Synthesis of benzyl diisopropyl 5-phosphonopentanoate and 5-phosphonopentanoic acid: An analog of succinyl phosphate

Article abstract of DOI:10.1080/10426500601013307

Benzyl 5-(diisopropoxyphosphoryl)pentanoate (benzyl diisopropyl 5-phosphonopentanoate) was synthesized from 5-bromopentanoic acid in three steps. The first step esterified 5-bromopentanoic acid with benzyl alcohol, the second step was a Finkelstein halogen exchange with sodium iodide, and the third step was a Michaelis-Arbuzov reaction. This compound was characterized by NMR and high-resolution mass spectrometry. This compound was hydrolyzed to produce 5-phosphonopentanoic acid, which is an analog of succinyl phosphate and a possible enzyme inhibitor. Copyright Taylor & Francis Group, LLC.

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Synthesis of Benzyl Diisopropyl
5-Phosphonopentanoate and 5-
Phosphonopentanoic Acid: An
Analog of Succinyl Phosphate
David R. Weyna a , David Loveless a , Cory Bottone a
, Nathan Hifko a & Christopher J. Halkides a
a Department of Chemistry and Biochemistry ,
The University of North Carolina, Wilmington ,
Wilmington, North Carolina, USA
Published online: 30 Jan 2007.
To cite this article: David R. Weyna , David Loveless , Cory Bottone , Nathan
Hifko & Christopher J. Halkides (2007) Synthesis of Benzyl Diisopropyl 5-
Phosphonopentanoate and 5-Phosphonopentanoic Acid: An Analog of Succinyl
Phosphate, Phosphorus, Sulfur, and Silicon and the Related Elements, 182:3, 563-567,
DOI: 10.1080/10426500601013307
To link to this article: http://dx.doi.org/10.1080/10426500601013307
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Phosphorus, Sulfur, and Silicon, 182:563–567, 2007
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500601013307
Synthesis of Benzyl Diisopropyl 5-Phosphonopentanoate
and 5-Phosphonopentanoic Acid: An Analog
of Succinyl Phosphate
David R. Weyna
David Loveless
Cory Bottone
Nathan Hifko
Christopher J. Halkides
Department of Chemistry and Biochemistry, The University of North
Carolina, Wilmington, Wilmington, North Carolina, USA
Benzyl 5-(diisopropoxyphosphoryl)pentanoate (benzyl diisopropyl 5-phosphono-
pentanoate) was synthesized from 5-bromopentanoic acid in three steps. The first
step esterified 5-bromopentanoic acid with benzyl alcohol, the second step was
a Finkelstein halogen exchange with sodium iodide, and the third step was
a Michaelis–Arbuzov reaction. This compound was characterized by NMR and
high-resolution mass spectrometry. This compound was hydrolyzed to produce 5-
phosphonopentanoic acid, which is an analog of succinyl phosphate and a possible
enzyme inhibitor.
Keywords Dimethylaminopyridine (DMAP); esterification; Finkelstein reaction;
Michealis–Arbuzov reaction; phosphonic acid; succinyl phosphate
INTRODUCTION
Phosphonates are commonly employed as substrate or reaction-
coordinate analogs to study enzymes catalyzing phosphoryl-group
transfer reactions. The P C bond of the phosphonate replaces the re-
active P O bond of the substrate. The goal of this study was to produce
5-phosphonopentanoic acid, which is an analog of succinyl phosphate.
Succinyl phosphate, which is a labile mixed anhydride, is thought to
Received June 26, 2006; accepted August 10, 2006.
The authors thank George Dubay (Duke University, Durham, NC) for high-resolution
mass spectrometry data.
Address correspondence to Christopher J. Halkides, Department of Chemistry and
Biochemistry, The University of North Carolina, Wilmington, Wilmington, NC 28403,
USA. E-mail: halkidesc@uncw.edu
563

564
D. R. Weyna et al.
be an intermediate in the reactions of succinyl CoA synthetase and
beta-oxoacyl-CoA transferase. Analogs of intermediates may bind more
tightly than analogs of substrates or products.1 This report is the first
synthesis of benzyl 5-(diisopropoxyphosphoryl)pentanoate of which we
are aware. 5-phosphonopentanoic acid has been synthesized previously
by a different route.2
RESULTS AND DISCUSSION
Our strategy of synthesizing 5-phosphonopentanoic acid was patterned
after the synthesis of 4-phosphonobutanoic acid (Scheme 1).3 The
synthesis of 5-phosphonopentanoic acid begins with the esterification
of 5-bromopentanoic acid with benzyl alcohol catalyzed by dimethy-
laminopyridine (DMAP).4 The next step is a Finkelstein halogen ex-
change reaction to produce benzyl 5-iodopentanoate.5 The key step is
the Michaelis–Arbuzov reaction with triisopropyl phosphite to produce
benzyl diisopropyl 5-phosphonopentanoate.6 This triester is hydrolyzed
to 5-phosphonopentanoic acid in 6 M HCl.
Table I contains high-resolution mass spectrometry data on 3. The
difference between the calculated mass of 356.1752 and the experimen-
tally observed mass of 356.1742 is −2.75 ppm. All of the chemical shifts
and coupling constants collected by 1H, 31P, and 13C NMR spectroscopy
are consistent with the identities of 3 and 4. A 31P NMR spectrum
of 4 revealed a single peak at 32.1 ppm, which is consistent with a
O
C
O
C
Br
OH
Br
OCH2Ph
1
O
O
C
OR
P
C
RO
I
OCH2Ph
OCH2Ph
2
3
O
O
C
R = 2-Pr, Et
OH
P
HO
OH
4
O
SCHEME 1

Synthesis of 5-Phosphonopentanoic Acid
565
TABLE I High-Resolution Mass Spectrometry Data for
Benzyl Diisopropyl 5-phosphonopentanoate
Calculated mass (g/mol )
Observed mass (m/z )
Error (ppm)
356.1752
356.1752
356.1752
356.1752
356.1748
356.1744
356.1744
356.1735
−1.2
−2.4
−2.4
−4.9
phosphonic acid group. Heteronuclear 31P/13C coupling constants indi-
cated that phosphorus must be coupled to the organic portion of the
product and permit assignment of the carbon nuclei. In earlier work on
the synthesis of 3, we employed triethyl phosphite, rather than triiso-
propyl phosphite, in the Arbuzov reaction. We observed a lower concen-
tration of side products when we used the latter nucleophile.
CONCLUSIONS
This work describes
a
synthesis of benzyl diisopropyl 5-
phosphonopentanoate 3, a compound that has not previously been
described. It also describes a new synthesis and more extensive
characterization of 5-phosphonopentanoic acid 4. Experiments are
underway to test the efficacy of 4 as an inhibitor of enzymes that
utilize succinyl phosphate as an intermediate, such as succinyl
CoA synthetase and beta-oxoacyl-CoA transferase. Experiments are
also underway to test this compound as an inhibitor of aspartate
semialdehyde dehydrogenase.
EXPERIMENTAL
Reactions were performed under nitrogen with oven-dried glassware.
All chemicals were reagent-grade or better and were used without fur-
ther purification unless specified. NMR spectra were recorded on a
Bruker ARX-400 spectrometer. 31P NMR spectra are referenced to phos-
phoric acid, downfield positive. 1H and 13C NMR spectra are referenced
to (CH3)4Si. Coupling constants are given in Hertz. TLC plates with a
fluorescent indicator were visualized with UV light and phosphomolyb-
date/sulfuric acid with heating. The melting point is uncorrected.
Benzyl 5-Bromopentanoate (1)
5-bromopentanoic acid (1.00 g, 5.49 mmol) and benzyl alcohol
(0.572 mL, 5.527 mmol) in 6 mL of diethyl ether were stirred at 0◦C

566
D. R. Weyna et al.
in a 50-mL round-bottom flask. A solution of dicyclohexylcarbodiimide
(1.25 g, 6.07 mmol) and DMAP (0.0338 g, 0.277 mmol) in diethyl ether
(6 mL) was added to a solution of acid and alcohol. The resulting mix-
ture was left to stir overnight and reach r.t. as the ice bath melted. The
mixture was filtered through Celite, and the filter cake was rinsed with
ether. The solution was washed with water and then 5% acetic acid. The
solution was dried with MgSO4, and the solvent was removed using ro-
tary evaporation. Proton NMR was used to identify the crude product.
Silica-gel chromatography with 2:8 ethyl acetate:hexane as the solvent
can be done to purify at this step, but this was found to be unnecessary.
Yield: 73.8%; 1H NMR (CDCl3) δ 1.78–1.92 (m, 4H, CH2C H2C H2CH2),
2.40 (t, J = 7.2 Hz, 2H, C(O)C H2CH2), 3.40 (t, J = 6.5 Hz, 2H, CH2Br),
5.12 (s, 2H, PhCH2O), 7.35 (m, 5H, Ph).
Benzyl 5-Iodopentanoate (2)
NaI (0.723 g, 4.82 mmol) was dissolved in about 4 mL of distilled,
dry acetone with stirring, and then the ester 1 (1.007 g, 3.72 mmol)
was added, causing immediate white precipitation. The reaction was
stirred overnight with minimal exposure to light. The mixture was fil-
tered through Celite and washed with dry acetone. The solvent was
removed with rotary evaporation. The product was purified by silica-
gel chromatography using 15:85 ethyl acetate:hexane. The yield was
77%; 1H NMR (CDCl3) δ 1.76–1.85 (m, 4H, CH2C H2C H2CH2), 2.39 (t,
J = 7.2 Hz, 2H, C(O)C H2CH2), 3.18 (t, J = 6.8 Hz, 2H, C H2I), 5.12 (s,
2H, PhC H2O), 7.34 (m, 5H, Ph).
Benzyl Diisopropyl 5-Phosphonopentanoate (3)
Triisopropyl phosphite was distilled under reduced pressure. Triiso-
propyl phosphite (0.719 g, 3.43 mmol) and benzyl 5-iodopentanoate
2 (1.218 g, 3.77 mmol) were combined in a round-bottom flask with
a distillation setup attached to a collection flask in dry ice. Alterna-
tively, a stream of nitrogen was flowed across the reaction in order to
remove 2-iodopropane (5). The reaction flask was placed in a sand bath
at ∼115◦C. After 4 hours and 15 minutes, the reaction was complete by
31P NMR. Silica-column chromatography with a step gradient typically
of 40:60 ethyl acetate:hexane to 60:40 ethyl acetate:hexane was used to
purify the product. Acetone/hexane solvent systems were also used for
some preparations. High-resolution mass spectrometry (Table I), proton
NMR, and phosphorus NMR were used to identify the product. Yield:
1
77.05%; 31P NMR (CDCl3) δ 30.1; H NMR (CDCl3) δ 1.29 (multiplet,
12H, C H3), 1.63–1.69 (m, 6H, CH2C H2C H2CH2), 2.38 (t, J = 7.3 Hz,

Synthesis of 5-Phosphonopentanoic Acid
567
2H, C(O)C H2), 4.66 (m, 2H, CH), 5.11 (s, 2H, PhCH2O), 7.35 m, 5H,
2
Ph); 13C NMR (CDCl3) δ 22.2 (d, JCP = 5.2 Hz, PCH2 CH2), 24.0 (s,
3
1
CH3), 25.2 (d, JPC = 18.1 Hz, PCH2CH2 CH2), 26.7 (d, JPC = 144.0
2
Hz, P CH2), 33.7 (s, HOC(O) CH2), 66.2 (s, O CH2Ph), 69.9 (d, JCP
6.7 Hz, PO CH), 128.2–135.5 (Ph), 173.1 (s, C(O)OCH2).
=
5-Phosphonopentanoic Acid
The triester 3 (0.52 g, 1.46 mmol) was added to 2 mL of constant
boiling HCl and refluxed for 72 h at 107◦C. The sample was dis-
solved twice in deionized water, and the solvent was removed by ro-
tary evaporation each time. The off-white solid was then dried in a
stream of nitrogen to remove traces of HCl and dried overnight in
vacuo over P2O5. It appeared to be pure by TLC on silica using 3:1:1
1-propanol:water:ammonia. The 1H NMR chemical shifts were in broad
agreement with a previous report, once differences in NMR solvents (d6-
DMSO versus D2O) were considered.2 Yield: 77%; m.p. 124–126.5◦C; 31
P
1
NMR (D2O) δ 32.1; H NMR (D2O) δ 1.3–1.6 (m, 6H, PCH2CH2C H2),
2.15 (t, J = 7.4 Hz, 2H, HOC(O)CH2); 13C NMR (D2O) δ 21.3 (d, 2JPC
=
3
4.7 Hz, PCH2CH2), 24.9 (d, JPC = 17.6 Hz, PCH2CH2CH2), 25.6 (d,
1JPC = 132.6 Hz, P CH2), 33.0 (HOC(O) CH2), 178.4 (HOC(O)).
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