Synthesis of antimalarial compounds fosmidomycin and FR900098 through N- or P-alkylation reactions

Article abstract of DOI:10.1016/j.tet.2012.11.049

Two straightforward and convenient routes for the synthesis of the antimalarial agents FR900098 and fosmidomycin are described. In the key steps N- or P-alkylation reactions are used. The best overall yields of FR900098 and fosmidomycin in 15 mmol scale a

Full text of DOI:10.1016/j.tet.2012.11.049

Tetrahedron 69 (2013) 1183e1188
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Tetrahedron
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Synthesis of antimalarial compounds fosmidomycin and FR900098
through N- or P-alkylation reactions
*
Surisetti Suresh, Dharavath Shyamraj, Mats Larhed
Organic Pharmaceutical Chemistry, Department of Medicinal Chemistry, Uppsala University, BMC, Box 574, SE-751 23 Uppsala, Sweden
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 June 2012
Received in revised form 25 October 2012
Accepted 13 November 2012
Available online 20 November 2012
Two straightforward and convenient routes for the synthesis of the antimalarial agents FR900098 and
fosmidomycin are described. In the key steps N- or P-alkylation reactions are used. The best overall yields
of FR900098 and fosmidomycin in 15 mmol scale are 83% and 68%, respectively. These routes utilize
readily available materials and avoid harsh conditions.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Fosmidomycin
FR900098
N-alkylation
P-alkylation
1. Introduction
Mtb and Pf with IC50 values of 160 nM and 18 nM, respectively.6
Furthermore, FR900098 is an effective antimalarial agent in ani-
Tuberculosis (tb) and malaria are two of the epidemic diseases
that cause the highest mortality rates on the globe. According to the
most recent WHO report as many as 9 million people were infected
by active tb and 250 million people were infected by malaria in
2010.1 Further, due to tb and malaria infection about 1.4 million and
1 million deaths occurred, respectively.1 The causative agent of tb is
the pathogenic bacteria Mycobacterium tuberculosis (Mtb). The
emergence of multi-drug-resistant M. tuberculosis strains and the
lack of any new antituberculosis agent in the last 45 years highlight
the need for the development of new therapies. Human malaria is
caused by four species of the protozoa family Plasmodium, Plas-
modium falciparum (Pf), Plasmodium malariae (Pm), Plasmodium
ovale (Po) and Plasmodium vivax (Pv). Pf is responsible for the
greatest number of deaths and has been the subject of most sci-
entific investigations. Both these microorganisms, Mtb and Pf, use
the non-mevalonate pathway for the biosynthesis of essential
mal models and has shown promise in early human trials with
effect against drug-resistant strains.7 Additionally, FR900098 has
a low toxicity profile.
In spite of its promising properties in drug development efforts
against tb and malaria, there have been only a limited number re-
ported methods for the total synthesis of FR900098.8e17 In these
reports alkylation and reductive amination8,10e17 or nitroso-ene
reactions were used as key steps and the best overall yield was
64%.9 We have taken research efforts to further develop the syn-
thesis of FR900098 and fosmidomycin with the objectives (a) to
improve overall yield, (b) to identify mild conditions and avoid
toxic reagents. We hereby report two efficient synthetic routes on
15 mmol scale to afford FR900098, including all experimental de-
tails and with full characterization of all key intermediates.
isoprenoids.2 1-Deoxy-
(DXR) is the second enzyme in the non-mevalonate pathway, which
converts 1-deoxy- -xylulose-5-phosphate (DXP) to 2-C-methyl-D-
D-xylulose-5-phosphate reductoisomerase
2. Results and discussion
D
We envisaged the synthesis of FR900098 and fosmidomycin via
a simple and systematic protectionealkylationedeprotection strat-
egy. A retrosynthetic analysis of FR900098 and fosmidomycin is
depicted in Scheme 1. Intermediate A, in which phosphonic acid and
hydroxylamine functionalities are protected, could easily be obtained
from benzyloxyamine B that in turn might be prepared from Boc
protected C. The intermediate C could either be synthesized through
the N-alkylation reaction of D and alkyl bromide E, or through the P-
alkylation reaction of phosphite F and alkyl bromide G.
erythritol 4-phosphate (MEP). Since the non-mevalonate pathway
is absent in humans, DXR has become an attractive target for an-
timicrobial drug discovery.3e5 FR900098, a close analog of the
naturally occurring antibiotic fosmidomycin, inhibits the DXR of
* Corresponding author. Tel.: þ46 18 471 4667; fax: þ46 18 471 4474; e-mail
addresses: Mats.Larhed@orgfarm.uu.se, Larhed@orgfarm.uu.se (M. Larhed).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.11.049

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S. Suresh et al. / Tetrahedron 69 (2013) 1183e1188
in turn reduce one step in the total synthesis by the simultaneous
deprotection of benzyl groups of both the phosphonate and the
hydroxamic acid functionalities. Accordingly, we prepared dibenzyl
3-bromopropylphosphonate from the reaction of dibenzyl phos-
phonate with 1,3-dibromopropane in the presence of sodium hy-
dride but the desired compound was obtained only in moderate
yield (60%). Thus, we decided to proceed through initial N-alkyl-
ation followed by P-alkylation as shown in Scheme 3. We initially
attempted to prepare alkyl bromide 7 from the reaction of 2
(15 mmol) with excess 1,3-dibromopropane (4 equiv), in the
presence of sodium hydride (1 equiv). Under these reaction con-
ditions intermediate 7 was obtained in 91% isolated yield. Then
compound 7 was subjected to P-alkylation using dibenzyl phos-
phonate to furnish the fully protected compound 8 in excellent
isolated yield (92%). It was realized that lower amounts of TFA
(180 mmol,14 mL) and shorter reaction time (1 h) were required for
the deprotection of the Boc group in intermediate 8 when com-
pared to that in compound 3 (460 mmol, 35 mL, 7 h). Excess TFA
and longer reaction times resulted in the hydrolysis of dibenzyl
phosphonate group that in turn lowered the isolated yield of
phosphonate ester 9. In the next step, compound 9 was acetylated
to furnish the protected form of FR900098 (10) in 94% isolated
yield. The benzyl protected compound 10 was then subjected to Pd/
C catalyzed hydrogenation followed by aq NaOH treatment to af-
ford the target compound FR900098. An overall yield of 67% was
realized through this six-step 15 mmol scale synthesis.
Scheme 1. Retrosynthetic plan for FR900098 and fosmidomycin.
We have conducted the reactions involving N-alkylation as a key
step on a 15 mmol scale as shown in Scheme 2. Initially, diethyl 3-
bromopropylphosphonate 1 was reacted with N- and O-protected
hydroxylamine 2 (15 mmol) in the presence of sodium hydride
(1 equiv) to give compound 3 in an excellent isolated yield of 96%.
Subsequently compound 3 was treated with trifluoroacetic acid to
liberate nucleophilic amine 4, which was acetylated to obtain the
key intermediate 5 in quantitative yield that obviated column
chromatography. Pd/C catalyzed hydrogenation of 5 furnished
debenzylated 6 in again quantitative yield, which did not require
further purification. FR900098 was then prepared from 6, using
TMSBr-mediated hydrolysis of phosphonate followed by treatment
with aq NaOH. It is important to note that the antimalarial agent
FR900098 was synthesized through this six-step route in an overall
yield of 83%, whereas the same procedure on a 1 mmol scale gave
82% isolated yield.18
Next it was decided to avoid the use of reactive TMSBr, which is
used in the hydrolysis of diethyl phosphonate group, by the utili-
zation of the dibenzyl phophonate moiety in its place, which would
Scheme 3. Synthesis of FR900098 (15 mmol scale) through P-alkylation as a key step.
We became interested in evaluating the N-alkylation strategy
also for 15 mmol scale synthesis of fosmidomycin as illustrated in
Scheme 4. The intermediate 4 (15 mmol) was subjected to for-
mylation using 2 equiv of CDI in the presence of formic acid to af-
ford formamide 11 (92%), which was in turn subjected to Pd/C
catalyzed hydrogenation to obtain compound 12 in 91% yield.
TMSBr-mediated hydrolysis of the diethyl phosphonate furnished
fosmidomycin in good yield. The overall yield of 1 to fosmidomycin
through this route was 68%, whereas in an otherwise identical
1 mmol scale reaction route, the yield was 73%.
We finally synthesized fosmidomycin also through the P-alkyl-
ation route (Scheme 5). Intermediate 9 was treated with CDI and
formic acid to give formylated product 13 that was subjected to Pd/
C catalyzed hydrogenation followed by the treatment with 1 N
NaOH to provide the required fosmidomycin in disappointing 27%
overall yield over six steps.
Scheme 2. Synthesis of FR900098 (15 mmol scale) through N-alkylation as a key step.

S. Suresh et al. / Tetrahedron 69 (2013) 1183e1188
1185
Compound 3, 7, 8,11, and 13 are newsubstances. All final compounds
were ꢁ95% pure as determined by LCeMS, NMR and HPLCeUV.
4.2. Preparation of tert-butyl benzyloxy(3-(diethox-
yphosphoryl)propyl)carbamate (3)
To a solution of tert-butyl benzyloxycarbamate 2 (14.7 mmol,
3.27 g) in anhydrous DMF (30 mL) under N2 was added sodium
hydride (60% in mineral oil, 15.2 mmol, 0.61 g) portionwise at 0 ꢂC.
After evolution of hydrogen ceased, the contents were allowed to
stir at room temperature for 1 h. Then was added diethyl (3-
bromopropyl)phosphonate (15.2 mmol, 2.92 mL) at 0 ꢂC. The re-
action mixture was stirred at room temperature for 16 h. The sol-
vent was removed on a rotavap at 60 ꢂC. Water was added to the
crude residue and extracted with EtOAc (3ꢀ200 mL). The combined
organic phase was dried over anhydrous MgSO4, filtered, and
concentrated. The crude material was purified by silica gel column
chromatography using EtOAc/methanol (100:0 to 95:5) as eluent to
obtain the desired product 3 (5.67 g, 96%) as a transparent thick oil,
Rf (10% EtOAc/isohexane) 0.45; nmax (neat) 2978, 1699, 1367, 1245,
Scheme 4. Synthesis of fosmidomycin (15 mmol scale) through N-alkylation as a key
step.
1156 cmꢃ1
; dH (400 MHz, CDCl3) 7.42e7.32 (m, 5H, Ph), 4.83 (s, 2H,
OCH2Ph), 4.15e4.00 (m, 4H, 2(OCH2Me)), 3.47 (t, J¼6.8 Hz, 2H,
CH2CH2N), 1.96e1.84 (m, 2H, PCH2CH2), 1.79e1.68 (m, 2H,
CH2CH2CH2), 1.50 (s, 9H, OCMe3), 1.30 (t, J¼7.0 Hz, 6H, 2(OCH2Me));
dC (101 MHz, CDCl3) 156.5, 135.5, 129.4, 128.5, 128.4, 81.5, 77.0, 61.5
(d, J¼6.9 Hz), 49.9 (d, J¼19.2 Hz), 28.3, 23.1 (d, J¼142 Hz), 20.5 (d,
J¼4.6 Hz), 16.4 (d, J¼6.1 Hz); MS (ESI) m/z 402 [MþH]þ; HRMS m/z
found [MþH]þ 402.2041, C19H33NO6P requires 402.2045.
4.3. Preparation of diethyl (3-((benzyloxy)amino)propyl)
phosphonate (4)
Scheme 5. Synthesis of fosmidomycin (1 mmol scale) through P-alkylation as a key
step.
3. Conclusion
To a stirred solution of TFA/DCM (35:105 mL) was added a so-
lution of 3 (14.1 mmol, 5.66 g) in DCM (10 mL) at room temperature
and stirred for 7 h. The reaction mixture was made alkaline using
saturated aq NaHCO3 at 0 ꢂC. The mixture was extracted with DCM
(2ꢀ200 mL), washed with water and brine. The organic phase was
dried over anhydrous MgSO4, filtered, and concentrated to give
compound 4 in pure form that did not require column chroma-
tography (4.15 g, 98%) as a transparent oil, Rf (95% EtOAc/MeOH)
0.27; dH (400 MHz, CDCl3) 7.35e7.26 (m, 5H, Ph), 5.58 (br s, 1H,
CH2NH), 4.68 (s, 2H, OCH2Ph), 4.15e4.00 (m, 4H, 2(OCH2Me)), 2.96
(t, J¼6.4 Hz, 2H, CH2CH2NH), 1.90e1.72 (m, 4H, PCH2CH2), 1.30 (t,
J¼7.0 Hz, 6H, 2(OCH2Me)); dC (101 MHz, CDCl3) 137.8, 128.4, 128.3,
127.8, 76.3, 61.4 (d, J¼7 Hz), 52.1 (d, J¼17 Hz), 23.2 (d, J¼141 Hz),
20.6 (d, J¼5 Hz), 16.5 (d, J¼6 Hz); MS (ESI) m/z 302 [MþH]þ.
In summary, we have developed two efficient synthetic routes
in 15 mmol scale to afford the antimalarial agent FR900098 in 83%
and 67% overall yields. Fosmidomycin was also synthesized using
N-alkylation route in 15 mmol scale with 68% and P-alkylation
route in 1 mmol scale with 27% overall yields. Notably, these pro-
cedures use mild conditions and are reported in full detail.
4. Experimental
4.1. General information
Nuclear magnetic resonance (NMR) spectra were recorded on
two instruments: 1H (at 400 MHz) and 13C (at 101 MHz). NMR
chemical shifts were reported as
d
(ppm) and referenced using the
4.4. Preparation of diethyl (3-(N-(benzyloxy)acetamido)pro-
pyl)phosphonate (5)
residual solvent signal (1H, CDCl3 at 7.26 ppm, D2O at 4.79 ppm; 13C,
CDCl3 at 77.16 ppm). Molecular mass (HR-ESI-MS) was determined
on a mass spectrometer equipped with an electrospray ion source.
To a solution of 4 (13.4 mmol, 4.04 g) in anhydrous DCM (60 mL)
was added Et3N (16.1 mmol, 2.24 mL) at 0 ꢂC under N2 atmosphere.
Then added a solution of acetyl chloride (14.8 mmol, 1.05 mL) in
anhydrous DCM (10 mL) dropwise at 0 ꢂC. The contents were
brought to room temperature and stirred overnight. The reaction
mixture was diluted in DCM (200 mL) and washed with water,
saturated aq NaHCO3, and brine. The organic phase was dried over
anhydrous MgSO4, filtered, and concentrated to give compound 5 in
pure form that did not require column chromatography (4.58 g,
99%) as a pale yellow oil, Rf (95% EtOAc/MeOH) 0.25; dH (400 MHz,
CDCl3) 7.38e7.29 (m, 5H, Ph), 4.78 (s, 2H, OCH2Ph), 4.11e3.96 (m,
4H, 2(OCH2Me)), 3.67 (t, J¼6.8 Hz, 2H, CH2CH2N), 2.05 (s, 3H,
OCMe), 1.97e1.85 (m, 2H, PCH2CH2), 1.75e1.64 (m, 2H, CH2CH2CH2),
1.26 (t, J¼7.2 Hz, 6H, 2(OCH2Me)); dC (101 MHz, CDCl3) 172.4, 134.3,
129.1, 128.9, 128.7, 76.4, 61.5, 45.4 (br), 23.0 (d, J¼142 Hz), 20.4, 20.2
(d, J¼4 Hz), 16.4 (d, J¼5 Hz); MS (ESI) m/z 344 [MþH]þ.
Analytical HPLC-MS was performed using
(50ꢀ4.6 mm) on an HPLC system (detection by UV-DAD) coupled
with quadrupole mass spectrometer (ESI-MS). Analytical
a C18 column
a
UHPLCeMS was performed with an ion trap mass spectrometer
and UV-DAD detection using a C18 column (50ꢀ3 mm). Acetonitrile
or methanol with 0.05% aq formic acid was used as mobile phase at
a flow rate of 4 mL/min. Silica gel (Merck 60, 40e63 mm) was used
for flash chromatography. Analytical thin layer chromatography
was performed using aluminum sheets precoated with silica gel
(Merck, F254); detection was by UV (254 nm).
All the reagents were purchased from commercial suppliers and
used without further purification. Dichloromethane (DCM) was
freshly distilled from calcium hydride under nitrogen immediately
beforeuse. Compounds 4,19e26 5,19e21 6,9,119,23,27 10,8 FR900098,8e17
12,11,12,28,29 and fosmidomycin10e14,30e39 are known structures.

1186
S. Suresh et al. / Tetrahedron 69 (2013) 1183e1188
4.5. Preparation of diethyl (3-(N-hydroxyacetamido)propyl)
phosphonate (6)
CDCl3) 7.38e7.27 (m, 15H, 3(Ph)), 5.07e5.01 (m, 2H, OCH2Ph),
4.98e4.92 (m, 2H, OCH2Ph), 4.79 (s, 2H, OCH2Ph), 3.46e3.41 (m, 2H,
CH2CH2N), 1.97e1.84 (m, 2H, PCH2CH2), 1.84e1.72 (m, 2H,
CH2CH2CH2), 1.49 (s, 9H, OCMe3); dC (101 MHz, CDCl3) 156.5, 136.4,
136.4, 135.4, 129.4, 128.6, 128.5, 128.4, 128.4, 127.9, 81.5, 77.0, 67.1
(d, J¼7 Hz), 49.9 (d, J¼20 Hz), 28.3, 23.5 (d, J¼141 Hz), 20.4 (d,
J¼5 Hz); MS (ESI) m/z 526 [MþH]þ; HRMS m/z found [MþH]þ
526.2361, C29H37NO6P requires 526.2358.
To a solution of 5 (13.0 mmol, 4.47 g) in methanol (30 mL) was
added 10% Pd/C (234 mg) at room temperature carefully. The air
was exchanged with nitrogen in three cycles. The reaction mixture
was evacuated for 2e5 s with stirring. The contents were then
stirred under the atmosphere of hydrogen at room temperature for
4 h. The reaction mixture was filtered over a pad of Celite and
washed with methanol. The filtrate was concentrated to give
compound 6 in pure form that did not require column chroma-
tography (3.28 g, 99%) as a pale yellow oil, Rf (10% EtOAc/isohexane)
0.12; dH (400 MHz, CDCl3) 9.73 (br s, 1H, NOH), 4.05e3.90 (m, 4H,
2(OCH2Me)), 3.61 (t, J¼6.2 Hz, 2H, CH2CH2N), 2.05 (s, 3H, OCMe),
1.91e1.77 (m, 2H, PCH2CH2), 1.77e1.65 (m, 2H, CH2CH2CH2), 1.23
(t, J¼7.0 Hz, 6H, 2(OCH2Me)); dC (101 MHz, CDCl3) 172.3, 61.9
(d, J¼6 Hz), 47.6 (d, J¼14 Hz), 22.3 (d, J¼141 Hz), 20.4, 19.4
(d, J¼5 Hz), 16.3 (d, J¼6 Hz); MS (ESI) m/z 254 [MþH]þ.
4.9. Preparation of dibenzyl (3-((benzyloxy)amino)propyl)
phosphonate (9)
To a stirred solution of TFA/DCM (14:70 mL) was added a solu-
tion of 8 (12.0 mmol, 6.31 g) in DCM (10 mL) at room temperature
and stirred for 1 h. The reaction mixture was made alkaline using
saturated aq NaHCO3 at 0 ꢂC. The mixture was extracted with DCM
(2ꢀ200 mL), washed with water and brine. The organic phase was
dried over anhydrous MgSO4, filtered, and concentrated to give
compound 9 in pure form that did not require column chroma-
tography (4.70 g, 92%) as a transparent oil, Rf (10% EtOAc/isohexane)
0.42; dH (400 MHz, CDCl3) 7.38e7.26 (m, 15H, 3(Ph)), 5.51 (br s, 1H,
CH2NH), 5.09e5.01 (m, 2H, OCH2Ph), 4.99e4.92 (m, 2H, OCH2Ph),
4.64 (s, 2H, OCH2Ph), 2.91 (t, J¼6.2 Hz, 2H, CH2CH2N), 1.88e1.74 (m,
4H, PCH2CH2); dC (101 MHz, CDCl3) 137.8, 136.5, 136.4, 128.6, 128.4,
128.4, 127.9, 127.8, 76.3, 67.1 (d, J¼7 Hz), 52.0 (d, J¼17 Hz), 23.6 (d,
J¼141 Hz), 20.5 (d, J¼4 Hz); MS (ESI) m/z 426 [MþH]þ; HRMS m/z
found [MþH]þ 426.1839, C24H29NO4P requires 426.1834.
4.6. Preparation of sodium hydrogen(3-(N-hydrox-
yacetamido)propyl)phosphonate (FR900098)
Reported procedure was followed. Compound 6 of 3.24 g
(12.8 mmol) was used as substrate. Yield 90% (2.52 g).9
4.7. Preparation of tert-butyl benzyloxy(3-bromopropyl)car-
bamate (7)
To a solution of tert-butyl benzyloxycarbamate 2 (15.0 mmol,
3.35 g) in anhydrous DMF (30 mL) under N2 was added sodium
hydride (60% in mineral oil, 15.5 mmol, 0.62 g) portionwise at 0 ꢂC.
After evolution of hydrogen ceased, the contents were allowed stir
at room temperature for 1 h. Then was added 1,3-dibromopropane
(60.0 mmol, 6 mL) once at 0 ꢂC. The reaction mixture was stirred at
4.10. Preparation of dibenzyl (3-(N-(benzyloxy)acetamido)
propyl)phosphonate (10)
To a solution of 9 (11.0 mmol, 4.68 g) in anhydrous DCM (50 mL)
was added Et3N (13.2 mmol, 1.85 mL) at 0 ꢂC under N2 atmosphere.
Then added a solution of acetyl chloride (12.1 mmol, 1.68 mL) in
anhydrous DCM (10 mL) dropwise at 0 ꢂC. The contents were
brought to room temperature and stirred overnight. The reaction
mixture was diluted in DCM (200 mL) and washed with water,
saturated aq NaHCO3, and brine. The organic phase was dried over
anhydrous MgSO4, filtered, concentrated, and passed through silica
column using EtOAc as eluent to give compound 10 (4.83 g, 94%) as
a pale yellow oil, Rf (95% EtOAc/MeOH) 0.50; dH (400 MHz, CDCl3)
7.37e7.26 (m, 15H, 3(Ph)), 5.06e5.00 (m, 2H, OCH2Ph), 4.98e4.91
(m, 2H, OCH2Ph), 4.74 (s, 2H, OCH2Ph), 3.65 (t, J¼6.6 Hz, 2H,
CH2CH2N), 2.05 (s, 3H, OCMe), 1.97e1.85 (m, 2H, PCH2CH2),
1.80e1.70 (m, 2H, CH2CH2CH2); dC (101 MHz, CDCl3) 172.3, 136.4,
136.3, 134.3, 129.2, 129.0, 128.7, 128.6, 128.4, 127.9, 76.4, 67.2 (d,
J¼6 Hz), 45.3, 23.4 (d, J¼141 Hz), 20.5, 20.2 (d, J¼5 Hz); MS (ESI) m/z
468 [MþH]þ.
room temperature for 16 h. The solvent was removed on a rotavap
ꢂ
at 60 C. Water was added to the reaction mixture and extracted
with EtOAc (3ꢀ200 mL). The combined organic phase was dried
over anhydrous MgSO4, filtered, and concentrated. The crude ma-
terial was purified by silica gel column chromatography using
isohexane/EtOAc (100:0 to 98:2) as eluent to obtain the desired
product 7 (4.71 g, 91%) as a transparent oil, Rf (10% EtOAc/iso-
hexane) 0.50; nmax (neat) 2976, 1700, 1366, 1253, 1153 cmꢃ1
; dH
(400 MHz, CDCl3) 7.35 (s, 5H, Ph), 4.84 (s, 2H, OCH2Ph), 3.56
(t, J¼6.6 Hz, 2H, BrCH2CH2), 3.40 (t, J¼6.5 Hz, 2H, CH2CH2N), 2.12
(quin, J¼6.6 Hz, 2H, CH2CH2CH2), 1.51 (s, 9H, OCMe3); dC (101 MHz,
CDCl3) 156.4, 135.4, 129.4, 128.6, 128.5, 81.6, 76.9, 48.1, 30.8, 30.4,
28.3; MS (ESI) m/z 344 [MþH]þ; HRMS m/z found [MþH]þ
344.0859, C15H2379BrNO3 requires 344.0861.
4.8. Preparation of tert-butyl benzyloxy(3-(bis(benzyloxy)
phosphoryl)propyl)carbamate (8)
4.11. Preparation of sodium hydrogen(3-(N-hydrox-
yacetamido)propyl)phosphonate (FR900098)9
To a suspension of sodium hydride (60% in mineral oil,
14.6 mmol, 0.59 g) in anhydrous DMF (30 mL) under N2 was added
dibenzyl phosphite (14.6 mmol, 3.20 mL) dropwise at 0 ꢂC. After
evolution of hydrogen ceased, the contents were allowed stir at
room temperature for 2 h. Then was added 7 (13.5 mmol, 4.65 g) in
DMF (5 mL) once at 0 ꢂC. The reaction mixture was stirred at room
temperature for 16 h. The solvent was removed on a rotavap at
60 ꢂC. Water was added to the reaction mixture and extracted with
EtOAc (3ꢀ200 mL). The combined organic phase was dried over
anhydrous MgSO4, filtered, and concentrated. The crude material
was purified by silica gel column chromatography using isohexane/
EtOAc (80:20 to 50:50) as eluent to obtain the desired product 8
(6.53 g, 92%) as a transparent thick oil, Rf (40% EtOAc/isohexane)
To a solution of 10 (10.3 mmol, 4.80 g) in methanol (30 mL) was
added 10% Pd/C (0.40 g) at room temperature carefully. The air was
exchanged with nitrogen in three cycles. The reaction mixture was
evacuated for 2e5 s with stirring. The contents were then stirred
under the atmosphere of hydrogen at room temperature for 3 h.
The reaction mixture was filtered over a pad of Celite and washed
with methanol. The filtrate was concentrated to give the acid,
which was dissolved in MeOH (15 mL) and added 6 M NaOH
(1.7 mL) dropwise. Solvent was removed under vacuum and again
dissolved in MeOH, treated with charcoal, and filtered over a pad of
Celite. The filtrate was concentrated and freeze-dried to give
FR900098 (2.10 g, 93%) as a pale brown solid, mp 187e188 ꢂC, lit.12
mp 187e188 ꢂC; nmax (neat) 2880, 1598 cmꢃ1, lit.8 nmax (KBr) 2828,
1634 cmꢃ1 (dec); dH (400 MHz, D2O) 3.63 (t, 2H, J¼8 Hz, CH2N), 2.11
0.20; nmax (neat) 2975, 1698, 1454, 1368, 1245 cmꢃ1
; dH (400 MHz,

S. Suresh et al. / Tetrahedron 69 (2013) 1183e1188
1187
(s, 3H, CH3CO), 1.82 (m, 2H, CH2P), 1.53 (m, 2H, CH2CH2CH2); dC
(101 MHz, D2O) 173.8, 48.6 (d, J¼20 Hz, CH2N), 25.0 (d, J¼134 Hz,
PCH2), 20.4, 19.2; lit.8 dH (400 MHz, D2O) 3.65 (t, JHH¼6.6 Hz, CH2N),
2.13 (s, 3H, CH3CO), 1.82 (m, 2H), 1.55 (m, 2H, CH2P); lit.8 dC
(100 MHz, D2O) 174.2, 48.9, 25.2 (d, Jpc¼133 Hz, PCH2), 20.8, 19.5;
HRMS-FAB m/z found [MþH]þ 197.0460C5H12NO5P requires
197.0453.
The crude was evacuated overnight under high vacuum (1.88 g,
89%) as a light pink wax; dH (400 MHz, D2O) 8.08 (minor) (s, 1H,
CHO), 7.73 (major) (s, 1H, CHO), 3.40 (major) (t, J¼8 Hz, 2H,
CH2CH2N), 3.14 (minor) (t, J¼8 Hz, 2H, CH2CH2N),1.71 (t, J¼4 Hz, 2H,
PCH2CH2), 1.57e1.48 (m, J¼8 Hz, 2H, CH2CH2CH2); dC (101 MHz,
D2O) 163.7, 159.6, 50.4 (d, J¼18 Hz), 48.7, 46.7 (d, J¼19 Hz), 23.6,
22.2, 19.8 (major) (d, J¼4 Hz), 19.3 (minor) (d, J¼4 Hz); MS (ESI) m/z
184 [MþH]þ.
4.12. Preparation of diethyl (3-(N-(benzyloxy)formamido)
propyl)phosphonate (11)
4.15. Preparation of sodium hydrogen(3-(N-hydrox-
To a solution CDI (4.46 g, 27.5 mmol) in DCM (100 mL) was
added formic acid (10.4 mL, 275 mmol) dropwise under N2 atmo-
sphere at room temperature. The contents were stirred for 0.5 h
followed by the addition of 4 (4.13 g, 13.7 mmol, in 10 mL DCM) and
stirred for 2 days. The reaction mixture was diluted in DCM and
extracted. The combined organic layer was washed with brine and
dried over MgSO4 and concentrated under reduced pressure. The
crude was purified on silica gel column using EtOAc/MeOH 95:5 as
eluent to give compound 11 as a mixture of rotamers (4.14 g, 92%),
transparent thick oil, Rf (5% MeOH/EtOAc) 0.32; nmax (neat) 3387,
yformamido)propyl)phosphonate (fosmidomycin)
The crude free fosmidomycin (1.87 g, 10.2 mmol) was converted
to its mono sodium salt using the reported procedure12 to obtain
fosmidomycin (2.05 g) in 68% overall yield.
4.16. Preparation of dibenzyl (3-(N-(benzyloxy)formamido)
propyl)phosphonate (13)
2981, 1673, 1362, 1232 cmꢃ1
;
dH (400 MHz, CDCl3) 8.20 (major)
To a solution CDI (0.40 g, 2.50 mmol) in DCM (6 mL) was added
formic acid (0.38 mL, 10.0 mmol) dropwise under N2 atmosphere at
room temperature. The contents were stirred for 0.5 h followed by
the addition of 9 (0.43 g, 1.00 mmol, in 1 mL DCM) and stirred for 2
days. The reaction mixture was diluted in DCM and extracted. The
combined organic layer was washed with brine and dried over
MgSO4 and concentrated under reduced pressure. The crude was
purified on silica gel column using EtOAc/MeOH 95:5 as eluent to
give compound 13 (0.40 g, 89%) as a transparent thick oil, Rf (100%
(s, 1H, CHO), 7.98 (minor) (s, 1H, CHO), 7.37 (s, 5H, Ph), 4.96 (minor)
(s, 2H, OCH2Ph), 4.84 (major) (s, 2H, OCH2Ph), 4.08 (m, J¼8 Hz, 4H,
2(OCH2Me)), 3.64 (major) (s, 2H, CH2CH2N), 3.40 (minor) (s, 2H,
CH2CH2N), 1.99e1.89 (m, J¼8 Hz, 2H, PCH2CH2), 1.72 (t, J¼8 Hz, 2H,
CH2CH2CH2), 1.30 (t, J¼8 Hz, 6H, 2(OCH2Me)); dC (101 MHz, CDCl3)
163.3 (minor), 162.7 (major), 160.7, 134.1, 129.4, 129.1, 128.7, 128.5,
128.4, 77.8, 75.7, 62.0 (d, J¼7 Hz), 44.2 (d, J¼17 Hz), 29.6, 23.4, 22.0,
16.34 (t, J¼6 Hz); MS (ESI) m/z 330 [MþH]þ; HRMS m/z found
[MþH]þ 330.1476, C15H25NO5P requires 330.1470.
EtOAc) 0.5; nmax (neat) 3463, 3034, 2950, 1673, 1361 cmꢃ1
; dH
(400 MHz, CDCl3) 8.09 (major) (s, 1H, CHO), 7.77 (minor) (s, 1H,
CHO), 7.29e7.18 (m, 15H, 3(Ph)), 4.99e4.94 (q, J¼6 Hz, 2H, OCH2Ph),
4.89e4.84 (q, J¼6 Hz, 2H, OCH2Ph), 4.68 (s, 2H, OCH2Ph), 3.50
(major) (s, 2H, CH2CH2N), 3.21 (minor) (s, 2H, CH2CH2N), 1.82 (s, 2H,
PCH2CH2), 1.67 (s, 2H, CH2CH2CH2); dC (101 MHz, CDCl3)
163.1e136.2 (d, J¼5 Hz), 129.2, 129.1, 128.7, 128.6, 128.4, 127.9, 67.2
(d, J¼7 Hz), 44.2 (d, J¼18 Hz), 24.0, 22.6, 20.1; MS (ESI) m/z 454
[MþH]þ; HRMS m/z found [MþH]þ 454.1779, C25H29NO5P requires
454.1783.
4.13. Preparation of diethyl (3-(N-hydroxyformamido)propyl)
phosphonate (12)
To a solution of 11 (4.14 g, 12.6 mmol) in methanol (150 mL) was
added Pd/C (10%) portionwise at room temperature. The air in the
round bottom flask was exchanged with N2 (three cycles) and
evacuated for 2e5 s. Then the flask was charged with H2 and stirred
under hydrogen atmosphere for 6 h. The reaction mixture was fil-
tered on a pad of Celite and washed with methanol. The filtrate was
concentrated under reduced pressure. The crude was purified on
a silica gel column using EtOAc/MeOH 90:10 as eluent to obtain 12
as a mixture of rotamers (2.76 g, 91%), transparent thick oil, Rf (95%
EtOAc/MeOH) 0.25; dH (400 MHz, CDCl3) 9.96 (major) (s, 1H, NOH),
9.27 (minor) (s, 1H, NOH), 8.39 (major) (s, 1H, CHO), 7.88 (minor)
(s, 1H, CHO), 4.12e4.01 (m, J¼4 Hz, 4H, 2(OCH2Me)), 3.65 (major)
(t, J¼6 Hz, 2H, CH2CH2N), 3.58 (minor) (t, J¼6 Hz, 2H, CH2CH2N),
2.06e1.90 (m, J¼6 Hz, 2H, PCH2CH2), 1.84e1.71 (m, J¼6 Hz, 2H,
CH2CH2CH2), 1.31 (t, J¼6 Hz, 6H, 2(OCH2Me)); dC (101 MHz, CDCl3)
163.4 (major) 158.1 (minor), 62.3 (major) (d, J¼7 Hz), 61.8 (minor)
(d, J¼7 Hz), 49.0 (minor) (d, J¼12 Hz), 46.3 (major) (d, J¼7 Hz), 22.5
(d, J¼141 Hz), 20.1 (minor) (d, J¼5 Hz), 18.6 (major) (d, J¼5 Hz), 16.4
(minor) (d, J¼6 Hz), 16.3 (major) (d, J¼6 Hz); MS (ESI) m/z 240
[MþH]þ; HRMS m/z found [MþH]þ 240.0999, C8H19NO5P requires
240.1001.
4.17. Preparation of sodium hydrogen(3-(N-hydrox-
yformamido)propyl)phosphonate (fosmidomycin)
To a solution of 13 (0.32 g, 0.70 mmol) in methanol was added
Pd/C (10%) portionwise at room temperature. The air in the round
bottom flask was exchanged with N2 (three cycles) and evacuated
for 2e5 s. Then the flask was charged with H2 and stirred under
hydrogen atmosphere for 2 h. The reaction mixture was filtered on
a pad of Celite and washed with methanol. The filtrate was con-
centrated under reduced pressure. The crude was converted to its
mono sodium salt using the reported procedure12 to obtain fos-
midomycin in pure (0.06 g, 40%) as a white powder, mp 159e161 ꢂC,
lit.12 158e160.5 ꢂC (dec); dH (400 MHz, D2O) 8.15 (minor) (s, 1H,
CHO), 7.80 (major) (s, 1H, CHO), 3.44 (major) (p, J¼8 Hz, 2H,
CH2CH2N), 2.91 (minor) (t, J¼8 Hz, 2H, CH2CH2N), 1.78e1.60 (m,
J¼8 Hz, 2H, PCH2CH2), 1.46e1.30 (m, J¼8 Hz, 2H, CH2CH2CH2); MS
(ESI) m/z 206 [MþH]þ.
4.14. Preparation of (3-(N-hydroxyformamido)propyl)phos-
phonic acid (free fosmidomycin)
To a solution of 12 (2.75 g, 11.5 mmol) in DCM (40 mL) was
ꢂ
added TMSBr (70.0 mmol) dropwise at 0 C under N2 atmosphere.
The contents were stirred at room temperature for 4 h and added
additional quota (70.0 mmol) of TMSBr at room temperature and
stirred for 4 h (reaction was monitored by LCeMS through 1 h in-
tervals). The solvent was removed and co-evaporated with CH3CN.
Acknowledgements
We gratefully acknowledge the financial support from the
Swedish Research Council and Knut and Alice Wallenberg’s
Foundation.

1188
S. Suresh et al. / Tetrahedron 69 (2013) 1183e1188
18. During the progress of this work, a similar protocol was published for the
Supplementary data
synthesis of the diisopropyl phophonate analog of intermediate 6, but without
experimental details and compound characterization data, see: Uh, E.; Jackson,
E. R.; San Jose, G.; Maddox, M.; Lee, R. E.; Lee, R. E.; Boshoff, H. I.; Dowd, C. S.
Bioorg. Med. Chem. Lett. 2011, 21, 6973e6976.
Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.tet.2012.11.049.
19. Wiesner, J.; Ortmann, R.; Jomaa, H.; Schlitzer, M. Arch. Pharm. 2007, 340,
667e669.
20. Ortmann, R.; Wiesner, J.; Reichenberg, A.; Henschker, D.; Beck, E.; Jomaa, H.;
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