Stereochemical Definition and Chirospecific Synthesis of the Peptide Deformylase Inhibitor Sch 382583

Article abstract of DOI:10.1021/jo035667t

The recently reported natural product Sch 382583 (1), an inhibitor of peptide deformylase, has been synthesized in 16 steps from commercially available starting materials. The three chiral centers were set by a combination of chiral auxiliary and chiral p

Full text of DOI:10.1021/jo035667t

Ster eoch em ica l Defin ition a n d
Ch ir osp ecific Syn th esis of th e P ep tid e
Defor m yla se In h ibitor Sch 382583
Reed A. Coats, Sheng-Lian Lee, Kari A. Davis,
Kanu M. Patel, Elaine K. Rhoads, and
Michael H. Howard*
Stine-Haskell Research Center, DuPont Crop Protection,
1090 Elkton Road, Newark, Delaware 19711
FIGURE 1. Natural product inhibitors of peptide deformylase.
michael.h.howard-1@usa.dupont.com
Received November 12, 2003
promising antimicrobial target.4 Small-molecule inhibi-
tors of this enzyme, representing over a dozen distinct
chemical classes, have been discovered by means of (1)
high-throughput screening of diverse compounds from
private chemical databases, (2) screening of libraries of
known metalloprotease inhibitors, and (3) design based
on substrate or proposed transition-state structure.5 Most
of these inhibitors share with actinonin a hydroxamic
acid moiety that binds to the active site iron cofactor of
PDF, which is essential for enzymatic activity. However,
the synthetic inhibitors, while potent against the isolated
enzyme, have largely proven disappointing in terms of
antibacterial activity when compared to actinonin and
related analogues.5f,6
Abstr a ct: The recently reported natural product Sch
382583 (1), an inhibitor of peptide deformylase, has been
synthesized in 16 steps from commercially available starting
materials. The three chiral centers were set by a combination
of chiral auxiliary and chiral pool approaches. The succinate
5 and piperazic acid 9 moieties were obtained by Evans
oxazolidinone imide enolate alkylation and hydrazination/
cyclization, respectively, and the aminohexanone side chain
13 was prepared via Grignard substitution of the Weinreb
amide derived from L-valine. Spectroscopic data for the
resulting synthetic material, compared with the data re-
ported for the natural product, established that the previ-
ously unassigned valine ketone stereocenter (C-4) has the
S-configuration.
Recognizing the value of natural products as potent,
bioavailable PDF inhibitors, we became quite interested
in a recent report from the Schering-Plough group
describing the isolation and structure determination of
Sch 382583 (1) from Streptomyces.7 With a Ki of 60 nM,
this piperazic acid-containing pseudopeptide is the most
potent carboxylic acid inhibitor of PDF reported to date.
While structurally similar to the matlystatins8 as well
as actinonin, Sch 382583 contains a unique succinamide
side chain substituted by a 3-methylbutyl group. There
are several features of this new natural product that
make it an important target for synthesis. We viewed
the conformational rigidity imparted by the piperazic acid
ring as useful for evaluating the effect of ligand structure
on enzyme activity. Also, unlike the hydroxamic acid-
containing actinonin, Sch 382583 is a carboxylic acid.
Because carboxylic acid inhibitors of a closely related
class of enzymes, the matrix metalloproteases, are con-
siderably less potent than the corresponding hydroxamic
acids,9 it seemed likely that the activity of Sch 382583
could be enhanced via modification of the metal-binding
group.10 Finally, on the basis of the X-ray structure of a
Natural products, particularly those derived from
microbial fermentation, have served as a rich source of
drugs and agrochemicals, as well as lead structures in
the search for bioactive molecules in general.1 The
naturally occurring antibacterial actinonin (Figure 1) has
been identified as a potent inhibitor2 of peptide defor-
mylase (PDF), a hydrolase enzyme that catalyzes the
cleavage of the formyl group at the N-terminal methio-
nine residue of nascent polypeptides in bacterial protein
translation.3 As this process is not part of mammalian
protein biosynthesis, PDF has been identified as a
* To whom correspondence should be addressed. Tel: (302) 451-4796.
(1) (a) Newman, D. J .; Cragg, G. M.; Snader, K. M. Nat. Prod. Rep.
2000, 17, 215-234. (b) Demain, A. L. Spec. Publ. R. Soc. Chem. 2000,
257, 3-16.
(2) Chen, D. Z.; Patel, D. V.; Hackbarth, C. J .; Wang, W.; Dreyer,
G.; Young, D. C.; Margolis, P. S.; Wu, C.; Ni, Z.-J .; Trias, J .; White, R.
J .; Yuan, Z. Biochemistry 2000, 39, 1256-1262.
(3) Vaughan, M. D.; Sampson, P. B.; Honek, J . F. Curr. Med. Chem.
2002, 9, 385-409.
(4) Giglione, C.; Pierre, M.; Meinnel, T. Mol. Microbiol. 2000, 36,
1197-1205.
(5) (a) For an excellent review of the peptide deformylase inhibitor
literature, see: Clements, J . M.; Ayscough, A. P.; Keavey, K.; East, S.
P. Curr. Med. Chem. Anti Infect. Agents 2002, 1, 239-249. Subsequent
reports of inhibitors: (b) Takayama, W.; Shirasaki, Y.; Sakai, Y.;
Nakajima, E.; Fujita, S.; Sakamoto-Mizutani, K.; Inoue, J . Bioorg. Med.
Chem. Lett. 2003, 13, 3273-3276. (c) Hu, X.; Nguyen, K. T.; Verlinde,
C. L. M. J .; Hol, W. G. J .; Pei, D. J . Med. Chem. 2003, 46, 3771-3774.
(d) Smith, K. J .; Petit, C. M.; Aubart, K.; Smyth, M.; McManus, E.;
J ones, J .; Fosberry, A.; Lewis, C.; Lonetto, M.; Christensen, S. B.
Protein Sci. 2003, 12, 349-360. (e) Harris, M. S.; Bock, J . H.; Choi,
G.; Cialdella, J . S.; Curry, K. A.; Deibel, M. R., J r.; J acobsen, E. J .;
Marshall, V. P.; Murray, R. W., J r.; Vosters, A. F.; Wolfe, C. L.; Yem,
A. W.; Baldwin, E. T. Acta Crystallogr., Sect. D 2002, D58, 2153-2156.
(f) Hackbarth, C. J .; Chen, D. Z.; Lewis, J . G.; Clark, K.; Mangold, J .
B.; Cramer, J . A.; Margolis, P. S.; Wang, W.; Koehn, J .; Wu, C.; Lopez,
S.; Withers, G., III; Gu, H.; Dunn, E.; Kulathila, R.; Pan, S.-H.; Porter,
W. L.; J acobs, J .; Trias, J .; Patel, D. V.; Weidmann, B.; White, R. J .;
Yuan, Z. Antimicrob. Agents Chemother. 2002, 46, 2752-2764.
(6) Clements, J . M.; Beckett, R. P.; Brown, A.; Catlin, G.; Lobell,
M.; Palan, S.; Thomas, W.; Whittaker, M.; Wood, S.; Salama, S.; Baker,
P. J .; Rodgers, H. F.; Barynin, V.; Rice, D. W.; Hunter, M. G.
Antimicrob. Agents Chemother. 2001, 45, 563-570.
(7) (a) Chu, M.; Mierzwa, R.; He, L.; Xu, L.; Gentile, F.; Terracciano,
J .; Patel, M.; Miesel, L.; Bohanon, S.; Kravec, C.; Cramer, C.; Fischman,
T. O.; Hruza, A.; Ramanathan, L.; Shipkova, P.; Chan, T. M. Tetra-
hedron Lett. 2001, 42, 3549-3551. (b) Madison, V.; Duca, J .; Bennett,
F.; Bohanon, S.; Cooper, A.; Chu, M.; Desai, J .; Girijavallabhan, V.;
Hare, R.; Hruza, A.; Hendrata, S.; Huang, Y.; Kravec, C.; Malcolm,
B.; McCormick, J .; Miesel, L.; Ramanathan, L.; Reichert, P.; Saksena,
A.; Wang, J .; Weber, P. C.; Zhu, H.; Fischmann, T. Biophys. Chem.
2002, 101-102, 239-247.
(8) Haruyama, H.; Ohkuma, Y.; Nagaki, H.; Ogita, T.; Tamaki, K.;
Kinoshita, T. J . Antibiot. 1994, 47, 1473-1480.
(9) Skiles, J . W.; Gonnella, N. C.; J eng, A. Y. Curr. Med. Chem. 2001,
8, 425-474.
10.1021/jo035667t CCC: $27.50 © 2004 American Chemical Society
Published on Web 01/31/2004
1734
J . Org. Chem. 2004, 69, 1734-1737

SCHEME 2. Syn th esis of (3S)-N-Cbz-p ip er a zic
Acid (9)a
F IGURE 2. Retrosynthetic analysis of 1.
SCHEME 1. Syn th esis of th e Ch ir a l Su ccin a te 5a
a
Reagents: (a) n-BuLi, THF, (S)-(-)-4-benzyl-2-oxazolidinone,
-78 °C, 85%; (b) LDA, di-tert-butyl azodicarboxylate, DMPU, -78
°C, 99%; (c) LiOH, 0 °C, 76%; (d) CF3CO2H, 66%; (a)-(d) see ref
14; (e) 1 N aq NaOH, PhCH3, ClCO2Bn, 40%, see ref 15; (f) HCl/
dioxane, rt; (g) (iPr)2NEt, ClCO2Bn, 0 °C, 69% (from 6); (h) LiOH,
0 °C, 67%.
a
Reagents: (a) SOCl2, 80%; (b) (S)-(-)-4-benzyloxazolidinone,
n-BuLi, THF, -78 °C, 49%; (c) NaN(Si(CH3)3)2, tert-butyl bro-
moacetate, THF, -78 °C, 42%; (d) LiOH, H2O2, 99%.
SCHEME 3.
Syn th esis of (S)-4-Am in o-5-m eth yl-3-
h exa n on e Hyd r och lor id e (14)a
close analogue cocrystallized with PDF,7 the stereochem-
istries of the asymmetric centers at C-7 and C-14 in Sch
382583 were inferred to be S and R, respectively. Because
of the low resolution in that region of the inhibitor-
enzyme complex, the stereochemistry at the final center,
C-4, could not be established and remained unassigned
until the present study.
The first total synthesis of 1 is reported herein, with
assignment of absolute stereochemistry at all three chiral
centers. Our synthetic approach involved a convergent
synthesis utilizing the three major disconnects shown in
Figure 2.
The required chiral succinic acid was prepared using
the Evans oxazolidinone alkylation method as shown in
Scheme 1.11 Treatment of commercially available 5-meth-
ylhexanoic acid with thionyl chloride gave the acid
chloride 2,12 which was reacted with the chiral auxiliary
(S)-(-)-4-benzyloxazolidinone and n-BuLi in THF at -78
°C to yield the intermediate imide 3. The imide was
alkylated stereospecifically with tert-butyl bromoacetate
by generation of the enolate anion with sodium hexa-
methyldisilazide to give 4.
a
Reagents: (a) EtMgBr, THF, 0 °C, 94%; (b) HCl, dioxane, rt,
83%.
dard conditions. The optical purity of the product 5 was
determined by conversion to diastereomeric amides with
(R)- and (S)-phenylalanine methyl ester, respectively.
HPLC co-injection of aliquots of the diastereomeric amide
mixture formed from the (S)-amino ester with the amide
mixture from the (R)-amino ester established the optical
purity of the succinate 5 as >98% ee.
Piperazic acid is a hydrazino amino acid found in many
biologically active natural products.13 To form the amide
bond at N-2, we first needed to protect the more nucleo-
philic nitrogen (N-1) of piperazic acid. The carbobenzoxy
(Cbz) protecting group was chosen because we anticipated
its facile cleavage by hydrogenolysis as being an attrac-
tive option for the final step in the synthesis of Sch
382583. Preparation of the Cbz-protected piperazic acid
(9) has been reported in both racemic and chiral forms.
For our needs, we found that the chiral enolate hydrazi-
nation/cyclization route of Hale and co-workers, as shown
in Scheme 2, provided sufficient quantities of the triflu-
oroacetate salt of the (3S)-piperazic acid (8).14 In our
hands, variable results were obtained when this salt was
Cleavage of the chiral auxiliary of 4 to yield the
monoprotected succinate 5 was performed under stan-
(10) After the completion of our Sch 382583 synthesis, a report from
the British Biotech group on modification of the metal-binding group
of a synthetic PDF inhibitor, BB-3497, appeared: Smith, H. K.;
Beckett, R. P.; Clements, J . M.; Doel, S.; East, S. P.; Launchbury, S.
B.; Pratt, L. M.; Spavold, Z. M.; Thomas, W.; Todd, R. S.; Whittaker,
M. Bioorg. Med. Chem. Lett. 2002, 12, 3595-3599.
(11) Evans, D. A.; Wu, L. D.; Wiener, J . J . M.; J ohnson, J . S.; Ripin,
D. H. B.; Tedrow, J . S. J . Org. Chem. 1999, 64, 6411-6417.
(12) Goerner, G. L.; Muller, H. L.; Corbin, J . L. J . Org. Chem. 1959,
24, 1561-1563.
(13) Ciufolini, M. A.; Xi, N. Chem. Soc. Rev. 1998, 27, 437-445.
J . Org. Chem, Vol. 69, No. 5, 2004 1735

SCHEME 4. Assem bly of 1a
a
Reagents: (a) cyanuric fluoride, CH2Cl2, 5 °C, 91%; (b) (iPr)2NEt, 9, rt to 45 °C, 34%; (c) (EtO)2P(O)CN, 14, 0 °C, 45%; (d) CF3CO2H,
CH2Cl2, 80%; (e) 10% Pd-C, MeOH, rt, 94%.
converted to the protected form of the acid. Conditions
set forth by Adams and co-workers15 for conversion of the
racemic piperazic acid were utilized in converting the
chiral salt 8 to 9 in 40% yield. The low yield of this
unoptimized reaction may be due to the water solubility
of the product, possible side reaction at N-2, or other
undetermined causes.
More conveniently, compound 9 can be obtained as
shown in Scheme 2. The biscarbamate 6 was treated with
HCl in dioxane to yield compound 10. Treatment of com-
pound 10 with Hunig’s base and benzyl chloroformate
resulted in compound 11 in 69% yield. Subsequent hy-
drolysis of the chiral oxazolidin-2-one of 11 afforded the
desired 9 with an overall yield of 46% from compound 6.
The third portion of the molecule was prepared as
shown in Scheme 3 by reacting the Weinreb amide of Boc-
L-valine (12) with ethylmagnesium bromide in THF to
give the protected amino ketone 13. Deprotection of 13
with anhydrous HCl gave the desired amino ketone 14 as
the hydrochloride salt. The general knowledge that amino
ketones are relatively unstable16 prompted us to prepare
14 as needed from 13. Synthesis of the amino ketone 14
has been reported previously via N-methyl-O-methyl-N-
Cbz-valine.17 However, we have found the commercially
available Weinreb amide 12 to be equally serviceable.
The assembly of our three chiral building blocks is
shown in Scheme 4. To avoid an additional protection/
deprotection sequence, we decided to couple the free
piperazic acid 9 to the succinate 5.18 Using the methodol-
ogy developed by Carpino,19 reaction of 5 with cyanuric
fluoride gave the intermediate acid fluoride 15, which
was reacted with acid 9 to give succinamide 16. This
compound was treated with an excess of amino ketone
14 under basic conditions in the presence of diethyl
phosphorylcyanidate17 to give amide 17.
Treatment of the tert-butyl ester 17 with trifluoroacetic
acid yielded acid 18, and catalytic hydrogenation to
remove the benzyl carbamate of 18 provided 1 as a thick
oil. The 1H NMR and 13C NMR spectra data of the
synthetic material prepared in this study were identical
to the data reported for the natural product by Chu and
co-workers.7
In conclusion, this 16-step synthesis of 1, a structurally
unique inhibitor of the important antibacterial target
peptide deformylase, establishes the absolute stereo-
chemistry as S for the amino ketone side chain (C-4).
Efficiency in the number of steps was achieved by direct
coupling of the unprotected piperazic acid 9 to the
succinate 5. This convergent synthesis has proven ame-
nable to the preparation of analogues that are useful for
the establishment of structure-activity trends. Those
results will be reported in due course.
Exp er im en ta l Section
Gen er a l P r oced u r es. Melting points were obtained in open
capillaries and are reported uncorrected. Reactions were carried
out under an atmosphere of dry nitrogen. Organic extracts were
dried with MgSO4 before concentration at reduced pressure
using a rotary evaporator. Specific rotations [R]D were calculated
from the observed rotations as a solution in methanol unless
noted. All IR spectra were recorded as Nujol mulls unless noted.
1H and 13C NMR spectra were obtained on a 300 MHz instru-
ment and are reported in parts per million in deuteriochloroform
relative to tetramethylsilane (0.0 ppm) unless noted. An internal
1
standard of CFCl3 was used for 19F spectra. Significant H NMR
data are tabulated in the order multiplicity (s, singlet; d, doublet;
t, triplet; q, quartet; br, broad), number of protons, and coupling
constant(s) in hertz (Hz).
(S)-1-(1-Meth yleth yl)-2-oxobu tyl)ca r ba m ic Acid 1,1-Di-
m eth yleth yl Ester (13). A 3.0 M solution of ethylmagnesium
bromide in diethyl ether (25 mL, 75 mmol) was added at 0 °C to
the Weinreb amide 12 (4.0 g, 15.4 mmol) in 35 mL of THF over
20 min, maintaining the internal temperature below 5 °C. The
mixture was stirred for 4 h and then quenched by slow addition
of 1 M HCl (10 mL) and diethyl ether (30 mL). The mixture was
extracted into ether and washed with water and then brine,
dried, filtered, and concentrated. The resulting oil was purified
by column chromatography (10-30% EtOAc in hexanes to isolate
the BOC-protected amino ketone 13 as a solid (3.0 g, 91%): mp
(14) Hale, K. J .; Cai, J .; Delisser, V.; Manaviazar, S.; Peak, S. A.;
Bhatia, G. S.; Collins, T. C.; J ogiya, N. Tetrahedron 1996, 52, 1047-
1068.
(15) Adams, C. E.; Aguilar, D.; Hertel, S.; Knight, W. H.; Paterson,
J . Synth. Commun. 1988, 18, 2225-2231.
(16) Lubell, W. D.; Rapoport, H. J . Am. Chem. Soc. 1988, 110, 7447-
7455.
(17) Tamaki, K.; Tanzawa, K.; Kurihara, S.; Oikawa, T.; Monma,
S.; Shmada, K.; Sugimura, Y. Chem. Pharm. Bull. 1995, 43, 1883-
1893.
(18) Nugiel, D. A.; J acobs, K.; Decicco, C. P.; Nelson, D. J .; Copeland,
R. A.; Hardman, K. D. Bioorg. Med. Chem. Lett. 1995, 5, 3053-3056.
(19) Carpino, L. A.; Mansour, E.-S. M. E.; Sadat-Aalaee, D. J . Org.
Chem. 1991, 56, 2611-2614.
59-61 °C; [R]25 -13.9° (c 0.098); IR (Nujol) 1366, 1542, 1701,
D
1
1718, 3304 cm-1; H NMR δ 0.78 (d, 3H, J ) 6.8), 1.01 (d, 3H,
1736 J . Org. Chem., Vol. 69, No. 5, 2004

J ) 6.5), 1.08 (t, 3H, J ) 7.4), 1.44 (s, 9H), 2.19 (m, 1H), 2.51
(m, 2H), 4.28 (m, 1H), 5.15 (br d, 1H); 13C NMR δ 7.7, 16.8, 19.9,
28.4 (3 C’s), 30.5, 34.0, 63.9, 79.7, 156.1, 210.3. Anal. Calcd for
C12H23NO3: C, 62.61; H, 10.43; N, 6.09. Found: C, 62.77; H,
10.40; N, 6.12.
(30-50% EtOAc/hexanes) to isolate 110 mg (45%) of 17 as a clear
oil: [R]25 -25.3° (c 0.14); 1H NMR (400 MHz, CDCl3, signals
D
broadened due to hindered rotation, rotamers) δ 0.80 (m, 12H),
0.85 (m, 2H), 1.02 (t, 3H, J ) 7.2), 1.15 (m, 1H), 1.20 (m, 1H),
1.40 (s, 9H), 1.70 (m, 6H), 2.02 (m, 1H), 2.13 (m, 1H), 2.50 (m,
2H), 2.85 (m, 1H), 2.95 (m, 1H), 3.80 (m, 1H), 4.40 (m, 1H), 5.10
(m, 1H), 5.20 (m, 2H), 7.40 (m, 5H), 8.22 (d, 1H, J ) 8.4); 13C
NMR (100 MHz, CDCl3) δ 7.6, 17.8, 19.6, 19.9, 20.1, 22.5, 22.9,
28.2, 28.3 (3C), 29.6, 30.0, 34.0, 36.3, 37.3, 37.5, 46.0, 57.9, 63.5,
68.9, 69.1, 80.8, 128.2 (2C) 128.5, 128.8 (2C), 157.5, 170.9, 172.2,
179.8, 210.0; HRMS m/z calcd for C33H52N3O7 (M + H)+
602.3805, found 602.3795.
(S)-4-Am in o-5-m et h yl-3-h exa n on e Hyd r och lor id e (14).
To a solution of BOC-protected amino ketone 13 (0.5 g, 2.2 mmol)
in dioxanes (10 mL) was added a 3.6 M solution of HCl in
dioxanes at rt in one portion. The mixture was stirred at rt for
6 h, then an additional 2 mL of 3.6 M HCl in dioxanes was added,
and stirring was continued at rt for 48 h. Excess solvent was
removed under reduced pressure, and the resulting solid was
suspended in hexanes, filtered, and dried to give the desired
amino ketone 14 (360 mg, 83%) as a white solid: mp 136-141
(âR,6S)-Tetr a h yd r o-â-(3-m eth ylbu tyl)-6-[[[(1S)-1-(m eth -
ylet h yl)-2-oxob u t yl]a m in o]ca r b on yl]- γ-oxo-2-[(p h en yl-
m eth oxy)ca r bon yl]-1(2H)-p yr id a zin ebu ta n oic Acid (18).
To tert-butyl ester 17 (110 mg, 1.8 mmol) in CH2Cl2 (15 mL)
was added 0.25 mL (3.3 mmol) of trifluoroacetic acid. This
mixture was heated at reflux for 2 h and cooled, then more
trifluoroacetic acid (0.25 mL) was added, and reflux was
continued for 4 h. This addition and heating sequence was
repeated two more times, then the reaction was cooled, and the
volatiles were removed under reduced pressure to give an oil.
This oil was partitioned between EtOAc and saturated aqueous
NaHCO3. The organic layer was separated, washed with brine,
dried, filtered, and concentrated to give 80 mg (80%) of 18 as
°C; [R]25 +37.8° (c 0.12); IR 1522, 1593, 1724 cm-1 1H NMR
;
D
(DMSO-d6) δ 0.89 (d, 3H, J ) 6.9), 0.99 (m, 6H), 2.32 (m, 1H),
2.64 (q, 2H, J ) 7.2), 3.99 (d, 1H, J ) 4.1), 8.5 (br s, 3H); 13C
NMR (DMSO-d6) δ 5.7, 15.7, 17.3, 26.9, 31.9, 61.1, 205.6.
1,1-Dim et h ylet h yl (3R)-3-(F lu or oca r b on yl)-6-m et h yl-
h ep ta n oa te (15). To a solution of succinate 5 (700 mg, 2.9
mmol) stirring in CH2Cl2 (10 mL) was added pyridine (0.24 mL,
2.9 mmol). This stirred mixture was cooled to 5 °C, and then
cyanuric fluoride (1.25 mL, 15.0 mmol) was added in one portion.
A white precipitate formed which slowly dissolved, and then a
second precipitate formed. The suspension was then allowed to
stir at rt for 18 h. The reaction mixture was filtered through a
fine frit funnel, and the solid was rinsed with CH2Cl2. The
filtrate was partitioned between CH2Cl2 and chilled water. The
organic layer was separated and washed with brine, dried,
filtered, and concentrated to give the acid fluoride 15 (650 mg,
an oil which solidified upon standing: mp 116-120 °C; [R]25
D
-23.5° (c 0.35); IR (neat) 1404, 1706, 2960, 3400 cm-1; 1H NMR
δ 0.80 (m, 12H), 1.02 (m, 3H), 1.15 (m, 2H), 1.20 (m, 2H), 1.45
(m, 1H), 1.70 (m, 3H), 2.13 (m, 1H), 2.50 (m, 3H), 2.85-2.95 (m,
2H), 3.65 (m, 1H), 4.15 (m 1H), 4.40 (m, 1H), 4.60 (m 1H), 4.96
(m, 1H), 5.20 (m, 2H), 7.36 (m, 5H), 8.15 (d, 1H); 13C NMR δ
7.5, 17.6, 19.6, 19.8, 22.4, 22.7, 23.4, 28.1, 29.4, 30.0, 33.9, 35.7,
36.1, 37.5, 46.0, 58.5, 63.6, 69.1, 128.2 (2C), 128.4, 128.8 (2C),
135.5, 157.8, 171.4, 176.6, 179.9, 209.9; MS AP(+) m/z 546.12
(M + H)+, AP(-) m/z 544.04 (M - H)-; HRMS m/z calcd for
C29H44N3O7 (M + H)+ 546.3179, found 546.3168.
1
91%) as an oil: IR (neat) 1730, 1838 cm-1; H NMR δ 0.85 (d,
6H, J ) 6.6), 1.18 (m, 2H), 1.39 (s, 9H), 1.55 (m, 3H), 2.50 (m,
1H), 2.59 (m, 1H), 2.95 (m, 1H); 19F NMR (282.2 MHz) δ 38.39
(s).
1-(2-P h en ylm et h yl) Hyd r ogen (3S)-2-(2R)-2-[2-(1,1-d i-
m eth yleth oxy)-2-oxoeth yl]-5-m eth yl-1-oxoh exyl] Tetr a h y-
d r o-1,3(2H)-p yr id a zin ed ica r boxyla te (16). To 480 mg (1.8
mmol) of (3S)-N-Cbz-piperazic acid (9) in CH2Cl2 (20 mL) was
added N,N-diisopropylethylamine (410 µL, 2.5 mmol) in one
portion followed by a solution of acid fluoride 15 (450 mg, 1.8
mmol) in CH2Cl2 (10 mL). The resulting solution was stirred at
rt for 56 h and then heated to 45 °C for 1 h. The mixture was
cooled to rt and then partitioned between CH2Cl2 and water.
The organic layer was separated, washed with water and brine,
dried, filtered, and concentrated to give a crude oil (760 mg).
This oil was purified by silica gel chromatography (1-5% AcOH
in 1:1 hexanes/EtOAc) to isolate amide 16 (300 mg, 34%) as an
(âR,6S)-Tetr a h yd r o-â-(3-m eth ylbu tyl)-6-[[[(1S)-1-(m eth -
ylet h yl)-2-oxob u t yl]a m in o]ca r b on yl]-γ-oxo-1(2H )-p yr id -
a zin ebu ta n oic Acid (1). Acid 18 (70 mg, 1.3 mmol) in methanol
(10 mL) was combined with 70 mg of 10% palladium on carbon
at rt under a blanket of nitrogen. A balloon of hydrogen was
placed over the reaction mixture, and it was stirred for 6 h. The
reaction was purged with nitrogen and filtered through a pad
of Celite, rinsing with methanol. The solvent was removed under
reduced pressure to give an oil that was purified by silica gel
chromatography (1-5% AcOH in 1:1 hexanes/EtOAc) to give the
desired product 1 as an oil (50 mg, 94%): [R]25 -22° (c 0.051);
D
oil: [R]26 -20.6° (c 0.081); IR (neat) 1720, 1722, 3100 cm-1; 1H
1H NMR δ 0.71 (d, 3H, J ) 6.6), 0.77 (d, 6H, J ) 6.6), 0.88 (d,
2H, J ) 6.6), 1.01 (t, 3H, J ) 7.5), 1.11 (m, 2H), 1.43 (m, 6H),
2.0 (m, 1H), 2.15 (m, 2H), 2.41 (m, 3H), 2.75 (m, 2H), 2.94 (d,
1H, J ) 11.9), 3.76 (m, 1H), 4.50 (m, 2H), 5.19 (m, 1H), 6.86 (d,
1H, J ) 8.4); 13C NMR δ 7.7, 17.2, 20.1, 21.1, 22.4, 22.8, 25.9,
28.1, 30.1, 30.3, 34.2, 35.9, 36.3, 36.5, 47.3, 50.8, 62.7, 172.1,
177.0, 178.1, 209.8; HRMS m/z calcd for C21H38N3O5 (M + H)+
412.2726, found 412.2812.
D
NMR (signals broadened due to hindered rotation) δ 0.80 (m,
6H), 1.15 (m, 2H), 1.27 (m, 2H), 1.39 (m, 11H), 1.70 (m, 2H),
1.95 (m, 3H), 2.39 (dd, 1H, J ) 3.6, 16.9), 2.70 (m, 1H), 3.10 (m,
1H), 3.80 (m, 1H), 4.10 (m, 1H), 5.21 (d, 2H, J ) 13), 7.35 (m,
5H); 13C NMR (CDCl3) δ 20.1, 22.3 (2C), 22.8, 23.3, 28.0, 28.2
(3C), 29.3, 36.1, 37.0, 37.3, 46.0, 56.1, 69.7, 80.9, 128.6 (2C),
128.8 (2C), 135.0, 159.0, 171.7, 172.2, 179.7. Anal. Calcd for
C26H38N2O7: C, 63.65; H, 7.81; N, 5.71. Found: C, 63.40; H, 7.83;
N, 5.50.
Ack n ow led gm en t . We thank Dr. Steven F.
Cheatham and Mr. Michael Kline for NMR spectroscopy
and Dr. Susanta Samajdar (Biocon, Ltd.) for synthesis
of phenylalanine amides and optical purity studies of 5
and 9.
1,1-Dim eth yleth yl (âR,6S)-tetr a h yd r o-â-(3-m eth ylbu tyl)-
6-[[[(1S)-1-(m et h ylet h yl)-2-oxob u t yl]a m in o]ca r b on yl]-γ-
oxo-2-[(p h en ylm eth oxy)ca r bon yl]-1(2H)-p yr id a zin ebu ta n -
oa te (17). To 200 mg (0.40 mmol) of piperazic acid 16 stirring
in 8 mL of a 3:1 mixture of THF/DMF was added 170 µL (1.2
mmol) of triethylamine in one portion. This mixture was cooled
to 0 °C, and then the amino ketone hydrochloride 14 (200 mg,
1.2 mmol) was added in one portion, followed by diethyl
phosphorylcyanidate (190 µL, 1.2 mmol) in one portion. The
mixture was allowed to warm to rt, stirred for 16 h, and then
partitioned between EtOAc and H2O. The organic layer was
separated, washed with brine, dried, filtered, and concentrated
to give an oil. This oil was purified by silica gel chromatography
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
cedures for compounds 2-5 and 9-11, optical purity deter-
mination of compounds 5 and 9, and a table of 1H and 13C NMR
spectroscopic data for comparison of the data of synthetic 1 to
the data reported for the natural product (PDF). This material
is available free of charge via the Internet at http://pubs.acs.org.
J O035667T
J . Org. Chem, Vol. 69, No. 5, 2004 1737