Toward Orally Absorbed Prodrugs of the Antibiotic Aztreonam. Design of Novel Prodrugs of Sulfate Containing Drugs. Part 2

Article abstract of DOI:10.1021/acsmedchemlett.9b00534

Aztreonam, first discovered in 1980, is an FDA approved, intravenous, monocyclic beta-lactam antibiotic. Aztreonam is active against Gram-negative bacteria and is still used today. The oral bioavailability of aztreonam in humans is less than 1%. Herein we describe the design and synthesis of potential oral prodrugs of aztreonam.

Full text of DOI:10.1021/acsmedchemlett.9b00534

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Letter
Toward Orally Absorbed Prodrugs of the Antibiotic Aztreonam.
Design of Novel Prodrugs of Sulfate Containing Drugs Part 2
Eric M. Gordon, Matthew A. J. Duncton, Brian J Wang, Longwu Qi, Dazhong Fan, Xianfeng
Li, Zhi-Jie Ni, Pingyu Ding, Ruslan Grygorash, Eddy Low, Guijun Yu, and Jiawei Sun
ACS Med. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acsmedchemlett.9b00534 • Publication Date (Web): 08 Jan 2020
Downloaded from pubs.acs.org on January 8, 2020
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Toward Orally Absorbed Prodrugs of the Antibiotic Aztreonam. Design
of Novel Prodrugs of Sulfate Containing Drugs Part 2
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Eric M. Gordon,*,a Matthew A. J. Duncton,a Brian J. Wang,b Longwu Qi,c Dazhong Fan,c Xianfeng Li,c
Zhi-Jie Ni,c Pingyu Ding,b Ruslan Grygorash,b Eddy Low,b Guijun Yu,b and Jiawei Sunb
aArixa Pharmaceuticals, 525 University Avenue, Suite 1350, Palo Alto, CA 94301
bSynterys, Inc., 29540 Kohoutek Way, Union City, CA 94587
cAcme Bioscience, Inc., 3941 E. Bayshore Road, Palo Alto, CA 94303
KEYWORDS prodrug, sulfate, aztreonam, antibiotic.
ABSTRACT: Aztreonam, first discovered in 1980, is an FDA approved, intravenous, monocyclic beta-lactam antibiotic.
Aztreonam is active against gram-negative bacteria and is still used today. The oral bioavailability of aztreonam in human is less
than 1%. Herein we describe the design and synthesis of potential oral prodrugs of aztreonam.
Figure 1. Comparison of aztreonam and avibactam and respective
prodrugs
The inexorable rise of antibiotic resistance has forced
clinical reliance onto a small group of drugs which themselves
continue to lose efficacy. Oral antibiotics in particular, are
urgently needed to safeguard future therapeutic options,
including the ability to treat outside the hospital.1,2 Aztreonam
3 is a totally synthetic antibiotic discovered by workers at E.R.
Squibb & Sons in 1980.3-6 It is the only monocyclic beta-
lactam antibiotic approved by the FDA (1986). Aztreonam is
scientifically significant chemically in validating the
hypothesis that antimicrobial activity in beta-lactams was not
rigidly dependent upon having a second ring fused to the
monocycle as in penicillins and cephalosporins; and
biologically aztreonam was the first of several examples of
how a simple monocyclic beta-lactam when suitably equipped
with electron with-drawing N-substituents and within the
contraints imposed by other well documented binding
interactions could possess high antibiotic activity.7-10
O
O
H2N
H2N
N
N
O
S
N
O
O
O
N
O
O
O
O
S
O
O
O
OH
2
Avibactam Prodrug ARX-1796
1
Avibactam
S
S
O
O
H2N
H2N
N
N
NH
O
NH
N
O
N
O
S
N
N
-
O
SO3
X
O
O
O
CO2H
Aztreonam
CO2R
3
4
Aztreonam Prodrug design
Figure 2 shows three potential routes to key intermediate D.
Though various beta-lactam nitrogens have been sulfenylated
and tosylated, considerable efforts to sulfamylate beta-lactam
nitrogen (A) were unsuccessful.20-23 The closure of the ring via
an activated theonine hydroxyl (B), which is the method that
aztreonam is actually synthesized, led mostly to beta-
elimination to the corresponding dehydro-threonine.24,25
Aztreonam has potent activity against susceptible Gram-
negative bacteria including Pseudomonas aeruginosa,11 and
although it is nearly 40 years old, aztreonam is still used
clinically, and is noteworthy for being resistant to the growing
problem of metallo beta-lactamases. However, the drug must
be administered intravenously as the human bioavailability is
<1%.12
Recently we have reported that the beta-lactamase inhibitor
(BLI) avibactam 113,14 which has poor oral bioavailability in
man, could be converted into derivatives 2 which show high
oral bioavailability in four (4) animal species including
human.15-18 With the aim of creating an orally absorbed
prodrug of aztreonam we sought to apply the novel prodrug
design strategy previously applied to oral avibactam
prodrugs.19 Both avibactam 1 and aztreonam 3 fall into a
limited class of approved drugs containing an essential sulfate
grouping. However, the chemistry of aztreonam and
avibactam differ in that avibactam 1 has an O-sulfate group,
while aztreonam 3 has an N-sulfate group.
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crystalline amino acid 17. It was necessary to protect the acid
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of 17 as tert-butyl ester to obtain good yields in the following
N-sulfamation, which proceeds after deprotection to give acid
19, (the Cbz analog of 11a). Cyclization of 19 to 20 was
carried out with TFCH as in Figure 3. Both synthetic routes to
13 were approximately equivalent in yield, and effort required,
although the route in Figure 4 could be undertaken on a larger
scale, since the starting material could be purchased on >100g
amounts.
Figure 2. Potential routes to key intermediate D.
H
BOC HN
O
S
O
N-sulfonylation
Cl
O
O
NH
O
O
A
H
OH
BOC HN
H
BOC HN
Threonine Closure
O
H
O
N
O
S
O
O
N
O
O
O
S
O
O
O
O
9
B
Figure 4. Synthesis of key intermediate 20 and 13.
D
Target
10
11
12
13
14
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H
H
BOC HN
Carbonyl - NH cyclization
O
Cbz HN (s)
(s)
Cbz HN (s)
(s)
H2
(s)
N
(s)
N
Cbz HN (s)
(s)
HN
O
H
NH2
S
O
O
O
O
N
OH
N
O
O
O
O
OH
H
SO3
SO3
17
16
15
C
14
The following describes a successful target (D) synthesis
(Figure 3). Starting with Boc-O-benzyl threonine 5, treatment
with triflic anhydride (to give 6) followed by reaction with
tetrabutylammonium azide gave 7.26 Trimethylphosphine
reduction of the azide produced amino ester 8 in 77 % yield.
N-sulfonylation with chlorosulfonate 9 to give 10 proved to be
a difficult step and even after considerable optimization using
organic solvents and bases only proceeded to sulfamate 10 in
33% yield. Subsequently, use of Schotten-Bauman conditions
greatly improved the reaction to >70% yield. Quantitative
hydrogenolysis of 10 afforded the sulfamate acid 11, which
smoothly underwent the critical cyclization with TCFH27 (80-
89%) to beta-lactam 12, the key intermediate in the overall
synthesis. As expected with an activated beta-lactam, 12a
displayed a strong 1813 cm-1 peak in the infrared spectrum.
Beta-lactams 12a-c were deprotected in high yield to give
13a-c, which are one of the two acylation precursors needed to
provide the desired target prodrugs 4.
O
S
O
O
(s)
Cbz HN
Cbz HN (s)
(s)
Cl
O
O
OH
O
H
NH2
(s)
HN
H
11a
9a
O
O
O
S
O
O
O
O
18
19
H
N
(s)
H
R
(s)
N
O
O
O
S
O
O
O
20 R= Cbz
12a R= Boc
13a R= HX
Though N-activated as beta-lactam sulfamates, both
protected intermediates 12a-c and 20 proved to be stable, well
behaved compounds. Deprotection of 12a (MsOH) led to a
purer product 13a than did hydrogenolysis of 20
(H2/Pd/MeOH) and was generally used in the balance of the
syntheses.28 In order to prepare the target prodrug double
esters, commercially available sidechain tert-butyl ester 21
was esterified on the free carboxyl with (9H-fluoren-9-
yl)methanol to give 22. The diester was treated with TFA and
from the resulting neopentyl acid 24 the ethyl ester was
prepared, and deprotected to afford 26 (Figure 5).
Figure 3. Synthesis of key intermediate 13.
OTf
OH
With the key components in hand (21, 26, 13a-c), efforts to
convert these into the target compounds were undertaken.29 To
maintain stability of the final products, the coupled materials
were kept as the TFA salts, as we observed the heteroaromatic
amine is nucleophilic enough to attack the activated beta-
lactam. Coupling of amines 13a-c (EDCI) with the individual
ester sidechains produced the final products 27-29. The tert-
butyl esters 27b, 28b, 29b were deprotected with TFA to give
free acid as TFA salts 27c, 28c, 29c in 65-71% yields over
three steps (Boc-deprotection, amide coupling and tert-butyl
ester deprotection).
(s)
Boc HN
(s)
Boc HN
(s)
(s)
Boc HN
(s)
Boc HN
(s)
(R)
(R)
H
H
H
NH2
H
N3
OBn
O
O
OBn
O
OBn
O
OBn
5
6
7
8
O
H
O
S
O
H
H
(s)
(s)
O
Boc
O
N
R
Boc HN
OH
Cl
O
OBn
O
(s)
HN
S
(s)
HN
S
O
9a
CO2CH2CH3
CH2CH2OCOC(CH3
O
O
R
R
O
)
9b
9c
3
11a
CO2CH2CH3
CH2CH2 CO2CH2CH3
10a
10b
10c
CO2CH2CH3
CH2CH2OCOC(CH3
CH2CH2OCOC(CH3
)
3
)
3
11b
11c
CH2CH2 CO2CH2CH3
CH2CH2 CO2CH2CH3
Figure 5. Preparation of sidechain esters and acylation
H
H
XH H2
N
Boc HN
(s)
(s)
(s)
(s)
N
N
O
R
O
O
O
S
S
R
O
O
O
O
13a
13b
13c
CO2CH2CH3
12a
12b
12c
CO2CH2CH3
CH2CH2OCOC(CH3
)
3
CH2CH2OCOC(CH3
)
3
CH2CH2 CO2CH2CH3
CH2CH2 CO2CH2CH3
An alternative synthetic route to an analogous Cbz-
protected version of 12 proceeded from the commercially
available amino N-sulfate 14 (Figure 4). Following formation
of the N-Cbz beta-lactam 15, desulfation with TFA afforded
16. Treatment of 16 with aqueous formic acid afforded
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OH
NH2
N
NH2
N
NH2
Supporting Information
Synthesis of intermediates and final prodrugs. Release of
aztreonam from compounds 28c and 29c using CES1. H-NMR
studies detailing the release of 3,3-dimethyltetrahydrofuran from
compound 28c when treated with CES1, and release of 5,5-
dimethyltetrahydro-2H-pyran-2-one
dimethylpentanoic acid from compound 29c when treated with
CES1.
S
S
S
N
O
O
O
O
O
O
1
2
3
4
5
6
7
8
22
OH
O
O
N
O
N
O
N
O
1
O
O
HO
24
23
21
NH2
N
NH2
N
/
5-hydroxy-4,4-
S
S
O
O
O
O
O
OH
N
N
O
O
O
O
Et
Et
25
26
The Supporting Information is available free of charge on the
ACS Publications website.
9
NH2 TFA
H
HX-H2
N
27a R1= Et, R=
27b R1= t-C(CH3
27c R1= H, R=
(s)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
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)
)
)
R=
R=
R=
CO2CH2CH3
(s)
3
3
3
S
N
O
N
O
O
H
S
R
H
Supporting information (PDF).
N
(s)
O
28a R1= Et, R=
28b R1= t-C(CH3
28c R1= H, R=
O
N
O
(s)
CH2CH2OCOC(CH3)CH3
N
O
O
S
R
O
13a
13b
13c
CO2CH2CH3
O
O
29a R1= Et, R=
29b R1= t-C(CH3
29c R1= H, R=
CH2CH2 CO2CH2CH3
O
R1
CH2CH2OCOC(CH3)CH3
CH2CH2 CO2CH2CH3
AUTHOR INFORMATION
Corresponding Author
*Eric M. Gordon Arixa Pharmaceuticals, 525 University Avenue,
Suite 1350, Palo Alto, CA 94301; emgordon@gmail.com; (650)-
465-5783.
When the fully elaborated potential prodrugs 28c and 29c
were treated with carboxyesterase 1 (CES1)30,31 both rapidly
and cleanly expelled aztreonam in high yields, with compound
28c releasing aztreonam within 2 min when incubated with
CES1 and compound 29c requiring ca. 10-20 min for maximal
release of aztreonam when incubated with CES1 (Table 1).
Hence, a mechanism as depicted in Figure 6 is proposed for
aztreonam release with both pro-moieties. In the case of 28c
the product of release besides aztreonam were 3,3-dimethyl
tetrahydrofuran (identical to an authentic sample). Esterase
Author Contributions
The manuscript was written through contributions of all authors. /
All authors have given approval to the final version of the
manuscript. / ‡These authors contributed equally. (match
statement to author names with a symbol)
cleavage
of
29c
yielded
aztreonam
/
and
5,5-
ACKNOWLEDGMENT
The authors acknowledge Charles River Laboratories (UK) for
high-resolution mass spectrometry.
dimethyltetrahydro-2H-pyran-2-one
5-hydroxy-4,4-
dimethylpentanoic (identical to an authentic sample).32
Table 1.
ABBREVIATIONS
BQL, below limits of quantification; CES1, carboxyesterase 1;
DCM,
dichloromethane;
EDCI,
1-ethyl-3-(3-
Figure 6. Mechanism of prodrug release with CES1.
dimethylaminopropyl)carbodiimide; EtOAc, ethyl acetate; MsOH,
methanesulfonic acid; TFA, trifluoroacetic acid; TCFH,
N,N,N',N'-tetramethylchloroformamidinium hexafluorophosphate;
rt, room temperature.
NH2
N
NH2
N
O
S
CO2H
28c
29c
S
+
O
O
H
N
H
N
H
H
(s)
(s)
N
O
(s)
N
N
O
(s)
N
REFERENCES
OH
O
O
O
S
+
S
X
O
O
O
O
O
O
[1] C. L. Ventola. The Antibiotic Resistance Crisis: Part 1: Causes
and Threats, Pharm. Ther., 2015, 40, 277−283.
[2] H. W Boucher, G. H. Talbot., J. S. Bradley, J. E. Edwards, D.
Gilbert, L. B. Rice, M. Scheld, B. Spellberg, J. Bartlett, Bad Bugs, No
Drugs: No ESKAPE! An Update from the Infectious Diseases Society
of America, Clin. Infect. Dis., 2009, 48, 1-12.
[3] Sykes, R. B.; Bonner, D. P.; Bush, K.; Georgopapadakou, N. H.,
Azthreonam (SQ 26,776), a Synthetic Monobactam Specifically
Active Against Aerobic Gram-negative Bacteria, Antimicrobial
Agents and Chemotherapy 1982, 21, 85-92.
[4] Cimarusti,C. M.; Bonner, D. P.; Breurer, H.; Chang, A. W.; Fritz,
A. W.; Floyd, D.M.; Kissick, T. P.; Koster, W. H.; Kronenthal, D.;
Massa, F.; Mueller, R.H.; Pluscec, J.; Slusarchyk, W. A.; Sykes, R.
B.; Taylor, M.; Weaver, E. R. 4-Alkylated Monobactams. Chiral
Synthesis and Antibiotic Activity. Tetrahedron 1983, 39, 2577-2589
and references therein.
O
HO
HO
O
O
28c
29c
Aztreonam
From progrug
From progrug
X =
X =
CO2
The rise in resistance to the antibiotics which for years were
the standards of care, has by now compromised them severely.
In recent years there have been no new safe and effective
FDA-approved oral antibiotics with broad coverage for serious
Gram-negative infections. Patients who in past years could
have been treated with oral antibiotics now have to remain in
the hospital and be treated with intravenous antibiotics.
Aztreonam, a still effective Gram-negative antibiotic, has been
used for 40 years, but its oral bioavailability of ~1% in human
has restricted its use to hospital settings. Availability of an oral
version of aztreonam could help fill an important medical need
and also reduce the cost of treatment. The potential prodrugs
of aztreonam reported herein are being evaluated for their oral
bioavailability in animals. Results of these studies will be
reported in due course.
[5] Floyd, D. M.; Fritz, W.; Cimarusti, C. M. Monobactams.
Stereospecific Synthesis of (S)-3-amino-2-oxoazetidine-1-sulfonic
Acids. J. Org. Chem. 1982, 47, 176-178.
[6] Denzel, T. W.; Cimarusti, C. M.; Singh, J.; Mueller, R. H. Process
and
Intermediates
for
Beta-Lactams
Having
Aminothiazole(iminooxyacetic acid)acetic Acid Sidechains. U.S.
Patent 5,194,604 (1993); Chem Abstr. 1992, 116, 214230 and
references therein.
ASSOCIATED CONTENT
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[7] Gordon, E. M.; Ondetti, M. A.; Pluscec, J.; Cimarusti, C. M.;
[27] Carpino, L. A.; El-Faham, A. J. Am. Chem. Soc. 1995, 117,
5401-5402 and references therein.
[28] Intermediate 19 could also be converted in to 11a. See
Supporting Information.
[29] Our choice of target prodrug for aztreonam was influenced by
our prior experience in designing oral prodrugs of avibactam. See
reference 9 for details.
[30] See Supporting Information for experimental conditions.
[31] Fukami, T.; Yokoi, T. The Emerging Role of Human Esterases.
Drug Metab. Pharmacol. 2012, 27, 466-477.
[32] See Supporting Information for experimental conditions. Several
reactions are in play in Table 1. When CES1 esterase is in high
concentrations, prodrugs are rapidly and cleanly converted to
aztreonam. Less CES1 esterase under these conditions leads to a
mixture of aztreonam and beta-lactam ring opened prodrug, which is
formed by a non-enzymatic, time dependent hydrolysis reaction. In
the control experiment, (no CES1 esterase), the products are ring
opened beta-lactam and aztreonam. This result indicates that there is a
relatively slow, non-enzymatic sulfate hydrolysis which occurs on the
prodrug under these reaction conditions.
Bonner, D. P.; Sykes, R. B. O-Sulfated. Beta-Lactam Hydroxamic
Acids (Monosulfactams). Novel Monocyclic Beta-Lactam Antibiotics
of Synthetic Origin. J. Am. Chem. Soc. 1982, 104, 6053−6060.
[8] Slusarchyk, W. A.; Dejneka, T.; Gordon, E. M.; Weaver, E. R.;
Koster, W. H. Monobactams: Ring Activating N-1 Substituents in
Monocyclic -Lactam Antibiotics. Heterocycles 1984, 21, 191-209.
[9] Sykes, R. B.; Cimarusti, C. M.; Bonner, D. P.; Bush, K.; Floyd, D.
M.; Georgopapadakou, N. H.; Koster, W. H.; Liu, W. C.; Parker, W.
L.; Principe, P. A.; Rathnum, M. L.; Slusarchyk, W. A.; Trejo, W. H.;
Wells, J. S. Monocyclic β-Lactam Antibiotics Produced by Bacteria.
Nature 1981, 291, 489-491.
[10] Imada, A.; Kitano, K.; Kintaka, K.; Muroi, M.; Asai, M.
Sulfazecin and Isosulfazecin, Novel β-Lactam Antibiotics of Bacterial
Origin. Nature 1981, 289, 590-591.
[11] Brogden, R N.; Heel, R. C. Aztreonam. Drugs 1986, 31, 96-130.
[12] Swabb, A. E. A.; Sugarman, A. A.; Stern, M. Oral
Bioavailability of the Mono-Bactam Aztreonam (SQ 26776) in
Healthy Subjects. Antimicrobial Agents and Chemotherapy 1983, 23,
548-550.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
[13] Wang, D. Y.; Abboud, M. I.; Markoulides, M. S.; Brem, J.;
Schofield, C. J. The Road to Avibactam: The First Clinically Useful
Non-β-Lactam Working Somewhat Like a β-lactam. Future Med.
Chem. 2016, 8, 1063−1084.
[14] Ball, M.; Boyd, A.; Ensor, G. J.; Evans, M.; Golden, M.; Linke,
S. R.; Milne, D.; Murphy, R.; Telford, A.; Kalyan, Y.; Lawton, G. R.;
Racha, S.; Ronsheim, M.; Zhou, S. H. Development of
a
Manufacturing Route to Avibactam, a β-Lactamase Inhibitor. Org.
Proc. Res. Develop. 2016, 20, 1799−1805.
[15] Gordon, E. M.; Duncton, M. A. J.; Gallop, M. A. Orally
Absorbed Derivatives of the β‑Lactamase Inhibitor Avibactam.
Design of Novel Prodrugs of Sulfate Containing Drugs J. Med. Chem.
2018, 61, 10340−10344.
[16] Gordon, E. M.; Freund, J.; Gallop, M. A.; Duncton, M. A. J.
Beta-Lactamase Inhibitors and Uses Thereof. U.S. Patent 1,008,5999
(2018); Chem Abstr. 2018, 169, 422442.
[17] Gordon, E. M.; Freund, J.; Gallop, M. A.; Duncton, M. A. J.
Beta-Lactamase Inhibitors and Uses Thereof. WO 208557 (2018);
Chem Abstr. 2018, 169, 512024.
[18] The results with ARX-1796 in human will be published in due
course.
[19] Gordon, E. M.; Duncton, M. A. J.; Freund, J. Aztreonam
Derivatives, Their Use in Treating Bacterial Infections and Their
Preparation. U.S. Patent 0,100,516 (2019); Chem. Abstr. 2019, 170,
463801.
[20] Woulfe, S. R.; Iwagami, H; Miller, M. J. Efficient N-
Sulfenylation of Azetidinones Using S-Substituted Thiophthalimide.
Tetrahedron Lett. 1985, 26, 3891-3894.
[21] Spillane, W.; Malaubier, J. P. Sulfamic Acid and Its N- and O-
Substituted Derivatives. Chem. Rev. 2014, 114, 2507−2586 and
references therein.
[22] Prasad, G.; Amoroso, A; Borketey, L.S.; Schnarr, N. N-Activated
β-lactams as Versatile Reagents for Acyl Carrier Protein Labeling.
Org. Biomol. Chem. 2012, 10, 1992.
[23] Jarrahpour, A.; Zarei, M. Synthesis of Novel N-Sulfonyl
Monocyclic β-Lactams as Potential Antibacterial Agents. Molecules
2006, 11, 49-58.
[24] Floyd, D. M.; Fritz, A. W.; Pluscec, J; Weaver, E. R.; Cimarusti,
C. M. Monobactams. Preparation of (S)-3-Amino-oxoazetidine-l-
sulfonic Acids From L--Amino-and Hydroxy Acids via Their
Hydroxamic Esters. J. Org. Chem. 1982, 47, 5160-5167.
[25] Miller, M. J.; Mattingly, P. G.; Morrison, M. A.; Kerwin, J. F.
Synthesis of -Lactams from Substituted Hydroxamic Acids. J. Am.
Chem. Soc. 1980, 102, 7026-7032.
[26] Martin, M. J.; Rodriguez-Acebes, R.; Garcia-Ramos, Y.;
Martinez, V.; Murcia, C.; Digon, I.; Marco, I.; Pelay-Gimeno, M.;
Fernandez, R.; Reyes, F.; Francesch, A. M.; Munt, S.; Tulla-Puche, J.;
Albericio, F.; Cuevas, C. Stellatolides, a New Cyclodepsipeptide
Family from the Sponge Ecionemia acervus: Isolation, Solid-Phase
Total Synthesis, and Full Structural Assignment of Stellatolide A. J.
Am. Chem. Soc. 2014, 136, 6754-6762.
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Table 1. Release of Aztreonam from Prodrugs using CES1.
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Timepoint after treatment with CES1a,b
Prodrug
0 min
1 min
2 min
5 min
10 min
20 min
30 min
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
27c
28c
29c
BQL
BQL
BQL
BQL
80
24
4
>95
45
8
>95
76
14
>95
86
23
>95
90
28
>95
90
a) 0.5 mg of prodrug / mL of 2.5% acetonitrile in 0.05 M citrate buffer at pH 4.7 incubated at 37 °C with 150 Units / mL of
CES1 enzyme. b) Release of aztreonam as monitored by HPLC reported at each timepoint.
TOC Graphic
NH2
N
NH2
N
S
S
O
O
O
O
CES1
H
H
H
H
N
(s)
N
(s)
N
O
(s)
N
(s)
N
N
O
OH
O
O
O
S
S
X
O
O
O
O
HO
HO
28c
29c
X = OPiv
X = CO2Et
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