Synthesis of [3-(3-chloro-4-fluorophenyl)-2-oxo-3,4-dihydro-2H- 2λ5-benzo[e][1,3,2]oxazaphosphinin-2-yl]-(aryl/alkyl) methanols and their bioactivity on sugarcane smut

Article abstract of DOI:10.1021/jf070850z

Synthesis of some new substituted [3-(3-chloro-4-fluorophenyl)-2-oxo-3,4- dihydro-2H-2λ⁵-benzo[e]-[1,3,2]oxazaphosphinin-2-yl]-(aryl/ alkyl)methanols (7a-k) based on the Pudovick reaction was accomplished in the presence of niobium pentoxide (Nb₂O₅) without using an external chiral ligand. Nb₂O₅ appears to form the metal complex intermediate catalyst system (6) by reacting with 3-(3-chloro-4-fluoro- phenyl)-3,4-dihydrobenzo[e][1,3,2]oxazaphosphinine-2-oxide (4), which not only directs the Pudovick addition reactions of aldehyde but also increases the yields and purity of the products. These compounds exhibited a lethal effect on whip smut of sugarcane and were degraded in the environment in the presence of bacteria and fungi to nontoxic phosphate residues that act as possible plant nutrients. Thus, a new class of benzooxazaphosphininyl methanol derivatives that act in synergy both as antipathogens and as plant nutrients in the environment have been discovered.

Full text of DOI:10.1021/jf070850z

J. Agric. Food Chem. 2007, 55, 6933−6939 6933
Synthesis of
[3-(3-Chloro-4-fluorophenyl)-2-oxo-3,4-dihydro-2H-2λ5
-
benzo[e][1,3,2]oxazaphosphinin-2-yl]-(aryl/alkyl) Methanols and
Their Bioactivity on Sugarcane Smut
Y. B. KIRAN,† P. VASU GOVARDHANA REDDY,† C. DEVENDRANATH REDDY,*,†
‡
D. GUNASEKAR,† AND N. P. ESWARA REDDY
Department of Chemistry, S.V. University, Tirupati-517 502, India, and Department of Plant
Pathology, Agricultural College, Tirupati-517 502, India
Synthesis of some new substituted [3-(3-chloro-4-fluorophenyl)-2-oxo-3,4-dihydro-2H-2λ5-benzo[e]-
[1,3,2]oxazaphosphinin-2-yl]-(aryl/alkyl)methanols (7a-k) based on the Pudovick reaction was
accomplished in the presence of niobium pentoxide (Nb2O5) without using an external chiral ligand.
Nb2O5 appears to form the metal complex intermediate catalyst system (6) by reacting with 3-(3-
chloro-4-fluoro-phenyl)-3,4-dihydrobenzo[e][1,3,2]oxazaphosphinine-2-oxide (4), which not only directs
the Pudovick addition reactions of aldehyde but also increases the yields and purity of the products.
These compounds exhibited a lethal effect on whip smut of sugarcane and were degraded in the
environment in the presence of bacteria and fungi to nontoxic phosphate residues that act as possible
plant nutrients. Thus, a new class of benzooxazaphosphininyl methanol derivatives that act in synergy
both as antipathogens and as plant nutrients in the environment have been discovered.
KEYWORDS: Pudovick reaction; benzooxazaphosphinyl methanols; niobium pentoxide; whip smut.
INTRODUCTION
nols (7a-k) and their epoxides (8a/b). Our endevour for the
preparation of the title compounds 7a-k and 8a/b was
accomplished by the Pudovik addition (5) of dialkyl/aryl
phosphates (4) with the carbonyl compounds (5) in the presence
of a triethylamine base and a Nb2O5 catalyst. The rationale for
their synthesis is that the oxazaphosphonate pharmacophore
present was expected to impart significant biological activity
since several organophosphorus compounds containing this
structural unit (Figure 1) have proven activity against bacteria,
viruses, fungi, cancer, and many other disease manifestations
(6-8). The presence of a 3-chloro-4-fluorophenyl group at the
nitrogen and R-hydroxyaryl/oxiranyl moiety at the phosphorus
of the phosphoryl pharmacophore structural unit (Figure 1)
embedded in the oxazaphosphinin ring system of the title
compounds (7a-k) may significantly reinforce bioactivity (9).
In addition, the R-hydroxy carbon provides the site for further
elaboration of these molecules that are useful as reagents in
organic synthesis and industry. The configuration at the R
carbon, being important for biological activity (10) and synthesis
of chiral, nonracemic R-hydroxy phosphoryl compounds, has
also gained serious attention.
Sugarcane is the most important commercial crop of India,
covering an area of about 3.6 million hectares with an annual
cane yield of about 237.1 million tonnes. The annual production
of raw sugar is about 10-11 million tons (1). The sugarcane
industry is in critical transition from an aggressive biosecurity
strategy to that of its economic industrial management (2). Over
100 fungi, 10 bacteria, 10 virus, and about 50 nematode species
are important sugarcane pests in different parts of the world.
Today, sugarcane agriculture all over the world is severely
damaged by whip smut (3). Sugarcane smut caused by the
fungus Ustilago scitaminea was first noted in South Africa in
1877. It is highly infectious and systemic and can spread even
by wind. It is a serious sugarcane disease which can reduce
yields by 30-100% (1-3). No chemical currently used as a
pesticide has been found to be effective against this disease once
it has infected the plants in the fields. Moreover, the applied
chemical pesticides are long-lived and cause toxic effects
through the food cycle in various life forms. In this context,
our continuous quest for the development of ecofriendly
antimicrobial and xenobiotics resulted in the synthesis of some
effective, short-lived, and biodegradable pesticides (4), 2-sub-
stituted [3-(3-chloro-4-fluoro-phenyl)-2-oxo-3,4-dihydro-2H-
2λ5-benzo[e][1,3,2]oxazaphosphinin-2yl]-(aryl/alkyl)metha-
MATERIALS AND METHODS
Experimental Chemistry. Solvents used were purified by the
established procedures (11). Progress of the reaction and purity of the
compounds were monitored by thin-layer chromatography (TLC) using
hexane-ethyl acetate (3:2) as an irrigating system and iodine as a
visualizing agent. Melting points were determined in open capillary
* Corresponding author. E-mail: profcdr@yahoo.co.in.
† S.V. University.
‡ Agricultural College.
10.1021/jf070850z CCC: $37.00
© 2007 American Chemical Society
Published on Web 07/28/2007

6934 J. Agric. Food Chem., Vol. 55, No. 17, 2007
Figure 1. Oxazaphosphoryl pharmacophore.
Kiran et al.
Caliphatic). 1H NMR (acetone-d6): δ 7.22-6.53 (m, 11H, Ar-H), 5.18-
5.08 (m, 2H, -CH2-), 4.55 (s, 1H, H-C-OH), 3.85 (brs, 1H, H-C-
OH). 13C NMR (acetone-d6): δ 43.68 (C-4), 130.18 (C-5), 123.48 (C-
6), 126.67 (C-7), 119.02 (C-8), 155.57 (C-9), 125.16 (C-10), 142.54
(C-1′), 118.37 (C-2′), 123.15 (C-3′), 155.34 (C-4′), 118.39 (C-5′),
114.78 (C-6′), 136.25(C-1′′), 131.20 (C-2′′ and C-6′′), 135.79 (C-3′′
and C-5′′), 125.18 (C-4′′), 63.13 (H-C-OH). 31P NMR (acetone-d6):
δ -4.20. Anal. Calcd for C20H15BrFClNO3P: C, 49.74; H, 3.13.
Found: C, 49.76; H, 3.19.
tubes on a Mel-temp apparatus and were uncorrected. Microanalyses
were performed on a Yanaca CHN Corder MT-3 elemental analyzer.
Infrared spectra (γmax in cm-1) were recorded as KBr pellets on a
JASCO FT/IR-5300. 1H and 13C NMR spectra were recorded on a
GEMINI 300 (300 and 75.46 MHz), and 31P NMR spectra were
recorded on a DRX 300 (121.5 MHz) using acetone (d6) and DMSO-
(d6) (DMSO ) dimethylsulfoxide). The 1H and 13C chemical shifts were
referenced to tetramethylsilane and 85% H3PO4 for 31P chemical shifts.
Mass spectra were recorded on a Jeol SX 102 DA/600 mass spectrom-
eter using argon/xenon (6 kV, 10 mA) as the fast atom bombardment
(FAB) gas.
[3-(3-Chloro-4-fluorophenyl)-2-oxo-3,4-dihydro-2H-2λ5-benzo[e]-
[1,3,2]oxazaphosphinin-2-yl]-4-hydroxyphenylmethanol (7d). mp: 97-
99 °C. IR (KBr): 3254 (-OHaliphatic), 1223 (PdO), 756 cm-1 (P-
C
aliphatic). 1H NMR (acetone-d6): δ 7.82-6.61 (m, 11H, Ar-H), 5.12-
4.98 (m, 2H, -CH2-), 4.63 (s, 1H, H-C-OH), 3.67 (brs, 1H, H-C-
OH), 9.83 (s, 1H, 4′′-OH). 13C NMR (acetone-d6):δ 43.80 (C-4),
129.28 (C-5), 120.34 (C-6), 128.47 (C-7), 115.91 (C-8), 156.24 (C-9),
125.77 (C-10), 143.42 (C-1′), 117.54 (C-2′), 120.32 (C-3′), 152.54(C-
4′), 117.26 (C-5′), 114.72 (C-6′), 129.80 (C-1′′), 130.23 (C-2′′ and
Synthesis.
3-(3-Chloro-4-fluorophenyl)-3,4-dihydrobenzo[e]-
[1,3,2]oxazaphosphinine-2-oxide (4). A solution of PBr3 (0.93 mL, 2.7
g, 0.01 mol) in dry toluene (10 mL) was added dropwise over a period
of 15 min to a stirred solution of R-(3-chloro-4-fluoroaniline)-2-cresol
(1) (2.51 g, 0.01 mol) (8) and triethylamine (2.78 mL, 2.02 g, 0.02
mol) in dry toluene (30 mL) at 0 °C. After addition, stirring was
continued for 3 h at 50 °C. Triethylamine hydrobromide was filtered
off. To the filtrate containing 2-bromo-3-(3-chloro-4-fluorophenyl)-3,4-
dihydro-2H-benzo[e][1,3,2]oxazaphosphinine (2) was added triethy-
lamine (1.34 mL, 1.01 g, 0.01 mol), and the solution was stirred at
0 °C. Water (0.018 g, 0.01 mol) was added through a septum, using a
Hamilton 50 µL syringe, to the vessel cooled in an ice-salt bath at
0 °C with stirring for an additional 2 h at 25 °C to obtain 3 and 4. The
solution was dried over anhydrous Na2SO4 for 2 h, decanted, and used
for further reaction (Scheme 1).
Synthesis of 7a-k. [3-(3-Chloro-4-fluorophenyl)-2-oxo-3,4-dihydro-
2H-2λ5-benzo[e][1,3,2]oxazaphosphinin-2-yl]phenylmethanol (7a). The
mixture of 3 and 4 (0.01 mol), alkyl/aryl aldehyde (5) (0.01 mol), Et3N
(0.05 mol), and a catalytic quantity of Nb2O5 in toluene (20 mL) was
stirred for 4 h at 50 °C. (Table 1). After completion of the reaction as
indicated by TLC, the reaction mixture was filtered, and the filtrate
was adsorbed on silica gel G (60-120 mesh). Compound 7a was
obtained in the pure state by column chromatography using a 2-ft-
length and 0.5-ft-diameter glass column and 3:1 ethyl acetate/hexane
as the eluent (Scheme 1).
mp: 116-118 °C. IR (KBr): 3260 (-OHaliphatic), 1218 (PdO), 756
cm-1 (P-Caliphatic). 1H NMR (DMSO-d6): δ 7.18-6.50 (m, 12H, Ar-
H), 5.11-5.07 (m, 2H, -CH2-), 4.55 (s, 1H, H-C-OH), 3.57 (brs,
1H, H-C-OH). 13C NMR (DMSO-d6): δ 41.48 (C-4), 128.35 (C-5),
122.32 (C-6), 127.74 (C-7), 116.68 (C-8), 155.10 (C-9), 125.01(C-
10), 146.42 (C-1′), 116.96 (C-2′), 121.82 (C-3′), 150.47 (C-4′), 118.84
(C-5′), 114.97 (C-6′), 137.23 (C-1′′), 129.63 (C-2′′ & C-6′′), 129.01
(C-3′′ & C-5′′), 132.20 (C-4′′), 70.80 (H-C-OH). 31P NMR (DMSO-
d6): δ -11.02. FAB MS: m/z (%) 405 (5) [M+•+2], 403 (13) [M+•],
401 (3), 327 (5), 281 (11), 251 (9), 246 (7), 147 (38), 123 (16), 107
(19), 73 (100). Anal. Calcd for C20H16FClNO3P: C, 59.49; H, 3.99.
Found: C, 59.56; H, 4.01.
C-6′′), 115.86 (C-3′′ and C-5′′), 159.34 (C-4′′), 70.25 (H-C-OH). 31
P
NMR (acetone-d6): δ -7.48. Anal. Calcd for C20H16FClNO4P: C,
57.19; H, 3.83. Found: C, 57.25; H, 3.88.
[3-(3-Chloro-4-fluorophenyl)-2-oxo-3,4-dihydro-2H-2λ5-benzo[e]-
[1,3,2]oxazaphosphinin-2-yl]-2-hydroxyphenylmethanol(7e).mp: 240(d)°C.
IR (KBr): 3260 (-OHaliphatic), 1221 (PdO), 756 cm-1 (P-Caliphatic).
1H NMR (acetone-d6): δ 7.17-6.50 (m, 11H, Ar-H), 5.03-4.85 (m,
2H, -CH2-), 4.54 (s, 1H, H-C-OH), 3.51(brs, 1H, H-C-OH), 9.57
(s, 1H, 2′′-OH).13C NMR (DMSO-d6): δ 41.67 (C-4), 128.37 (C-5),
118.88 (C-6), 127.77 (C-7), 115.70 (C-8), 157.23 (C-9), 124.66 (C-
10), 144.57 (C-1′), 116.98 (C-2′), 118.88 (C-3′), 154.77 (C-4′), 116.70
(C-5′), 114.91 (C-6′), 124.22 (C-1′′), 153.12 (C-2′′), 119.74 (C-3′′),
136.41 (C-4′′), 121.39 (C-5′′), 128.37 (C-6′′), 71.92 (H-C-OH). 31P
NMR (acetone-d6): δ -7.57. Anal. Calcd for C20H16FClNO4P: C,
57.19; H, 3.83. Found: C, 57.23; H, 3.79.
[3-(3-Chloro-4-fluorophenyl)-2-oxo-3,4-dihydro-2H-2λ5-benzo[e]-
[1,3,2]oxazaphosphinin-2-yl]-2-hydroxy-4-chlorophenylmethanol (7f).
mp: 78-80 °C. IR (KBr): 3258 (-OHaliphatic), 1224 (PdO), 756 cm-1
1
(P-Caliphatic). H NMR (acetone-d6): δ 7.27-6.61 (m, 10H, Ar-H),
5.01-4.89 (m, 2H, -CH2-), 4.63 (s, 1H, H-C-OH), 3.08 (brs, 1H,
H-C-OH), 8.66 (s, 1H, 2′′-OH). 13C NMR (acetone-d6): δ 43.15
(C-4), 128.30 (C-5), 119.75 (C-6), 126.58 (C-7), 116.74 (C-8), 156.94
(C-9), 124.37 (C-10), 140.57 (C-1′), 117.98 (C-2′), 111.76 (C-3′),
154.21 (C-4′), 117.27 (C-5′), 113.82 (C-6′), 122.49 (C-1′′), 158.52 (C-
2′′), 116.76 (C-3′′), 142.80 (C-4′′), 120.85 (C-5′′), 133.28 (C-6′′), 61.02
(H-C-OH). 31P NMR (acetone-d6): δ -7.92. Anal. Calcd for C20H15-
FCl2NO4P: C, 52.85; H, 3.32. Found: C, 52.79; H, 3.39.
[3-(3-Chloro-4-fluorophenyl)-2-oxo-3,4-dihydro-2H-2λ5-benzo[e]-
[1,3,2]oxazaphosphinin-2-yl]-3-hydroxy-4-methoxyphenylmethanol (7g).
mp:130-131 °C. IR (KBr): 3256 (-OHaliphatic), 1222 (PdO), 756 cm-1
1
(P-Caliphatic). H NMR (acetone-d6): δ 7.46-6.57 (m, 10H, Ar-H),
5.13-5.04 (m, 2H, -CH2-), 4.80 (s, 1H, H-C-OH), 3.80 (brs, 1H,
H-C-OH), 9.81 (s, 1H, 3′′-OH), 3.91 (s, 3H, -OCH3). 13C NMR
(acetone-d6): δ 43.69 (C-4), 128.84 (C-5), 120.28 (C-6), 127.02 (C-
7), 115.75 (C-8), 156.00 (C-9), 124.77 (C-10), 143.57 (C-1′), 117.56
(C-2′), 119.26 (C-3′), 154.27 (C-4′), 117.27 (C-5′), 114.12 (C-6′),
129.43 (C-1′′), 120.29 (C-2′′), 142.79 (C-3′′), 156.80 (C-4′′), 115.75
(C-5′′), 134.28 (C-6′′), 67.47 (H-C-OH), 55.03 (-OCH3). 31P NMR
(acetone-d6): δ -8.83. FAB MS: m/z (%) 451 (4) [M+•+2], 449 (13)
[M+•], 327 (38), 281 (29), 251 (26), 228 (47), 147 (100), 73 (38). Anal.
Calcd for C21H18FClNO5P: C, 56.05; H, 4.03. Found: C, 56.08; H,
4.02.
Compounds 7b-k were prepared by the above procedure using
respective aldehydes.
[3-(3-Chloro-4-fluorophenyl)-2-oxo-3,4-dihydro-2H-2λ5-benzo[e]-
[1,3,2]oxazaphosphinin-2-yl]-4-chlorophenylmethanol(7b).mp: 230(d)°C.
IR (KBr): 3362 (-OHaliphatic), 1222 (PdO), 765 cm-1 (P-Caliphatic).
1H NMR (acetone-d6): δ 7.12-6.73 (m, 11H, Ar-H), 5.10-4.92 (m,
2H, -CH2-), 3.93 (s, 1H, H-C-OH), 3.53 (brs, 1H, H-C-OH).
13C NMR (acetone-d6): δ 42.71(C-4), 127.89 (C-5), 122.42 (C-6),
126.68 (C-7), 118.94 (C-8), 156.78 (C-9), 125.11(C-10), 144.57 (C-
1′), 118.87 (C-2′), 122.18 (C-3′), 153.77 (C-4′), 118.07 (C-5′), 112.91
(C-6′), 135.25(C-1′′), 131.20 (C-2′′ and C-6′′), 129.79 (C-3′′ and C-5′′),
142.89 (C-4′′), 61.83 (H-C-OH). 31P NMR (acetone-d6): δ -10.85.
FAB MS: m/z (%) 441 (3) [M+•+4], 439 (12) [M+•+2], 437 (18) [M+•],
326 (18), 280 (44), 251 (37), 145 (100), 107 (21). Anal. Calcd for
C20H15FCl2NO3P: C, 54.78; H, 3.44. Found: C, 54.72; H, 3.47.
[3-(3-Chloro-4-fluorophenyl)-2-oxo-3,4-dihydro-2H-2λ5-benzo[e]-
[1,3,2]oxazaphosphinin-2-yl]-4-bromophenylmethanol (7c). mp: 178-
180 °C. IR (KBr): 3385 (-OHaliphatic), 1224 (PdO), 768 cm-1 (P-
[3-(3-Chloro-4-fluorophenyl)-2-oxo-3,4-dihydro-2H-2λ5-benzo[e]-
[1,3,2]oxazaphosphinin-2-yl]-3-nitrophenylmethanol (7h). mp:150-
152 °C. IR (KBr): 3269 (-OHaliphatic), 1222 (PdO), 729 cm-1
1
(P-Caliphatic). H NMR (acetone-d6): δ 8.72-7.91 (m, 11H, Ar-H),
5.16-4.92 (m, 2H, -CH2-), 4.63 (s, 1H, H-C-OH), 2.94 (brs, 1H,
H-C-OH). 13C NMR (acetone-d6): δ 43.77(C-4), 129.16 (C-5), 120.32
(C-6), 128.89 (C-7), 115.91 (C-8), 157.23 (C-9), 124.61 (C-10), 142.82
(C-1′), 117.56 (C-2′), 120.34 (C-3′), 154.93 (C-4′), 117.34 (C-5′),
114.15 (C-6′), 138.64 (C-1′′), 124.61 (C-2′′), 150.12 (C-3′′), 129.16
(C-4′′), 127.55 (C-5′′), 135.29 (C-6′′), 87.90 (H-C-OH). 31P NMR
(acetone-d6): δ -9.22. FAB MS: m/z (%) 450 (5) [M+•+2], 448 (16)

Synthesis of Methanols and Their Bioactivity
J. Agric. Food Chem., Vol. 55, No. 17, 2007 6935
Scheme 1 . Synthetic Scheme for Benzoxazaphosphinin-2-yl-(aryl/alkyl) Methanols 7a
−k
Table 1. Effect of Nb2O5 on the Reaction Time and Yield of Compounds 7a−k
S.No of compd.
time period in hours
7a
7b
7c
7d
7e
7f
7g
7h
7i
7j
17
42
10.30
97
7k
2.5
65
2
92
3.5
3
53
2
2
2
2.30
57
2
76
2
3.15
2
57
1
20
27
15
88
with out Nb2O5
yields %
time period in hours
yields %
55
2.15
73
56
1.30
93
51
1.75
85
59
1.15
83
61
2.5
81
with Nb2O5
75
71
[M+•], 326 (33), 293 (3), 280 (46), 251 (59), 233 (24), 145 (100). Anal.
Calcd for C20H15FClN2O5P: C, 53.52; H, 3.36. Found: C, 53.57; H,
3.37.
[3-(3-Chloro-4-fluorophenyl)-2-oxo-3,4-dihydro-2H-2λ5-benzo[e]-
[1,3,2]oxazaphosphinin-2-yl]-but-2-en-1-ol (7k). mp: 142-144 °C. IR
1
(KBr): 3447 (-OHaliphatic), 1225 (PdO), 757 cm-1 (P-Caliphatic). H
[3-(3-Chloro-4-fluorophenyl)-2-oxo-3,4-dihydro-2H-2λ5-benzo[e]-
[1,3,2]oxazaphosphinin-2-yl]thiophenemethanol (7i). mp: 118-119 °C.
IR (KBr): 3258 (-OHaliphatic), 1201 (PdO), 756 cm-1 (P-Caliphatic).
1H NMR (acetone-d6): δ 7.25-6.60 (m, 10H, Ar-H), 5.21-5.09 (m,
2H, -CH2-), 4.62 (s, 1H, H-C-OH), 3.22 (brs, 1H, H-C-OH).
13C NMR (CDCl3): δ 43.68 (C-4), 129.47 (C-5), 120.71 (C-6), 128.83
(C-7), 115.85 (C-8), 155.98 (C-9), 124.56 (C-10), 143.57 (C-1′), 117.56
(C-2′), 120.71 (C-3′), 158.00 (C-4′), 117.27 (C-5′), 114.20 (C-6′),
139.16 (C-1′′), 133.36 (C-2′′), 130.36 (C-3′′), 131.54 (C-4′′), 61.84 (H-
C-OH). 31P NMR (acetone-d6): δ -9.43. FAB MS: m/z (%) 411(7)
[M+•+ 2], 409(18) [M+•], 327 (4), 281 (8), 251 (11), 207 (12), 193
(5), 147 (33), 73 (100). Anal. Calcd for C18H14FClNO3PS: C, 52.82;
H, 3.44. Found: C, 52.87; H, 3.47.
NMR (acetone-d6): δ 7.26-6.61 (m, 7H, Ar-H), 5.15-4.97 (m, 2H,
-CH2-), 4.63 (s, 1H, H-C-OH), 3.06 (brs, 1H, H-C-OH), 5.20-
4.85 (m, 2H, -aCHdbCH-), 1.28 (s, 3H, -cCH3). 13C NMR (acetone-
d6): δ 43.68 (C-4), 129.49 (C-5), 120.29 (C-6), 128.82 (C-7), 117.56
(C-8), 157.23 (C-9), 128.55 (C-10), 141.57 (C-1′), 117.27 (C-2′), 120.29
(C-3′), 155.49 (C-4′), 115.94 (C-5′), 114.13 (C-6′), 118.12 (aC), 134.92
(bC), 21.32 (cC), 61.93 (H-C-OH). 31P NMR (acetone-d6): δ -7.64.
Anal. Calcd for C17H16FClNO3P: C, 55.36; H, 4.61. Found: C, 55.31;
H, 4.57.
Synthesis of 8a/b. Compound 7j/k (0.01 mol) was dissolved in
dichloromethane (30 mL). Hydrogen peroxide (30% H2O2, 0.01 mol)
containing three drops of hexachloro acetone as a catalyst was added
to it dropwise at 0-5 °C (12). The mixture was brought to room
temperature and kept for 2 h. On completion of the reaction, as
ascertained by TLC analysis, the compounds 8a and 8b were obtained
in the pure state by column chromatography (Scheme 2).
[3-(3-Chloro-4-fluorophenyl)-2-oxo-3,4-dihydro-2H-2λ5-benzo[e]-
[1,3,2]oxazaphosphinin-2-yl]-3-phenyl-2-propen-1-ol (7j). mp: 101-
103 °C. IR (KBr): 3298 (-OHaliphatic), 1222 (PdO), 756 cm-1 (P-
C
aliphatic). 1H NMR (acetone-d6): δ 7.12-6.76 (m, 12H, Ar-H), 5.17-
[3-(3-Chloro-4-fluorophenyl)-2-oxo-3,4-dihydro-2H-2λ5-benzo[e]-
[1,3,2]oxazaphosphinin-2-yl]-3-phenyloxiranylmethanol (8a). mp: 250-
252 °C. IR (KBr): 3276 (-OHaliphatic), 1262 (PdO), 750 cm-1
5.02 (m, 2H, -CH2-), 4.80 (s, 1H, H-C-OH), 3.22 (brs, 1H, H-C-
OH), 6.69-6.60 (m, 2H, -aCHdbCH-). 13C NMR: Solubility was
too low for recording. 31P NMR (acetone-d6): δ -8.79. Anal. Calcd
for C22H18FClNO3P: C, 61.47; H, 4.22. Found: C, 61.53; H, 4.19.
1
(P-Caliphatic). H NMR (acetone-d6): δ 7.65-6.42 (m, 12H, Ar-H),
5.21-4.99 (m, 2H, -CH2-), 4.52 (s, 1H, H-C-OH), 3.09 (brs, 1H,

6936 J. Agric. Food Chem., Vol. 55, No. 17, 2007
Kiran et al.
Scheme 2 . Synthetic Scheme for Benzoxazaphosphinin-2-yl-(aryl/alkyl) oxiranylmethanol 8a/b
Table 2. Sensitivity of Spores of Smut of Saccharum officinarum to 7a−
k and 8a/b in Slide Germination Techniquea
1000 ppm
T
750 ppm
T
500 ppm
T
250 ppm
T
100 ppm
test compound
C
P
C
P
C
P
C
P
C
T
P
7a
7b
7c
7d
7e
7f
7g
7h
7i
7j
7k
100
100
100
100
100
100
100
100
100
100
100
100
100
100
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
18
11
13
18
17
07
05
03
08
13
10
11
08
09
82
89
87
82
83
93
95
97
92
87
90
89
92
91
100
100
100
100
100
100
100
100
100
100
100
100
100
100
44
36
32
38
42
23
19
12
27
34
37
34
39
23
56
64
68
62
58
77
81
88
73
66
63
66
61
77
8a
8b
bavistin
a C
)
number of spores germinated in the control; T
)
number of spores germinated in treatment; P
)
percentage inhibition over control [C
−
T/C
× 100].
H-C-OH), 5.36-5.16 (m, 2H, -epoxide-). 13C NMR: Solubility
was too low for recording. 31P NMR (acetone-d6): δ -4.33. FAB MS:
m/z (%) 467 (7) [M+•+2], 465 (12) [M+•] , 463 (14), 369 (26), 327
(15), 281 (27), 252 (30), 212 (12), 124 (100). Anal. Calcd for C22H18-
FClNO4P: C, 53.25; H, 4.42. Found: C, 53.32; H, 4.51.
Table 3. Percent of Inhibition by 7a
−k and 8a/b on Smutted Shoot
test
compound
1000
ppm
750
ppm
500
ppm
250
100
ppm
ppm
A
B
7a
7b
7c
7d
7e
7f
7g
7h
7i
7j
7k
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
97
98
92
94
96
98
97
100
100
100
100
100
100
100
100
70
83
85
88
87
87
98
97
92
94
85
91
87
95
65
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
[3-(3-Chloro-4-fluorophenyl)-2-oxo-3,4-dihydro-2H-2λ5-benzo[e]-
[1,3,2]oxazaphosphinin-2-yl]-3-methyloxiranylmethanol (8b). mp: 237-
239 °C. IR (KBr): 3260 (-OHaliphatic), 1222 (PdO), 756 cm-1 (P-C
100
100
100
100
100
100
100
100
100
100
100
100
1
aliphatic). H NMR (acetone-d6): δ 7.26-6.61 (m, 7H, Ar-H), 5.13-
5.01 (m, 2H, -CH2-), 4.63(s, 1H, H-C-OH), 3.18 (brs, 1H, H-C-
OH), 4.63-4.38 (m, 2H, -epoxide-), 2.14-2.03 (m, 3H, CH3). 13C
NMR: Solubility was too low for recording. 31P NMR (acetone-d6):
δ -5.98. Anal. Calcd for C17H16FClNO4P: C, 58.51; H, 3.61. Found:
C, 58.62; H, 3.78.
Bioassays. Compounds 7a-k and 8a/b were tested for their
bioactivity on whip smut of the sugarcane plant (Saccharum offici-
narum) and biodegradation in the environment and in the soil.
Effect on Smut of Sugarcane. Slide Germination Technique. A spore
suspension was prepared from 10-day-old cultures of whip smut
(Ustilago scitaminea). The spores were harvested with the help of a
camel’s hair brush by scraping over the culture and suspending the 10
mL of sterile distilled water in a test tube. The spore density was
adjusted with distilled water so as to get 5.0 × 104 spores/mL with the
help of a hemeocytometer (13).
Stock solutions of test compounds (7a-k and 8a/b) and reference
compound (bavistin) were prepared by dissolving required quantities
in ethanol and diluting with 100 mL of sterile distilled water. Later
test concentrations as given in the Tables 2 and 3 were prepared by
the serial dilution method.
The test and reference compounds containing 0.25 mL of test and
reference solution, respectively, were placed in one of the two cavities
of a microscopic cavity slide with the other cavity as a control. The
solvent was allowed to evaporate, leaving a deposit of the test compound
in the cavity of the slide. Equal quantities of the spore suspension were
placed in cavities over the dried test compound. The cavities were
covered with cover slips, and the slides were incubated in a moist
chamber at 25 ( 2 °C for 24 h. The experiment was replicated three
times, and control was maintained with distilled water in place of the
test compound solution (Table 2).
8a
8b
bavistin
Effect of the Test Compound Treated on the Disease-Induced Plants.
Exactly 15 pots were filled with sterile soil, and to each pot, a
disinfected sugarcane stem piece, treated with formalin, was transferred
and covered with a layer of soil in a greenhouse. For each treatment,
15 plants were treated. The pots were regularly watered to produce
plants. Except for control “A” and control “B”, all of the remaining 13
plants were treated with a test compound by foliar application at a
specific quantity at recommended concentrations in an aqueous ethanol
and water suspension. Later, after 2 days, control “B” and all the
remaining treatments were sprayed with a smut spore suspension of
Ustilago scitaminea to infect axillary buds through sporidia. The plants
were observed for disease symptoms (14) from the 15th day to 60th
day (Table 3).
Application on the Infected Plants. A total of 15 infected sugarcane
plants that were 45 days old were selected in a farm enclosure for each
treatment. Except for controls “A” and “B”, all remaining 13 plants
infected with Ustilago scitaminea were treated with a test compound
by foliar application at a specific quantity at recommended concentra-
tions (1000 ppm) in an aqueous ethanol and water suspension. For each

Synthesis of Methanols and Their Bioactivity
J. Agric. Food Chem., Vol. 55, No. 17, 2007 6937
Table 4. Effect of 7a k and 8a/b on the Number of Colonies of Phosphate Solubilizing Bacteria
−
T
7a
7b
7c
7d
7e
7f
7g
7h
7i
7j
7k
8a
8b
control
C
21.6
23.2
21.7
20.4
22.7
23.8
24.7
20.2
24.7
23.2
22.4
23
22.5
T
) test compound; C ) total number of colonies of phosphate solubilizing bacteria.
Table 5. Number of Colony-Forming Units of Bacteria and Fungi by 7a−k and 8a/b
T
7a
7b
7c
7d
7e
7f
7g
7h
7i
7j
7k
8a
8b
calvixin
B
F
4060
420
4962
540
3645
285
3980
320
4140
448
5180
394
4780
298
6460
580
3280
414
3005
245
4890
420
5240
386
3870
210
2840
142
T
)
test compound; B
)
bacteria; F
)
fungi.
treatment, 15 plants were selected. Later, the plants were observed
periodically for disease incidence (14) from the 4th day to 30th day.
Testing of Spore Germination. After the eighth day of treatment with
test compounds, the spores of Ustilago scitaminea were collected from
all of the above treated plants. The spore shapes were observed under
the microscope, and their germination was artificially carried out by
the method of Horsfall and Rich (7) with certain modifications. The
treated and untreated spores were placed in two cavities of a microscopic
cavity slide. The spore suspension prepared with sterile distilled water
was adjusted to give 25-30 conidia of test organisms per 100 µL of
spore suspension. Then, 100 µL of spore suspension was transferred
on to each cavity of the microscopic slide. The cavities were covered
with coverslips, and the slides were incubated in a moist chamber at
25 ( 2 °C for 24 h.
Phosphorus Transformation. (a) Colorimetric Method. Three test
tubes, each containing 5 mL of distilled water, were taken and labeled
as 1, 2, and 3. To test tubes 1 and 2 was added 1 mg of the test
compound. To test tubes 1 and 3 was added an inoculums of phosphate
solubilizing bacteria. After 7 days, the contents found in the three test
tubes were filtered through bacterial filters and collected separately.
The amount of soluble inorganic phosphates was measured by the
colorimetric method (15) (Table 4). All the test compounds were
screened in the same way.
(b) Dilution Plate Method. Soil samples from the sugarcane field
were collected for the isolation of pesticide degrading/utilizing bacteria
and fungi using the dilution plate method (16). The test compounds
7a-k and 8a/b were used to study the effect on the microbial
population. Calixin, supplied by BASF-AG, Germany, was used as a
reference compound. Soil extract agar and Czapek-Dox agar (17)
amended with 100 ppm test compounds and Calixin were used for the
enumeration of bacteria and fungi, respectively. Calixin-treated plates
were considered as the control. The soil extract agar plates were
incubated at 37 °C for bacterial growth, while the Czapek-Dox agar
plates were incubated in an inverted position at room temperature
(26 ( 2 °C) for fungal growth. The plates were observed regularly for
the development of microbial colonies. On the basis of the colony
morphology and microscopic observation, the bacterial and fungal
species were identified, and the number of colony-forming units per
gram of soil were calculated (Table 5).
phosphoryl OdP(V)-H system (19). The hydrolysis should be
done in the presence of triethylamine by the addition of a
calculated quantity of water only. The addition of a little excess
water led to an acid-catalyzed hydrolysis, giving the starting
compound (1). The ease of addition of 4 to 5 and the percent
yield of the products (7a-k) appeared to depend on the nature
of the aldehyde. The addition of 4 to the arylaldehydes was
completed in a short period of time, giving high yields of 7a-k
when compared to that of aliphatic aldehydes, which required
more time (15-20 h) and gave poor yields. This could be due
to the higher stability of the proposed intermediate 6 where
greater delocalization of the electron density over the neighbor-
ing phosphoryl and aryl groups takes place. Furthermore, the
overall reaction rate, the purity, and yield of the title compounds
7a-k increased in the presence of a catalytic amount of Nb2O5
(Table 1). The mechanism and the role played by Nb2O5 is not
known. Perhaps it may initially form an intermediate complex
6, by reacting with 4 and activating the generation of the
oxazaphosphinin-2-oxide anion 6 by catalyzing the selective
partial deprotonation (20) of 4. This consequently facilitates the
formation of a P-C bond between the P of oxazaphosphinine
(4) and the C of aldehyde 5. The incorporation of Nb2O5 and
Et3N into the one face of the phosphorus nucleophile 6 enables
it to discriminate the enantiotopic faces of the carbonyl carbon
of the aldehyde and diastereoselectively add to it. Thus, the
formation of only a single racemic compound of 7a-k is
favored. The presence of a single spot in TLC and one 31P NMR
chemical shift for 7a-k confirmed this conclusion (21). Nb2O5
seems to have great potential as a chiral catalytic template that
could mediate the stereochemistry of this addition. The syn-
thesized compounds are characterized by elemental analysis;
1
IR; H, 13C, and 31P NMR; and mass spectral data (22, 23).
7a-k and 8a/b showed IR absorption bands in the regions
1262-1201, 768-729, and 3447-3069 cm-1 for PdO,
P-C(aliphatic), and (C)-O-H(aliphatic), respectively (24). The
aromatic protons of 7a-k and 8a/b resonated as multiplets
slightly downfield (δ 8.72-6.49) when compared with those
of the starting compound 1 (δ 7.20-7.49) owing to the
deshielding effect of the benzoxazaphosphinin-2-oxide system.
(7, 8) The C-4 methylene protons exhibited a multiplet,
indicating their non-equivalence and coupling with phosphorus
in the six-membered ring (8). The aliphatic proton and the
hydroxyl proton of H-C-OH gave signals in the regions δ
4.80-3.93 and δ 3.85-2.94, respectively (18). The 13C NMR
chemical shifts for C-4 to C-10, C-1 to C-6, and C-1′′ to C-6′′
were observed in the expected regions. The carbon signal of
the aliphatic alcohol moiety appeared at δ 87.90-51.72 (18,
22). The mass spectra of the representative compounds 7a, 7b,
RESULTS AND DISCUSSION
Synthesis. The addition of an equimolar amount of PBr3 to
1 in dry toluene to obtain 2 depends on the temperature. If the
reaction was carried out at room temperature, even after 8 h,
some starting compound 1 remained in the reaction. At 50 °C,
the reaction was completed in 3 h without leaving 1. The
preparation of 2 was carried out in the presence of a dry, inert
atmosphere to prevent the early hydrolysis of the phosphorus
bromides. It was observed that the hydrolysis of a P-Br bond
was completed in a short time when compared to that of a P-Cl
bond (18). The hydrolysis of a P-Br bond of 2 afforded P(III)-
OH of 3, which instantaneously rearranged into a more stable

6938 J. Agric. Food Chem., Vol. 55, No. 17, 2007
Kiran et al.
7g, 7h, 7i, and 8a were in accord with those reported for such
types of organophosphorus compounds (7, 8). They exhibited
chlorine isotopic peaks at (M+2)+. The M+ peaks with the
expected m/z value in the required ratio. The presence of
characteristic ions with the benzoxazaphosphinin ring along with
substituents at m/z 403, 327, 281, and 246 was in good
agreement with the proposed structures.
riendly since they were degraded in the presence of some soil
microbes to nontoxic phosphate residues.
ACKNOWLEDGMENT
The authors express their thanks to Dr. C. Naga Raju, Assistant
Professor, Dept of Chemistry, S. V. University, Tirupati, India,
for his helpful suggestions and to The Director, CDRI, Lucknow,
India, for the analytical data.
Biological Activity. Effect on Spore Germination. The effect
of the title compounds was initially tested in vitro by the slide
germination test (13). After 24 h of incubation, a spore
germination count was taken by using a compound microscope.
The inhibition efficiencies of the test compounds were compared
with inhibition efficiencies of the reference compound bavistin
(carbendenzim). The results are shown in Table 2.
Supporting Information Available: A detailed Scheme 1
1
giving full structures is given. The IR, 31P, H, 13C, and FAB
mass spectra of 7a and its mass fragmentation are given as
representative examples of this series. In addition, the 31P
spectrum of 7j is also given. The color photographs of the effect
of the test compounds 7f, 7g, 7h, and 7i on the smut of sugar
cane and the healthy growth of the side tillers in the infected
plants after the treatment are also given. The standard error of
the mean for the assay values is also available. This material is
available free of charge via the Internet at http://pubs.acs.org.
Drying of Whip Region. The encouraging results of the test
compounds on the diseases infected plants induced us to carry
out field-level studies (Table 3).
The plants treated with test compounds were found to be dried
with splitting of the whip region when compared to those of
the control. This type of effect was strongly observed in plants
treated with test compounds 7f, 7g, 7h, and 7i. However, similar
effects were not observed in the plants treated with bavistin
supplied by BASF-India Ltd.
LITERATURE CITED
(1) Ajit, N. Pulse of Indian Sugar Industry. Sugar India - Year
Book’-06; Sakal papers Ltd: Kolapur, India, 2006; p 105.
(2) Gururaj, H. Sugarcane in Agriculture and Industry; Prism Books
Pvt. Ltd.: India, 2001; pp 1-472.
(3) Rangaswami, G. Duiseases of cash crops. Diseases of Crop
Plants in India, 3rd ed.; Prentice Hall of India Pvt. Ltd.: New
Delhi, India, 1996; pp 380-384.
(4) Kumar, S.; Mukerji, K. G.; Lal, R. Molecular aspects of pesticide
degradation by microorganisms. Crit. ReV. Microbiol. 1996, 22
(1), 1-26
(5) Pudovik, A. N.; Konovalova, I. V. Addition reactions of esters
of phosphorus(III) acids with unsaturated systems. Synthesis
1979, 2, 81-96.
These results further revealed that these compounds not only
cause the complete death and drying of the whip region of
sugarcane plants but also promote the growth of the plants,
simultaneously producing healthy side tillers in the clump
without further infection. This indicated that the systemic
spreading of the disease has been completely arrested in the
plants treated with test compounds. Further, the test compounds
prevented the secondary spread of the disease in the field to
other healthy plants. These results are very encouraging when
compared to the effect of Bavistin.
(6) Srinivasulu, D.; Devendranath Reddy, C.; Suresh Reddy, C.;
Brown, C.W.; Hager, J. D.; Means, M. D.; Berlin, K. D.
Synthesis and anti-microbial activity of 2-substituted-2,3-dihydro-
3-(4′-bromophenyl)-1H-naphth[1,2-e][1,3,2]-oxaza- phosphorin-
2-oxides/sulfides. Phosphorus, Sulfur Silicon Relat. Elem. 2000,
167, 181-193.
(7) Kiran, Y. B.; Kasthuraiah, M.; Naga Raju, C.; Gunasekar, D.;
Madhu Babu, S. V. S.; Devendranath Reddy, C. Synthesis and
bioactivity of some new 2-substituted-3,4-dihydro-3-(3′-chloro-
4′-fluorophenyl)-2H-1,3,2-benzoxazaphos-phorin-2-oxides. In-
dian J. Chem. 2005, 44B, 2171-2177.
(8) Kiran, Y. B.; Gunasekar, D.; Devendranath Reddy, C.; Suresh
Reddy, C.; Tran, K.; Le, T.; Berlin, K. D.; Srinivasan, S.;
Charitha Devi, M. Synthesis and bioactivity of some new
N-(substituted aryl/alkyl/cyclohexyl)-N′-[2,3-dihydro-2-oxido-
3-(3′chloro-4′-fluorophenyl)-1H-(1,3,2)oxazaphosphorin-2-yl]-
ureas. Pest Manage. Sci. 2005, 61, 1016-1023.
(9) Quin, L.D. A Guide To Organophosphorus Chemistry; John
Wiley and Sons, Inc.: New York, 2000; Chapter 11, pp 351-
383.
(10) Rath, N. P.; Spilling, C. D. The enantio selective addition of
dialkylphosphites to aldehydes. Catalysis by a lanthanum bi-
naphthoxide complex. Tetrahedron Lett.1994, 35 (2), 227-230.
(11) Brain, S. F.; Antony, J. H.; Peter, W. G. S.; Austin, R. T.
Experimental techniques. Vogel’s Text Book of Practical Organic
Chemistry, 5th ed.; Addison Wesley Longman Ltd.: England,
1989; pp 165-186.
(12) Kasthuraiah, M. Synthesis, Spectral Characteristics and Bioac-
tiVity of Some Organophosphorus Heterocyclic Compounds;
Sri Venkateswara University: Tirupati, India, 2004; pp 131-
134.
Spores Become Inactive. It was found that no single spore
was germinated, when treated at 1000-250 ppm; moreover, the
spores collected from plants treated with 100 ppm show a slight
germination, but the germination was also found to be not
healthy.
Interaction between Microorganisms and Test Com-
pounds. The solution from test tube 1 was found to contain
20-25 µg of soluble inorganic phosphate, whereas tubes 2 and
3 were found to contain negligible or only traces of inorganic
phosphates (Table 4). This shows that the molecules are easily
degradable by microbial action to phosphate residues, which in
turn may possibly act as nutrients for photosynthetic organisms
(25).
Several bacterial and fungal species which can utilize
organophosphate pesticide derivatives were isolated from soil
in vitro. The fungal species like Aspergillus flaVus, Trichoderma
harzianum, and so forth and bacterial species like Pseudomonas,
Serratia micrococcus, and so forth utilized the above pesticides
as a phosphorus source and showed increased growth. The
number of colony-forming units were greatest with compound
7h, which indicated that this compound was more susceptible
to and easily degradable by the microorganisms (Table 5).
Hence, the results indicated that some of the microorganisms
were able to degrade the title compounds to nutritive phosphate
residues.
In summary, a simple and efficient synthesis is developed
for the title compounds 7a-k using Nb2O5 as a catalyst. Then,
compounds are found to have a lethal effect on whip smut of
sugarcane and at the same time acted as nutrients for the
sugarcane plants. Furthermore, the test compounds are ecof-
(13) Nene, Y. L.; Thapliyal, P. N. Evaluation of Fungicides.
Fungicides in plant disease control, 3rd ed.; Oxford & IBH
publishing Co. Pvt. Ltd.: New Delhi, India, 2002; pp 526-540.

Synthesis of Methanols and Their Bioactivity
J. Agric. Food Chem., Vol. 55, No. 17, 2007 6939
(14) Bilgrami, K. S; Dube, H.S. The Smuts and Bunts. A Text Book
of Modern Plant Pathology; Vikas Publishing House Pvt. Ltd.:
India, 1985; pp 226-244.
(15) Santra, S. C; Chatterjee, T. P; Das, A. P. Plant Biochemical
analysis (Quantitative). College Botany Practical; New Central
Book Agency (P) Ltd.: Calcutta, India, 1993; Vol. 1, pp 63-
75.
(16) Johnson, L. F.; Curi, E. A.; Bond, J. H.; Firiburg, H. Methods
for Studying Soil Micro Flora-Plants Disease Relationship, 2nd
ed.; Burges Publishing Company: Minneapolis, MN, 1960.
(17) Smith, N. R; Dawson, V. T. The bacteriostatic action of Rose
Bengal media used for the plate count of soil fungi. Soil Sci.
1944, 58, 467-471.
(18) Muthiah, C.; Praveen Kumar, K.; Arunmani, C.; Kumarswamy,
K. C. Chlorophosphonates: Inexpensive precursors for stereo-
defined chloro-substituted olefins and unsymmetrical disubsti-
tuted acetylenes. J. Org. Chem. 2000, 65, 3733-3737.
(19) Emsley, J.; Hal, D. Tricoordinate Organophosphorus Chemistry.
The Chemistry of Phosphorus; Harper and Row Publishers:
London, 1976; p 119.
(21) Juexiao, C.; Zhenghong, Z.; Guofeng, Z.; Chuchi, T. Convenient
synthesis of optically active R-hydroxyphosphinic acids. Het-
eroat. Chem. 2003, 14 (4), 312-315.
(22) Silverstein, R.M.; Webster, F.X. Spectrometric Identification of
Organic Compounds, 6th ed.; John Wiley & Sons, Inc.: New
York, 1998.
(23) Quin, L. D.; Venkade, J. G. Phosphorus 31 NMR Spectral
Properties in Compound Characterization and Structural Analy-
sis; VCH Publishers Inc.: New York, 1994.
(24) Manabchakravarty, B.; Srinivas, C.; Muthiah, C.; Kumarswamy,
K. C. Synthesis and utility of R-methoxy phosphonates with a
1,3,2-dioxaphosphorinane ring. Synthesis 2003, 15, 2368-2372.
(25) Kononova, S. V.; Nesmeyanova, M. A. Phosphonates and their
Degradation by Microorganisms. Biochemistry (Moscow) 2002,
67 (2), 184-195.
Received for review March 22, 2007. Revised manuscript received June
14, 2007. Accepted June 22, 2007. One author (Y.B.K.) is grateful to
UGC, New Delhi, for financial support.
(20) Richard, H. H.; Smits, K.; Sesham, J.; Ross, R. H. The selective
oxidative dehydrogenation of propane over niobium pentoxide.
J. Chem. Soc., Chem. Commun. 1991, 588-589.
JF070850Z