple resistant
strains such as MRSA, VRE, and PRSP. More impor-
tantly, nocathiacin I shows in vivo efficacy in a systemic
Staphylococcus aureus infection model in mice.3a In
addition, it appears to be more soluble at low pH than
other thiazolyl peptides such as thiostrepton and nosi-
heptide.6 However, its aqueous solubility is not sufficient
for development as an intravenous agent. As a part of
our efforts to develop new antibacterial agents, we set
(1) For recent reviews on antibacterial resistance, see: (a) Sefton,
A. M. Drugs 2002, 62, 557. (b) Tenover, T. C. Clin. Infect. Dis. 2001,
33 (Suppl. 3), S108. (c) Barbosa, T. M.; Levy, S. B. Drug Resist. Updates
2000, 3, 303.
(2) (a) Bush, K.; Macielag, M.; Clancy, J . Emerging Drugs 2000, 5,
347 and references therein. (b) Walsh, C. Nature 2000, 406, 775 and
references therein.
(3) (a) Leet, J . E.; Ax, H. A.; Gustavson, D. R.; Brown, D. M.; Turner,
L.; Brown, K.; Li, W.; Lam, K. S. US 6,218,398. (b) Li, W.; Leet, J . E.;
Lam, K. S. US 6,287,827. (c) Li, W.; Leet, J . E.; Lam, K. S. PCT Int.
Appl. WO 0014100, 2000.
(4) Sasaki, T.; Otani, T.; Matsumoto, H.; Hamada, M.; Takeuchi,
T.; Hori, M. J . Antibiot. 1998, 51, 715.
(7) Hrnciar, P.; Ueda, Y.; Huang, S.; Leet, J . E.; Bronson, J . J .
Submitted for publication.
(8) (a) Li, W.; Leet, J .; Huang, X.; Lam, K. S.; Regueiro-Ren, A. PCT
Int. Appl. WO0213834, 2002. (b) Li, W.; Leet, J . E.; Ax, H. A.;
Gustavson, D. R.; Brown, D. M.; Turner, L.; Brown, K.; Clark, J .; Yang
H.; Lam, K. S. Manuscript in preparation.
(5) For stereochemical assignment, see: Konstantine, K. L.; Mueller,
L.; Huang, S.; Abid, S.; Lam, K. S.; Li, W.; Leet, J . E. J . Am. Chem.
Soc. 2002, 124, 7284.
(6) The presence of an amino sugar moiety in nocathiacins may
contribute to the improved solubility when compared with other
thiazolyl peptides.
(9) (a) Palmer, D. E.; Pattaroni, C.; Nunami, K.; Chadha, R. K.;
Goodman, M.; Wakamiya, T.; Fukase, K.J . Am. Chem. Soc. 1992, 114,
5634. (b) Suzen, S. Ankara Ecz. Fak. Derg. 1999, 28, 129.
10.1021/jo0261698 CCC: $22.00 © 2002 American Chemical Society
Published on Web 10/30/2002
J . Org. Chem. 2002, 67, 8699-8702
8699

TABLE 1. Con ver sion of Noca th ia cin I (1) to
Noca th ia cin IV (4)a
reaction was observed until H2O was added. Thus, 4 was
formed in 20% yield and an equal amount of an iodo-
hydrin (detected by LC/MS [M + 1]+) 1581)16 was also
produced, although most of the starting material re-
mained unreacted (entry 2). Higher reaction tempera-
tures or addition of more iodine yielded a complex
mixture.
entry
reagent
solvent
DMF
THF/H2O 0-25
DMF
DMF
T (°C) t (h)
4 (%)
1 (%)
b
1
2
3
4
5
6
7
I2
I2
0-25
24
24
3
Hydriodic acid (57% in water) in DMF afforded 20-
40% of 4 and 5-40% of a hydrolysis product resulting
from opening of one of the lactones (detected by LC/MS
[M + 1]+ ) 1455) (entry 3). When iodomethane was used
in combination with HI at 45 °C (entry 4), 4 was obtained
in 60% yield but the reaction could not be driven to
completion without increasing the amount of open lactone
side products. Acetonitrile, MeOH, or dioxane as the
reaction solvent produced similar results. However, the
use of THF as the solvent afforded a dramatic improve-
ment in product yields. Complete conversion to 4 was
achieved (entry 5) while no undesired hydrolysis product
was detected. Also, the transformation occurred smoothly
at a lower reaction temperature and much more rapidly.17
Iodomethane alone in THF was not effective (entry 6).
HI in THF afforded 4 in 40% yield with 50-60% of the
hydrolysis product (entry 7). Several other acids, i.e., HCl,
HBr, and HOAc, were screened using similar experimen-
tal conditions described above and were found to produce
only trace amounts of 4. In most cases, complex mixtures
of many products were detected.
20g
55g
30g
99h
b
HIc
25
45
45
75
25
20-40h
60g
HI/MeId
5
3
HI /MeId THF
86-90h
MeIe
HIf
THF
THF
24
24
40h
a
Reaction conditions: In a sealed tube, 1 mmol of 1 in 4 mL of
THF was treated with the corresponding reagents and heated at
b
the temperature and for the period of time indicated. 6 mmol.
d
c 2-5 mmol. 2 mmol of HI/ 10 mmol of MeI. e 10 mmol. f 2 mmol.
g
h
HPLC ratios. Isolated yields.
them involved relatively harsh conditions such as el-
evated temperatures and strongly acidic, basic, or oxida-
tive reaction media (e.g., aq HCl, 100 °C; H2O, 100 °C;
I2, NaOH; aq Br2; HCHO, H2O2).11 When applied to
nocathiacin I, none of these methods afforded 4 in a
practical manner; instead total destruction of the natural
product occurred. Nocathiacin I (1) contains, among other
features, a tricyclic skeleton attached by two labile
lactone moieties, a vinyl ether, and a dimethylamino
sugar, all of which may not survive under severe reaction
conditions.12 Therefore, it was clear that new reaction
conditions needed to be developed in order to achieve the
desired transformation from 1 to 4 in a useful manner.
We initially observed the conversion of 1 to 413 in 56%
yield upon treating 1 with iodomethane in DMF at 75
°C for 12 h in a sealed tube. However, there were still a
few problems with the reproducibility of these reaction
conditions. Prolonged reaction times and exposure to
open air produced many other degradation products.
Large amounts of iodomethane (40 equiv) were also
needed for completion, and the use of different batches
of reagent led to variable yield.
We contemplated the idea that the active reagent
responsible for the transformation from 1 to 4 may not
be iodomethane but rather some impurities present in
this reagent or other entities generated in the process.
Iodomethane is often an unstable chemical entity and
needs to be stabilized using, for example, copper wire.14
We decided to explore this hypothesis further and treat
1 with iodine or hydriodic acid.15 The results are sum-
marized in Table 1.
The optimal results were obtained when 1 was sus-
pended in THF and treated with 7-10 equiv of MeI and
1.8-3 equiv of HI at 45 °C for 1-5 h.
To study the scope and limitations of this reaction, we
applied the conditions to a few model compounds con-
taining terminal dehydroalanine units, 5-7 (Table 2). In
a typical experiment, 1 mmol of starting material was
dissolved in 4 mL of THF and heated at 45 °C in a sealed
tube with 2 mmol of HI and 10 mmol of MeI for 1 h. In
all cases, the dehydroalanine moiety was cleaved readily
and the desired products were isolated in good yields
(entries 2, 5, and 8). When iodomethane (10 mmol) was
used in the absence of HI, no reaction was observed, even
after 24 h at 75 °C (entries 1, 4, and 7). In contrast, for
these simple substrates hydriodic acid (2 mmol) alone
produced results similar to those when the mixture of
MeI/HI was used (entries 3, 6, and 9). Hydriodic acid in
THF at 45 °C may be an alternative to the use of excess
aqueous HCl solution at 100 °C in thoses cases where
the compounds are insoluble in aqueous solution or
unstable under these conditions.
A terminal tyramine amide was incorporated in one
of the substrates 7 with the purpose of visualizing both
cleaved moieties resulting from the reaction (entries 8
and 9). Along with the expected des-dehydroalanine
amide, tyramine pyruvate 8 was isolated in both cases,
suggesting a hydrolysis mechanism for this reaction
where the MeI may not be involved (Scheme 1). In the
presence of acid, the enamide can equilibrate to the
iminium form, which is then attacked by water to produce
Iodine in DMF produced only decomposition of the
starting material (entry 1) while with iodine in THF no
(10) (a) Bergman, M.; Grafe, K. Z. Physiol. Chem. 1930, 187. (b)
Patchornik, A.; Sokolowsky, M. J . Am. Chem. Soc. 1964, 86, 1206.
(11) The peptides where these conditions were successfully used
were simple synthetic dipeptides (see ref 10). To the best of our
knowledge, there is no report about their use in natural or structurally
more complex peptides.
(12) Oxidation of the dimethylamino sugar, cleavage of the sugar
moiety, and lactone opening are among the side reactions observed.
(13) The synthetic product was found to be identical to a sample of
nocathiacin IV obtained by enzymatic cleavage of 1.
(16) Iodohydrin can be formed by H2O attack to an iodonium
intermediate from reaction between iodine and the olefin of the
dehydroalanine moiety.
(17) Reaction time was reduced from >12 h to 1 h in small scale
(<1.0 g) and 3-5 h for larger scale (1-10 g).
(14) Sulikowski, G. A.; Sulikowski, M. M. In Encyclopedia of the
Reagents; Paquette, L. A., Ed.; J ohn Wiley & Sons: New York, 1995;
Vol. 4, p 2828.
(15) HI may be present by reaction of MeI with H2O.
8700 J . Org. Chem., Vol. 67, No. 24, 2002

TABLE 2. Deh yd r oa la n in e Clea va ge of Sim p lified System sa
a
Reaction conditions: In a sealed tube, 1 mmol of compound in 4 mL of THF was treated with the corresponding reagents and heated
at the temperature and for the period of time indicated. 10 mmol. c 10 mmol of MeI/2 mmol of HI. 2 mmol. e Isolated yields.
b
d
iodomethane (1.0 mL, 16 mmol). The reaction mixture was
heated in a sealed tube at 45 °C for 5 h before it was allowed to
cool to room temperature. Diethyl ether (25 mL) was added, and
the resulting yellow precipitate was collected by filtration,
washed with diethyl ether (3 × 25 mL), and dried under reduced
pressure to afford the HI salt of nocathiacin IV (4) (3.4 g, 88%
yield) as a bright yellow solid. For characterization, this material
was further purified as the TFA salt using reversed-phase
chromatography (preparative C-18 column using CH3CN/H2O/
1%TFA as mobile phase, gradient elution 10-50%). Analytical
data for 4: yellow solid; 1H NMR (500 MHz, DMSO-d6) δ 10.84
(1 H, s), 10.78 (1 H, s), 9.11 (1 H, s), 8.65 (1 H, s), 8.59 (1 H, br),
8.57 (1 H, br), 8.54 (1 H, s), 8.46 (1 H, s), 8.22 (1 H, s), 7.99 (1
H, s), 7.89 (1 H, s), 7.86 (1 H, d, J ) 11.0 Hz), 7.75 (1 H, d, J )
8.5 Hz), 7.71 (1 H, s), 7.37 (2 H, m), 7.19 (1 H, d, J ) 7.0 Hz),
6.02 (1 H, d, J ) 12.0 Hz), 5.76 (1 H, dd, J ) 11.2, 4.2 Hz), 5.72
(1 H, d, J ) 10.0 Hz), 5.23 (1 H, m), 5.05 (3 H, m), 4.79 (1 H, d,
J ) 10.5 Hz), 4.53 (1 H, d, J ) 11.0 Hz), 4.30 (1 H, d, J ) 9.5
Hz), 4.25 (1 H, m), 4.16 (3 H, d, J ) 0.5 Hz), 4.05 (1 H, dd, J )
9.5, 1.5 Hz), 3.91 (1 H, s), 3.87 (1 H, s), 3.13 (1 H, br), 2.88 (6 H,
m), 2.50 (1 H, br), 2.12 (1 H, m), 2.0 (3 H, s), 1.94 (1 H, d, J )
14.5 Hz), 1.60 (3 H, s), 1.52 (1 H, d, J ) 7.0 Hz), 1.17 (3 H, br),
0.8 (3 H, d, J ) 7.0 Hz); 13C NMR (125.8 MHz, DMSO-d6) δ 171.3,
168.0, 167.8, 167.6, 166.8, 163.6, 163.1, 161.4, 160.9, 160.4, 160.2,
158.7, 154.1, 150.9, 150.6, 149.5, 148.6, 145.39, 143.1, 134.8,
134.2, 130.1, 127.8, 127.4, 126.7, 126.3, 126.1, 125.6, 125.5, 123.8,
123.0, 119.8, 119.3, 112.7, 111.0, 109.4, 94.5, 78.9, 72.2, 70.9,
68.8, 67.5, 66.3, 65.1, 64.4, 63.0, 62.7, 56.0, 49.9, 49.7, 46.5, 42.1,
38.1, 30.0, 17.7, 17.3, 12.9; HR-ESI MS [M + H]+ m/z calcd for
SCHEME 1. P r op osed Mech a n ism for
Deh yd r oa la n in e Clea va ge
the corresponding truncated amide and tyramine pyru-
vate 8.
In summary, a practical and efficient conversion of
antibacterial nocathiacin I (1) to nocathiacin IV (4) has
been developed. Cleavage of the dehydroalanine unit
present in 1 is achieved by using a mixture of iodo-
methane and hydriodic acid in THF at 45 °C. The
conditions are useful also for the cleavage of dehydroala-
nine units in simple substrates although in these cases
iodomethane is not required. This mild method represent
a convenient alternative to other processes published in
the literature which usually employ harsh conditions
which are incompatible with other labile functional
groups.
C
58H57N13O17S5 1368.267, found 1368.267; ESI-MS/MS fragmen-
tation ions m/z 1197, 1179, 1153, 1135, 1117, 719; major IR
bands (cm-1) 3438, 1676, 1536, 1475, 1204, 1132, 596; UV λmax
(MeOH) nm 219, 294, 359; CD λ nm (∆ꢀ) (MeOH) 305.2 (-5.7),
265.2 (+15.8), 236.6 (-44.1), 209.6 (+29.6).
P r ep a r a t ion of N-(1-Ca r b a m oylvin yl)b en za m id e (5).
Compound 5 was prepared in three steps from commercially
available DL-serine methyl ester and benzoyl chloride as fol-
lows: Benzoyl chloride (5.38 mL, 46.6 mmol) was added dropwise
to a stirred solution of serine methyl ester hydrochloride (7.26
g, 46.6 mmol) and triethylamine (16.0 mL, 116 mmol) in
anhydrous CH2Cl2 (100 mL), and the mixture was stirred at rt
for 4 h. A saturated aqueous solution of NaHCO3 was added,
and the organic phase was extracted with CH2Cl2. The combined
organic layers were dried over NaSO4, filtered, and concentrated.
The crude residue was taken to the next step without further
Exp er im en ta l Section
Gen er a l Meth od s. Solvents and other reagents were used
as purchased without further purification. Reactions were
monitored by LC/MS. Detection (UV) was at 220 nm. Compounds
were purified by reversed-phase HPLC chromatography using
MeOH/H2O/0.1%TFA (gradient elution 30-100%) as mobile
phase, unless otherwise specified.
P r ep a r a tion of Noca th ia cin IV (4). A suspension of no-
cathiacin I (1) (3.1 g, 2.1 mmol) in THF (10 mL) was treated
with hydriodic acid (57% in water, 0.8 mL, 3.8 mmol) and
J . Org. Chem, Vol. 67, No. 24, 2002 8701

purification. Mesylation of the alcohol followed by elimination
was accomplished in one pot by treatment of the crude from
above with triethylamine (16.0 mL, 46.6 mmol) and mesyl
chloride (5.4 mL, 70.0 mmol) in CH2Cl2 (100 mL) at rt overnight.
Methanol (5 mL) was added, and the stirring was continued for
15 min. Water was added, and the organic phase was extracted
with CH2Cl2, dried over NaSO4, filtered, concentrated, and
chromatographed in silica gel using 20%AcOEt/hexanes to afford
2-benzoylaminoacrylic acid methyl ester (7.73 g, 81% in two
steps): white solid; mp 205 °C; 1H NMR (300 MHz, CDCl3) δ
8.57 (1 H, bs), 7.85 (2 H, m), 7.49 (3 H, m), 6.80 (1 H, s), 5.59 (1
H, s), 3.91 (3 H, s); MS (ESI) (M + H)+ 206.1, (M - H)- 204.1.
The 2-benzoylaminoacrylic acid methyl ester was treated with
a 6 N solution of ammonia in MeOH (25 mL) at rt for 6 h. After
the solvent was removed in vacuo, the residue was purified to
afford compound 5 (3.22, 45%): white solid; mp 85-87 °C;1H
NMR (300 MHz, CDCl3) δ 8.92 (1 H, bs), 7.84 (2 H, m), 7.47 (3
H, m), 6.75 (1 H, s), 5.38 (1 H, s); 13C NMR (125.8 MHz, CDCl3)
δ 166.0, 134.4, 133.5, 132.2, 128.9, 127.1, 102.7; MS (ESI) (M +
H)+ 191.4, (M - H)- 189.2.
P r ep a r a t ion of 2-(2-P h en oxyp r op ion yla m in o)a cr yla -
m id e (6). Compound 6 was prepared in three steps from
commercially available 2-phenoxypropionyl chloride and DL-
serine methyl ester as follows: 2-Phenoxypropionyl chloride
(16.7 mL, 0.1 mol) was added dropwise to a stirred solution of
serine methyl ester hydrochloride (16.6 g, 0.1 mol) and trieth-
ylamine (46 mL, 0.3 mol) in anhydrous CH2Cl2 (250 mL), and
the mixture was stirred at rt for 2 h. A saturated aqueous
solution of NaHCO3 was added, and the organic phase was
extracted with CH2Cl2. The combined organic layers were dried
over NaSO4, filtered, and concentrated. The crude residue was
dissolved in CH2Cl2 (250 mL) and treated with triethylamine
(46 mL, 0.3 mol) and mesyl chloride (12.5 mL, 0.16 mol), and
the reaction mixture was stirred at rt overnight. Methanol (25
mL) was added, and the stirring was continued for 15 min. Water
was added, and the organic phase was extracted with CH2Cl2,
dried over NaSO4, filtered, concentrated, and chromatographed
in silica gel using AcOEt/hexanes (gradient elution: 0-30%) to
afford 2-(2-phenoxypropionylamino)acrylic acid methyl ester
(18.9 g, 76%): white solid; mp 272-273 °C; 1H NMR (500 MHz,
CDCl3) δ 8.85 (1 H, bs), 7.29 (2 H, m), 7.02 (1 H, m), 6.96 (2 H,
m), 6.66 (1 H, s), 5.92 (1 H, s), 4.74 (1 H, q, J ) 7 Hz), 3.82 (3 H,
s), 1.61 (3 H, d, J ) 7 Hz); 13C NMR (125.8 MHz, CDCl3) δ 171.1,
164.2, 156.8, 130.7, 129.9, 122.4, 115.8, 109.4, 75.3, 53.0, 18.6;
GC (MS) 249.
1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride
(EDC) (9.9 g, 52 mmol) and stirred at rt for 12 h. Water was
added, and the organic phase was extracted with AcOEt and
CHCl3. The combined organic phase was dried over Na2SO4,
filtered, and concentrated. The residue was purified to afford
compound 6 (3.1 g, 50%): white solid; mp 165-167 °C; 1H NMR
(300 MHz, CDCl3) δ 9.13 (1 H, bs), 7.27 (2 H, m), 6.93 (3 H, m),
6.57 (1 H, s), 5.33 (1 H, s), 4.73 (2 H, d, J ) 7.0 Hz), 1.60 (3 H,
d, J ) 7.0 Hz); 13C NMR (125.8 MHz, CDCl3) δ 171.4, 165.6,
156.9, 133.2, 129.9, 122.4, 115.9, 103.4, 75.4, 18.7; MS (ESI)
(M + 1)- 233.
P r ep a r a t ion
of N-[2-(4-H yd r oxyp h en yl)et h yl]-2-(2-
p h en oxyp r op ion yla m in o)a cr yla m id e (7). A mixture of 2-(2-
phenoxypropionylamino)acrylic acid (6.1 g, 26 mmol) from above
and tyramine (7.1 g, 52 mmol) in THF (250 mL) was treated
with 4-methylmorpholine (17 mL, 154 mmol), HOBt (7.1 g, 52
mmol), and EDC (9.9 g, 52 mmol) and stirred at rt for 1 h. Water
was added, and the organic phase was extracted with AcOEt
and CHCl3. The combined organic phase was dried over Na2-
SO4, filtered, and concentrated. The residue was purified to
afford compound 7 (3.12 g, 34%): white solid; mp 53-55 °C; 1H
NMR (300 MHz, CDCl3) δ 9.18 (1 H, bs), 7.27 (2 H, m), 6.96 (6
H, m), 6.78 (2 H, m), 6.43 (1 H, d, J ) 1.8 Hz), 6.24 (1 H, bs),
5.12 (1 H, s), 4.73 (1 H, q, J ) 6.8 Hz), 3.50 (2 H, m), 2.75 (2 H,
m), 1.60 (3 H, d, J ) 6.8 Hz); 13C NMR (125.8 MHz, CDCl3) δ
171.6, 163.7, 156.8, 154.9, 134.0, 130.1, 129.9, 122.3, 116.1, 115.8,
115.5, 102.0, 75.2, 41.5, 34.5, 18.6; MS (ESI) (M + H)+ 355.4,
(M - H)- 353.2; HR-ESI MS [M - H]- m/z calcd for C20H21N2O4
353.150, found 353.149.
Hyd r olysis of Com p ou n d 7. To a solution of 7 (354 mg, 1.0
mmol) in THF (3 mL) in a sealed tube was added hydriodic acid
(57% in H2O, 0.45 mL, 2.0 mmol), and the mixture was heated
at 45 °C for 1 h. The volatiles were removed in vacuo, and the
residue was purified to afford tyramine pyruvate (N-[2-(4-
hydroxyphenyl)ethyl]-2-oxopropionamide) 8 (80 mg, 79%) [white
1
solid; mp 71-73 °C; H NMR (300 MHz, CDCl3) 7.02 (2 H, d, J
) 8.4 Hz), 6.77 (2 H, d, J ) 8.4 Hz), 3.50 (2 H, q, J ) 7.0 Hz),
2.76 (2 H, d, J ) 7.0 Hz), 2.45 (3 H, s); 13C NMR (75.5 MHz,
CDCl3) δ 197.0, 160.3, 154.8, 129.8, 115.7, 40.9, 34.5, 24.5; MS
(ESI) (M - H)- 206.2] and 2-phenoxypropionamide (68 mg,
83%): white solid; mp 118-120 °C; 1H NMR (300 MHz, CDCl3)
7.29 (2 H, m), 7.01 (1 H, m), 6.91 (2 H, m), 6.42 (1 H, bs), 6.15
(1 H, bs), 4.65 (2 H, q, J ) 6.5 Hz), 1.58 (3 H, d, J ) 6.5 Hz); 13
C
NMR (75.5 MHz, CDCl3) δ 175.4, 157.0, 129.9, 122.2, 115.5, 74.8,
18.7; MS (ESI) (M - H)- 164.
2-(2-Phenoxypropionylamino)acrylic acid methyl ester (18.9
g, 75.9 mmol) was dissolved in a mixture of THF (100 mL) and
water (10 mL) and treated with lithium hydroxide (15.5 g, 0.37
mol). The reaction was heated at 40 °C for 15 min, and then a
solution of 1 N HCl was added until pH ) 1. EtOAc was used to
extract the organic phase. The combined organic phase was dried
over Na2SO4, filtered, and concentrated. The crude was purified
to afford 2-(2-phenoxypropionylamino)acrylic acid (18.2 g, 99
%): white solid; mp 135-137 °C;1H NMR (500 MHz, CDCl3) δ
8.82 (1 H, bs), 7.30 (2 H, m), 7.02 (1 H, m), 6.96 (2 H, m), 6.75
(1 H, s), 6.08 (1 H, d, J ) 1 Hz), 4.77 (1 H, q, J ) 7 Hz), 1.61 (3
H, d, J ) 7 Hz); 13C NMR (125.8 MHz, CDCl3) δ 171.5, 167.7,
156.7, 130.1, 129.9, 122.5, 115.9, 111.9, 75.2, 18.6; MS (ESI) (M
- 1)- 334.2.
Ack n ow led gm en t. We thank Dr. Narasimhulu
Naidu for useful discussions and the generous supply
of an authentic sample of 2-phenoxypropionamide, the
Natural Product group in Wallingford for the supply of
an authentic sample of nocathiacin IV, and the Process
Research group in New Brunswick for the bulk supply
of nocathiacin I.
Su p p or tin g In for m a tion Ava ila ble: Copies of 1H NMR,
13C NMR, and MS spectra for compounds 4-8 as well as for
2-phenoxypropionamide and intermediates involved in the
syntheses of 5-7. This material is available free of charge via
the Internet at http://pubs.acs.org.
A mixture of 2-(2-phenoxypropionylamino)acrylic acid (6.1 g,
26 mmol) and ammonium chloride (2.78 g, 52 mmol) in THF
(250 mL) was treated with 4-methylmorpholine (17 mL, 154
mmol), 1-hydroxybenzotriazole (HOBt) (7.1 g, 52 mmol), and
J O0261698
8702 J . Org. Chem., Vol. 67, No. 24, 2002