Synthesis of phosphonocinnamic thioesters, substrate analogues of cinnamoyl-CoA reductase, a key enzyme in the lignification process

Article abstract of DOI:10.1016/S0040-4039(03)00349-6

The one-pot transesterification of diethylarylvinylphosphonates with N-acetylcysteamine has been achieved using phosphonochloridates as intermediates. Reaction of phosphonodiesters with (COCl)₂ gave the corresponding chlorinated compounds, whic

Full text of DOI:10.1016/S0040-4039(03)00349-6

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 2445–2447
Synthesis of phosphonocinnamic thioesters, substrate analogues
of cinnamoyl-CoA reductase, a key enzyme in the
lignification process
Caroline Lapeyre, Florence Bedos-Belval, Hubert Duran,* Michel Baltas and Liliane Gorrichon
SPCMIB, UMR CNRS 5068, Universite´ Paul Sabatier, 118 route de Narbonne, 31062 Toulouse, France
Received 17 January 2003; revised 23 January 2003; accepted 6 February 2003
Abstract—The one-pot transesterification of diethylarylvinylphosphonates with N-acetylcysteamine has been achieved using
phosphonochloridates as intermediates. Reaction of phosphonodiesters with (COCl)2 gave the corresponding chlorinated
compounds, which were coupled with N-acetylcysteamine in presence of Et3N. © 2003 Published by Elsevier Science Ltd.
Lignins are complex aromatic polymers resulting from
the oxidative polymerisation of hydroxycinnamyl alco-
hols, i.e. p-coumaryl, coniferyl, sinapyl alcohols.1 Their
biosynthesis begins with the common phenylpropanoid
pathway, starting by the deamination of phenylalanine
which affords p-hydroxylated cinnamic acids and next
cinnamoyl-CoA esters. They are common precursors of
a wide range of products which play important roles in
plant development and defense.2 Cinnamoyl-CoA esters
are then channelled into the lignin branch pathway to
produce the aldehydes through a reductive step involv-
ing the cinnamoyl-CoA reductase (CCR).3 The CCR
has been shown to occupy a key position as a control
point in order to regulate the carbon flux towards
lignins (Scheme 1).
activated as iminium salts before transesterification.4 In
order to investigate the mechanism and the behaviour
of the CCRs versus the three substrates (1a, 1b, 1c), we
have undertaken the synthesis of phosphorylated sub-
strates analogues.
Herein, we report a new and efficient synthetic
approach of thiophosphonates analogues 4a–d
(Schemes 2 and 3) built from the cinnamoyl pattern and
a shortened CoA frame.
Diester phosphonates (2a–2d) were obtained as previ-
ously described.5 Deprotonation of tetraethyl
methylenediphosphonate by LDA in THF gave the
corresponding anions which were condensed with the
p-hydroxycinnamic aldehydes. Thermal treatment of
the diphosphorylated intermediate gave exclusively
trans-vinylic phosphonates. The monophosphonic acids
An original way to the cinnamoyl-CoA esters has
already been proposed, in which cinnamic acids were
Scheme 1. Lignin biosynthesis pathway.
Keywords: lignification; thioesters; phosphonothioesters; cinnamoyl-CoA reductase.
* Corresponding author. Fax: +33(0)5 61 55 60 11; e-mail: huduran@chimie.ups-tlse.fr
0040-4039/03/$ - see front matter © 2003 Published by Elsevier Science Ltd.
doi:10.1016/S0040-4039(03)00349-6

2446
C. Lapeyre et al. / Tetrahedron Letters 44 (2003) 2445–2447
Scheme 2. Reagents and conditions: (i) Ref. 5; (ii) 3d, (COCl)2, then Et3N, N-acetylcysteamine, (37%).
Scheme 3. Reagents and conditions: (i) TBDPSCl, DMAP, imidazole, DMF, 16 h, rt, (67–91%); (ii) (COCl)2, CH2Cl2, 20 h, rt,
quantitative; (iii) Et3N, N-acetylcysteamine, 16 h, rt, (49–67%); (iv) Et3N–HF, THF, 15 min (23–50%).
(3a, 3d) have next been obtained by treatment of the
diesters (2a, 2d) in a basic medium (NaOH/EtOH)
under reflux (75–80% yield).
tified as the corresponding phosphonochloridate 6a (lP
27.2 ppm), 6b (29.0 ppm), 6c (23.3 ppm). Condensation
with N-acetylcysteamine in the presence of triethyl-
amine, in dichloromethane, gave the phosphono-
thioesters 4a–c (67, 49, 62%, respectively).11 Final cleav-
age of the silyl protective group has been carefully
carried out using triethylamine-HF to provide the
expected phosphonothioesters 7a–c.12
Thioesterification of 3a according to the usual carbonyl
coupling methods (EDC, HCl, DMAP, CH2Cl2)6 was
unsuccessful. Thus, several chlorination reagents
7
including POCl3 or (COCl)2 were used in order to
produce phosphonochloridates as intermediates before
coupling reactions.
In conclusion, the methodology described in this com-
munication leads to phosphonothioesters under mild
conditions, offering easy access to various thiol substi-
tutions. Efforts are underway to test the potential
inhibitor activity of these cinnamoyl-CoA analogues
versus the cinnamoyl-CoA reductase.
Treatment of phosphonodiester 2a by phosphorous
oxychloride, a reagent known to transform in one-step
under mild conditions functionalised phosphonates8
provided a complex mixture of phosphorylated com-
pounds, as evidenced by 31P NMR spectroscopy. On
the contrary, the phosphono monoacid 3d reacted with
oxalyl chloride to lead quantitatively to the correspond-
ing phosphonochloridate. This reaction was monitored
by 31P NMR spectroscopy (lP 30.63 ppm). Further
reaction with N-acetylcysteamine using triethylamine
afforded after purification the phosphonothioester 4d in
37% yield, despite a critical purification step.9
Acknowledgements
We are grateful to the ‘Centre National de la Recherche
Scientifique’ (CNRS) and the ‘Ministe`re de l’Education
Nationale de la Recherche et des Technologies’
(MENRT) for financial support. C.L. thanks the
MENRT for research grant.
Consequently, it appeared necessary to protect the p-
hydroxy group on the aromatic moiety to obtain the
phosphonothioester. The phosphonate diesters 2a–c
were
protected
by
reaction
with
tert-
References
butyldiphenylchlorosilane using imidazole, DMAP in
DMF to give compounds 5a–c in good yields (91, 67,
79%, respectively).10
1. (a) Adler, E. Wood Sci. Technol. 1977, 11, 169–218; (b)
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The silylated phosphonodiesters 5a–c were then con-
verted to the corresponding phosphonochloridates by
treatment with oxalyl chloride in dichloromethane. All
reactions have been monitored by 31P NMR spec-
troscopy and in each case a single product was iden-

C. Lapeyre et al. / Tetrahedron Letters 44 (2003) 2445–2447
2447
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3H), 4.20 (m, 2H), 6.16 (dd, J=17.2 Hz, J=23.4 Hz,
1H), 6.67 (d, J=8.2 Hz, 1H), 6.83 (dd, J=8.2 Hz, J=2.0
Hz, 1H), 6.92 (d, J=2.0 Hz, 1H), 7.17 (s, 1H), 7.38 (m,
7H), 7.69 (dd, J=7.4 Hz, J=1.2 Hz, 4H); 13C NMR (50
MHz, CDCl3), l 16.38 (d, J=6.9 Hz), 19.80 (s), 23.08 (s),
26.57 (s), 29.13 (s), 40.88 (s), 55.39 (s), 62.46 (d, J=6.7
Hz), 110.92 (s), 115.04 (d, J=155.2 Hz), 120.36 (s),
122.00 (s), 127.64 (s), 128.04 (s), 129.82 (s), 133.01 (s),
135.28 (s), 147.84 (s), 148.44 (d, J=6.3 Hz), 150.88 (s),
170.70 (s); 31P NMR (81 MHz, CDCl3), l 46.24 (s).
Selected data for 4b: Rf=0.25 (EtOAc), 1H NMR (250
MHz, CDCl3) l 1.09 (s, 9H), 1.36 (t, J=7.0 Hz, 3H), 1.98
(s, 3H), 2.94 (m, 2H), 3.48 (m, 2H), 4.18 (m, 2H), 6.16
(dd, J=17.1 Hz, J=23.5 Hz, 1H), 6.76 (d, J=8.5 Hz,
2H), 7.14 (s, 1H), 7.27 (d, J=8.5 Hz, 2H), 7.39 (m, 7H),
7.69 (d, J=7.6 Hz, 4H); 13C NMR (50 MHz, CDCl3), l
16.40 (d, J=6.5 Hz), 19.46 (s), 23.06 (s), 26.46 (s), 29.24
(s), 40.65 (s), 62.26 (d, J=6.7 Hz), 115.23 (d, J=154.0
Hz), 120.27 (s), 127.40 (d, J=23.2 Hz), 127.97 (s), 129.55
(s), 130.19 (s), 132.22 (s), 135.40 (s), 147.84 (d, J=31.4
Hz), 158.01 (s), 170.79 (s); 31P NMR (81 MHz, CDCl3),
l 46.24 (s).
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11. (a) Ingrassia, L. Thesis, University Paul Sabatier Tou-
louse III, 2000; (b) General procedure for the transesterifi-
cation as shown in Scheme 3. Synthesis of silylated
phosphonothioester 4a–d. To a solution of silylated phos-
phonodiester (1.8 mmol) in anhydrous dichloromethane
(10 mL) under a nitrogen atmosphere, was added oxalyl
chloride (8.6 mmol) and the mixture was stirred at room
temperature for 20 h. The excess of oxalyl chloride and
dichloromethane were removed under vacuum to give
quantitatively phosphonochloridate. To a solution of N-
acetylcysteamine (3.9 mmol) in dichloromethane (2 mL)
was added a mixture of previous phosphonochloridate
(1.8 mmol) and triethylamine (3.8 mmol) in
dichloromethane (1 mL). The reaction mixture was
stirred at room temperature for 16 h. Dichloromethane
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bicarbonate, then water. The organic layer was dried over
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purified by column chromatography on silica gel (eluent:
EtOAc) to provide desired product 4a (0.72 g, 67% yield),
4b (0.60 g, 49% yield), 4c (0.70 g, 62% yield), 4d (0.20 g,
37% yield).
Selected data for 4c: Rf=0.25 (EtOAc), 1H NMR (250
MHz, CDCl3) l 1.08 (s, 9H), 1.37 (t, J=7.0 Hz, 3H), 1.98
(s, 3H), 2.96 (m, 2H), 3.45 (s, 6H), 3.52 (m, 2H), 4.19 (m,
2H), 6.18 (dd, J=17.1 Hz, J=23.2 Hz, 1H), 6.58 (s, 2H),
7.16 (s, 1H), 7.33 (m, 7H), 7.68 (d, J=7.6 Hz, 4H); 13C
NMR (50 MHz, CDCl3), l 16.39 (d, J=6.9 Hz), 20.17
(s), 23.11 (s), 26.70 (s), 29.16 (s), 40.88 (s), 55.25 (s), 62.46
(d, J=7.0 Hz,), 105.06 (s), 115.20 (d, J=155.4 Hz),
126.64 (s), 127.13 (s), 129.26 (s), 134.11 (s), 135.05 (s),
148.76 (d, J=6.4 Hz), 151.12 (s), 170.70 (s); 31P NMR (81
MHz, CDCl3), l 45.96 (s).
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MHz, CDCl3) l 1.34 (t, J=7.0 Hz, 3H), 1.94 (s, 3H), 2.91
(m, 2H), 3.47 (m, 2H), 3.91 (s, 6H), 4.17 (m, 2H), 6.23
(dd, J=17.2 Hz, J=23.2 Hz, 1H), 6.82 (d, J=8.2 Hz,
1H), 7.00 (s, 1H), 7.04 (d, J=8.2 Hz, 1H), 7.23 (s, 1H)
7.38 (dd, J=17.2 Hz, J=23.6 Hz, 1H); 13C NMR (50
MHz, CDCl3), l 16.36 (d, J=6.8 Hz), 23.06 (s), 29.18 (s),
40.74 (s), 55.91 (s), 62.37 (d, J=6.9 Hz), 109.39 (s),
110.94 (s), 115.19 (d, J=155.2 Hz), 122.73 (s), 127.21 (d,
J=23.6 Hz), 148.11 (d, J=6.4 Hz), 149.21 (s), 151.37 (s),
170.66 (s); 31P NMR (81 MHz, CDCl3), l 45.99 (s).
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Selected data for 4a: Rf=0.62 (EtOAc:MeOH, 9:1), 1H
NMR (250 MHz, CDCl3) l 1.10 (s, 9H), 1.37 (t, J=7.0
Hz, 3H), 1.98 (s, 3H), 2.93 (m, 2H), 3.51 (m, 2H), 3.61 (s,