Simple synthesis of 3-acetamido-β-resorcylic acids as potential FabF and FabH inhibitors without using protecting groups

Article abstract of DOI:10.1055/s-0028-1087544

A simple two-step strategy for the synthesis of 3-acetamido-β- resorcylic acids as potential platensimycin analogues was developed. It avoids the use of protecting group chemistry and starts from 2-aminoresorcinol, which is first N-acylated and then subje

Full text of DOI:10.1055/s-0028-1087544

LETTER
437
Simple Synthesis of 3-Acetamido-b-resorcylic Acids as Potential FabF and
FabH Inhibitors without Using Protecting Groups
S
a
imple Synthesis
o
e
f
3-Acetam
n
ido-
b
-resorc
a
ylic Acidsd Maraš,a Petra Štefanič Anderluh,b Uroš Urleb,b Marijan Kočevar*a
Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, 1000 Ljubljana, Slovenia
Fax +386(1)2419220; E-mail: marijan.kocevar@fkkt.uni-lj.si
b
Lek Pharmaceuticals d.d., Verovškova 57, 1526 Ljubljana, Slovenia
Received 24 October 2008
synthesis starting from 2-nitroresorcinol (3) and applying
organolithium and protecting group chemistry (MOM,
Boc and TMS protections).2a The original amide synthetic
strategy for the preparation of 1a was to couple the appro-
Abstract: A simple two-step strategy for the synthesis of 3-acet-
amido-b-resorcylic acids as potential platensimycin analogues was
developed. It avoids the use of protecting group chemistry and starts
from 2-aminoresorcinol, which is first N-acylated and then subject-
ed to a modified Kolbe–Schmitt carboxylation to yield the desired priate acid with a several-fold excess of 2 using 2-(7-aza-
3-acetamido-b-resorcylic acids.
1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexa-
fluorophosphate (HATU) as a coupling reagent, followed
by the hydrolysis of ester and MOM protection groups.
Recently, a simple preparation of 3-nitro- and 3-amino-b-
resorcylic acid derivatives, starting from b-resorcylic acid
was published by Heretsch and Giannis.7 This strategy
was later applied in the preparation of 2-trimethylsilyl-
ethyl 3-amino-b-resorcylate used in a more recent total
synthesis of platensimycin by Nicolaou et al.8 These ap-
proaches certainly seem to be the most rational when
starting with precious carboxylic acids.
Key words: phenols, acylations, carboxylic acids, drugs, antibiot-
ics
Platensimycin (1a; Figure 1) isolated from Streptomyces
platensis was found to be an antibiotic, targeting highly
conserved bacterial FabF enzymes involved in fatty acid
biosynthesis.1 Several total and formal syntheses of
platensimycin were reported soon after its structural elu-
cidation was published.2 Recently, the literature on pla-
tensimycin synthesis was reviewed.3 Another very similar
compound, platencin (1b; Figure 1), was isolated from a
different strain of S. platensis and found to be a dual in-
hibitor of FabF and FabH.4 Several of their close ana-
logues, some with high antibacterial potency were also
published.5 The above compounds are essentially amides
between complex spirocyclic carboxylic acids and 3-ami-
no-b-resorcylic acid (1c; Figure 1). Platensimycin and
platencin are prominent lead compounds for developing
new, broad-spectrum antibiotics and it would be advanta-
geous from the point of view of medicinal chemistry to
identify the parts of platensimycin involved in the FabF
binding.6
CO2Me
OMOM
NH2
2
OMOM
Figure 2
On the other hand, it would be of interest to form various
amides without using protecting groups and to make the
synthesis as short as possible. For this reason we decided
to prepare a series of 3-acetamido-b-resorcylic acids start-
ing from simple, commercially available carboxylic acids
or acid chlorides using a new strategy that would allow us
to skip the protecting group chemistry.
O
O
O
R =
O
CO2H
The obvious way to avoid protecting the carboxy group is
to introduce it in the last synthetic step. The MOM protec-
tion of the hydroxy groups used in the first published
preparation of 22a is obsolete for the amide bond forma-
tion itself, because the N-acylation of aminophenols can
be carried out with high chemoselectivity over O-acyla-
tion. The MOM protection was only necessary for the
lithiation used to introduce the methoxycarbonyl group, a
step which becomes superfluous once the carboxy group
is introduced last. Moreover, during the preparation of this
manuscript, Hayashida and Rawal published their total
synthesis of racemic 1b, where they used unprotected 3-
amino-b-resorcylic acid (1c) in the amide-formation step
with DCC as the coupling agent.9 However, their synthe-
OH
Me
Me
R
N
H
Me
O
OH
1c: R = H
1a
1b
Figure 1
The synthesis of the protected 1c in the form of methyl 3-
amino-2,4-bis(methoxymethoxy)benzoate (2; Figure 2)
was first described by Nicolaou et al. using a five-step
SYNLETT 2009, No. 3, pp 0437–0440
Advanced online publication: 21.01.2009
x
x.
x
x.
2
0
0
9
DOI: 10.1055/s-0028-1087544; Art ID: G35608ST
© Georg Thieme Verlag Stuttgart · New York

438
N. Maraš et al.
LETTER
CO2H
OH
OH
OH
OH
a
c
b
NO2
NH2
NHCOR
NHCOR
OH
OH
OH
OH
3
4
5
6
Scheme 1 Reagents and conditions: (a) H2 (60 psi), Pd/C, EtOAc; (b) RCOCl, pyridine, EtOAc; or RCO2H, CDI, THF; or RCO2H, DCC,
THF, yield from 3 to 5 66–94%; (c) CO2, K2CO3, DMSO, 120 °C, 12 h, 15–52%.
Table 1 Preparation of Products 6
sis of 1c still required the use of protecting group chemis-
try.
Entry
1
R
Substrate Product Yield (%)a
To avoid the use of protecting groups, we carried out the
following reaction sequence: first we hydrogenated 2-
nitroresorcinol (3) to 2-aminoresorcinol (4), which was
found to readily react with acyl chlorides or carboxylic
acids activated with a coupling agent, yielding N-acylated
2-aminoresorcinols 5 (Scheme 1; Table 1).
5a
5b
6a
6b
25
50
2
3
5c
6c
30
25
Methods for the direct introduction of a carboxy group to
a phenol are quite limited, and so we considered two reac-
tions. The first is using CO2 in an electrophilic aromatic
substitution via a very old reaction known as the Kolbe–
Schmitt carboxylation,10 which became famous for its use
in the synthesis of salicylic acid as well as other industri-
ally important hydroxybenzoic acids. The second one is
the copper-catalyzed carboxylation of phenols with CCl4,
a reaction originally discovered by Reimer and Tie-
mann.11 Using N-(2,6-dihydroxyphenyl)-3,3-dimethyl-
butanamide (5a) as a test substrate, the carboxylation with
CCl4 failed under standard conditions12 and only gave tar-
ry products. The Kolbe–Schmitt carboxylation using
water as a solvent and either K2CO3 or Na2CO3 as a base
also failed, even though we used an autoclave in order to
maintain a high CO2 pressure and temperatures in the
range of 100–120 °C. Interestingly, even though there was
no conversion on our test compound 5a, we found that the
Kolbe–Schmitt carboxylation of 2-aminoresorcinol (4)
under the same conditions, at 110 °C for eight hours in
water and using K2CO3 as a base, gave a 15% conversion
to 1c (as shown on the basis of 1H NMR spectroscopy; the
product mixture also contained the unreacted starting ma-
terial). The lack of reactivity of our test substrate 5a is, to
some extent, surprising, because resorcinol itself reacts
easily in the Kolbe–Schmitt reaction in water even at at-
mospheric pressure and at the temperature of a steam bath
to give b-resorcylic acid in a 60% yield.13 The use of di-
glyme or isopropanol as co-solvents in water was also
checked, but without success. Apparently, the inductive
effect of the acylamino group deactivates our substrate
enough to be inert under such reaction conditions. It is
known that the presence of water inhibits the Kolbe–
Schmitt carboxylation; therefore, the less reactive sub-
strates are commonly carboxylated as preformed sodium
or potassium phenolates, either in the solid state or in a
suspension of high-boiling hydrocarbon solvents.10
Nevertheless, good results were also reported using phe-
nols with various bases in polar aprotic solvents.14 We
therefore chose DMSO as a solvent in the absence of wa-
4
5
5d
6d
O
5e
5f
6e
6f
32
52
O
O
6
7
8
5g
5h
6g
6h
20
22
NH
9
10
11
5i
6i
49
OMe
O
5j
5k
6j
6k
47
OH
15b
a Isolated yields are given (not taking into account the recovered start-
ing material).
b DCC was used in the anilide formation step. The yield is based on
2-nitroresorcinol, because 5k could not be properly purified from the
N,N¢-dicyclohexylurea remains.
ter. We found that by using K2CO3 as a base in DMSO at
110–120 °C our substrate 5a was carboxylated to 6a,
which was isolated in a 25% yield. When reactions were
performed with a series of substrates 5b–l we similarly
isolated products 6b–l in 15–52% yields (Table 1).15 We
Synlett 2009, No. 3, 437–440 © Thieme Stuttgart · New York

LETTER
Simple Synthesis of 3-Acetamido-b-resorcylic Acids
439
(2) (a) Nicolaou, K. C.; Li, A.; Edmonds, D. J. Angew. Chem.
Int. Ed. 2006, 45, 7086. (b) Zou, Y.; Chen, C.-H.; Taylor,
C. D.; Foxman, B. M.; Snider, B. B. Org. Lett. 2007, 9,
1825. (c) Nicolaou, K. C.; Tang, Y.; Wang, J. Chem.
Commun. 2007, 1922. (d) Nicolaou, K. C.; Edmonds, D. J.;
Li, A.; Scott Tria, G. Angew. Chem. Int. Ed. 2007, 46, 3942.
(e) Matsuo, J.; Takeuchi, K.; Ishibashi, H. Org. Lett. 2008,
10, 4049. (f) Lalic, G.; Corey, E. J. Org. Lett. 2007, 9, 4921.
(g) Tiefenbacher, K.; Mulzer, J. Angew. Chem. Int. Ed. 2007,
46, 8074. (h) Ghosh, A. K.; Xi, K. Org. Lett. 2007, 9, 4013.
(i) Li, P.; Payette, J. N.; Yamamoto, H. J. Am. Chem. Soc.
2007, 129, 9534.
also found that in most cases the majority of the unreacted
starting material 5 can be recycled. The reactions were not
completely optimized, but they were shown to give repro-
ducible yields of products.
2-Nitroresorcinol (3) was hydrogenated to 2-aminoresor-
cinol (4) using palladium on carbon in ethyl acetate as a
solvent; the catalyst was filtered off, the filtrate split into
several aliquots ready for acylations with acid chlorides or
acids activated generally with carbonyldiimidazole
(CDI). The so-obtained N-(2,6-dihydroxyphenyl)amides
5 were used in the modified Kolbe–Schmitt carboxylation
at 120 °C with DMSO as a solvent and in an autoclave
charged with dry ice as a source of CO2. The isolation
generally consisted of an extraction of the reaction mix-
ture diluted with water to separate the unreacted starting
material, followed by an acidification to isolate the acidic
product 6, which was then further purified by either re-
crystallization or radial chromatography. The adamantyl
derivative 6h required a modified isolation, because it was
found that the product was fully extracted from the basic
aqueous mixture with ethyl acetate, presumably still in the
form of the potassium salt. Thus, the reaction mixture
containing 6h was first acidified and the product and start-
ing material were extracted into ethyl acetate, from which
the product was separated by extraction into aqueous am-
monia.
(3) Tiefenbacher, K.; Mulzer, J. Angew. Chem. Int. Ed. 2008,
47, 2548.
(4) (a) Jayasuriya, H.; Herath, K. B.; Zhang, C.; Zink, D. L.;
Basilio, A.; Genilloud, O.; Diez, M. T.; Vicente, F.;
Gonzalez, I.; Salazar, O.; Pelaez, F.; Cummings, R.; Ha, S.;
Wang, J.; Singh, S. B. Angew. Chem. Int. Ed. 2007, 46,
4684. (b) Basilio, A.; Genilloud, O.; Jayasuriya, H.;
Gonzalez, I.; Singh, S. B.; Salazar, O.; Wang, J. Int. Patent,
WO2005115400, 2005; Chem. Abstr. 2005, 144, 5523.
(5) (a) Nicolaou, K. C.; Lister, T.; Denton, R. M.; Montero, A.;
Edmonds, D. J. Angew. Chem. Int. Ed. 2007, 46, 4712.
(b) Nicolaou, K. C.; Tang, Y.; Wang, J.; Stepan, A. F.; Li,
A.; Montero, A. J. Am. Chem. Soc. 2007, 129, 14850.
(c) Singh, S. B.; Herath, K. B.; Wang, J.; Tsou, N.; Ball,
R. G. Tetrahedron Lett. 2007, 48, 5429. (d) Yeung, Y.-Y.;
Corey, E. J. Org. Lett. 2008, 10, 3877.
(6) Häbich, D.; von Nussbaum, F. ChemMedChem 2006, 1, 951.
(7) Heretsch, P.; Giannis, A. Synthesis 2007, 2614.
(8) Nicolaou, K. C.; Tria, G. S.; Edmonds, D. J. Angew. Chem.
Int. Ed. 2008, 47, 1780.
(9) Hayashida, J.; Rawal, V. H. Angew. Chem. Int. Ed. 2008, 47,
4373.
In conclusion, we have developed a simple, short reaction
sequence for the preparation of 3-acetamido-b-resorcylic
acids without applying protecting groups. The method in-
cludes a modified Kolbe–Schmitt carboxylation using
DMSO as a solvent and K2CO3 as a base. This synthetic
strategy allows the preparation of a library of compounds
for potential FabF and FabH inhibitors screening.
(10) Lindsey, A. S.; Jeskey, H. Chem. Rev. 1957, 57, 583.
(11) Reimer, K.; Tiemann, F. Ber. Dtsch. Chem. Ges. 1876, 9,
1285.
(12) Sasson, Y.; Razintsky, M. J. Chem. Soc., Chem. Commun.
1985, 1134.
(13) Nierenstein, M.; Clibbens, D. A. Org. Synth., Coll. Vol. II;
Wiley: New York, 1943, 557.
(14) Meek, W. H.; Fuchsman, C. H. J. Chem. Eng. Data 1969, 14,
Acknowledgment
388.
We thank Lek Pharmaceuticals d.d., the Ministry of Higher Educa-
tion, Science and Technology of the Republic of Slovenia and the
Slovenian Research Agency for financial support (P1-0230-0103).
Dr. B. Kralj and Dr. D. Žigon (Center for Mass Spectroscopy, ‘Jožef
Stefan’ Institute, Ljubljana, Slovenia) are gratefully acknowledged
for the mass spectrometric measurement.
(15) General Procedure for the Preparation of N-Acyl-2,6-
dihydroxyanilines 5a–e Using Acid Chlorides: To a
solution of 2-aminoresorcinol (4; 7 mmol) in EtOAc (30 mL)
stirred in an ice bath was added pyridine (0.76 mL, 10 mmol)
followed a dropwise introduction of a solution of an acid
chloride (6 mmol) in EtOAc (30 mL). After 1 h the reaction
mixture was washed with H2O (30 mL), aq NaHCO3 (5%, 30
mL), aq HCl (1 M, 30 mL), H2O (30 mL), then dried over
Na2SO4 and evaporated in vacuo yielding 5.
References and Notes
(1) (a) Wang, J.; Soisson, S. M.; Young, K.; Shoop, W.; Kodali,
S.; Galgoci, A.; Painter, R.; Parthasarathy, G.; Tang, Y. S.;
Cummings, R.; Ha, S.; Dorso, K.; Motyl, M.; Jayasuriya, H.;
Ondeyka, J.; Herath, K.; Zhang, C.; Hernandez, L.; Allocco,
J.; Basilio, ; Tormo, J. R.; Genilloud, O.; Vicente, F.; Pelaez,
F.; Colwell, L.; Lee, S. H.; Michael, B.; Felcetto, T.; Gill, C.;
Silver, L. L.; Hermes, J. D.; Bartizal, K.; Barrett, J.;
Schmatz, D.; Becker, J. W.; Cully, D.; Singh, S. B. Nature
(London) 2006, 441, 358. (b) Singh, S. B.; Jayasuriya, H.;
Ondeyka, J. G.; Herath, K. B.; Zhang, C.; Zink, D. L.; Tsou,
N. N.; Ball, R. G.; Basilio, A.; Genilloud, O.; Diez, M. T.;
Vicente, F.; Pelaez, F.; Young, K.; Wang, J. J. Am. Chem.
Soc. 2006, 128, 11916. (c) Basilio, A.; Genilloud, O.;
Hernandez, P.; Singh, S. B.; Tormo, J. R.; Wang, J. Int.
Patent, WO2005009391, 2005; Chem. Abstr. 2005, 142,
196607.
General Procedure for the Preparation of N-Acyl-2,6-
dihydroxyanilines 5f–j Using Acids and CDI: To a
solution of a carboxylic acid (1.16 g, 6 mmol) in THF (10
mL) was added carbonyldiimidazole (1.00 g, 6 mmol). After
stirring for 1 h at r.t., it was added to a solution of 2-
aminoresorcinol (4) (7 mmol) in EtOAc (30 mL). The
mixture was left stirring for 24 h at r.t., washed with diluted
hydrochloric acid (3%; 30 mL), aq NaHCO3 (3%; 30 mL),
H2O (30 mL), dried over Na2SO4 and evaporated in vacuo to
give 5.
General Procedure for the Kolbe–Schmitt Carboxy-
lation: To the solution of 5 (4 mmol) in DMSO (35 mL) in
an autoclave (300 mL size) was added anhyd K2CO3 (1.70 g,
12 mmol) followed by the addition of dry ice (CO2; ca. 20 g).
The autoclave was immediately closed and heated at 120 °C
Synlett 2009, No. 3, 437–440 © Thieme Stuttgart · New York

440
N. Maraš et al.
LETTER
for 12 h. After carefully opening the autoclave, in order to
release the CO2 pressure, the reaction mixture was diluted
with H2O (100 mL) and extracted with EtOAc (4 × 30 mL).
The extract was washed with NaHCO3 (3%, 30 mL), H2O
(30 mL), dried over Na2SO4 and evaporated in vacuo to give
the unreacted starting material 5. The diluted reaction
mixture was then acidified with hydrochloric acid (to pH ca.
3), saturated with NaCl and extracted with EtOAc (4 × 30
mL). The extract was washed with brine (30 mL), dried over
Na2SO4 and evaporated in vacuo to give a crude product 6,
which was further purified.
3-[(3,3-Dimethylbutanoyl)amino]-2,4-dihydroxybenzoic
Acid (6a): crystalline solid (25% yield); mp 198–200 °C
(dec.). 1H NMR (DMSO-d6): d = 1.04 (s, 9 H, t-Bu), 2.21 (s,
2 H, CH2), 6.43 (d, J = 8.8 Hz, 1 H, ArH), 7.56 (d, J = 8.8
Hz, 1 H, ArH), 8.91 (s, 1 H, NH), 10.21 (s, 1 H, OH), 11.81
(br s, 1 H, OH), 12.60–14.40 (br s, 1 H, CO2H). 13C NMR
(DMSO-d6): d = 29.6, 30.6, 48.7, 104.4, 107.9, 113.0, 128.8,
158.8, 159.0, 170.7, 172.2. IR (KBr): 1642, 1533, 1437,
1379, 1253 cm–1. MS (EI): m/z = 267 (24) [M+], 169 (54),
151 (100), 125 (28). Anal. Calcd for C13H17NO5: C, 58.42;
H, 6.41; N, 5.24. Found: C, 58.69; H, 6.69; N, 5.15.
3-[(Adamantan-1-ylacetyl)amino]-2,4-dihydroxybenzoic
Acid (6h): mp >180 °C (dec.). 1H NMR (DMSO-d6): d =
1.55–1.72 (m, 12 H, 6 × adamantyl CH2), 1.89–1.97 (m, 3 H,
3 × adamantyl CH), 2.10 (s, 2 H, CH2), 6.43 (d, J = 8.8 Hz,
1 H, ArH), 7.56 (d, J = 8.8 Hz, 1 H, ArH), 8.91 (s, 1 H, NH),
10.23 (s, 1 H, OH), 11.84 (br s, 1 H, OH), 13.46 (br s, 1 H,
CO2H). 13C NMR (DMSO-d6): d = 28.0, 32.4, 36.4, 41.9,
49.7, 104.3, 108.0, 113.1, 128.7, 158.6, 158.8, 170.0, 172.2.
IR (KBr): 1709, 1641, 1536, 1449, 1395, 1269 cm–1. MS
(ESI): m/z = 346 [MH+]. HRMS (ESI): m/z [M + H]+ calcd
for C19H24NO5: 346.1654; found: 346.1662. Anal. Calcd for
C19H23NO5: C, 66.07; H, 6.71; N, 4.06. Found: C, 66.34; H,
7.02; N, 3.92.
2,4-Dihydroxy-3-[({[1R-(2-endo,3-exo)]-3-hydroxy-4,7,7-
trimethylbicyclo[2.2.1]hept-2-yl}acetyl)amino]benzoic
Acid (6k): white powder (15% yield); mp 167–169 °C. 1H
NMR (DMSO-d6): d = 0.78 (s, 3 H, Me), 0.81 (s, 3 H, Me),
1.03 (s, 3 H, Me), 0.91 (m, 2 H), 1.35–1.51 (m, 3 H), 1.64
(br, 1 H), 2.30–2.43 (m, 2 H), 3.07 (br, 1 H, CH2,
bicycloheptyl), 4.62 (br s, 1 H, OH), 6.43 (d, J = 8.8 Hz, 1 H,
ArH), 7.57 (d, J = 8.8 Hz, 1 H, ArH), 9.10 (s, 1 H, NH),
10.10 (s, 1 H, OH), 11.84 (br s, 1 H, OH), 13.5 (br s, 1 H,
CO2H). 13C NMR (DMSO-d6): d = 11.7, 19.6, 20.0, 20.7,
34.1, 36.9, 46.0, 47.0, 47.8, 49.0, 83.7, 104.4, 107.9, 112.8,
128.8, 158.6, 158.8, 172.1, 172.2. IR (KBr): 1645, 1541,
1383, 1296, 1248 cm–1. MS (ESI): m/z = 364 [MH+]. HRMS
(ESI): m/z [M + H]+ calcd for C19H26NO6: 364.1760; found:
364.1772.
All the products gave satisfactory analytical and
spectroscopic data.
Selected Characterization Data for the Representative
Products:
N-(2,6-Dihydroxyphenyl)-3,3-dimethylbutanamide (5a):
off-white product (84% yield); mp 164–167 °C. 1H NMR
(DMSO-d6): d = 1.04 (s, 9 H, t-Bu), 2.36 (s, 2 H, CH2CO),
6.38 (d, J = 8.1 Hz, 2 H, ArH), 6.88 (t, J = 8.1 Hz, 1 H, ArH),
9.28 (s, 1 H, NH), 9.41 (s, 2 H, 2 × OH). 13C NMR (DMSO-
d6): d = 29.6, 30.7, 48.3, 107.8, 114.5, 126.4, 151.5, 172.1.
IR (KBr): 1637, 1591, 1536, 1481, 1371 cm–1. MS (EI): m/z
= 223 (14) [M+], 125 (100). HRMS (EI): m/z [M]+ calcd for
C12H17NO3: 223.1208; found: 223.1216. Anal. Calcd for
C12H17NO3: C, 64.55; H, 7.67; N, 6.27. Found: C, 64.79; H,
7.83; N, 6.09.
N-(2,6-Dihydroxyphenyl)-5-oxohexanamide (5g): off-
white crystalline product (77% yield); mp 128–131 °C. 1H
NMR (DMSO-d6): d = 1.77 (m, 2 H, CH2), 2.09 (s, 3 H, Me),
2.39 (t, J = 7.3 Hz, 2 H, CH2), 2.51 (t, J = 7.3 Hz, 2 H, CH2),
6.34 (d, J = 8.1 Hz, 1 H, ArH), 6.87 (t, J = 8.1 Hz, 2 H, ArH),
9.22 (s, 1 H, NH), 9.29 (s, 2 H, OH). 13C NMR (DMSO-d6):
d = 19.5, 29.7, 34.3, 41.8, 107.5, 113.9, 126.5, 152.0, 172.7,
208.0. IR (KBr): 1692, 1645, 1605, 1536, 1379 cm–1. MS
(EI): m/z (%) = 237 (7) [M+], 125 (100), 113 (10), 85 (20).
HRMS (EI): m/z calcd for C12H15NO4: 237.1001; found:
237.1006. Anal. Calcd for C12H15NO4: C, 60.75; H, 6.37; N,
5.90. Found: C, 60.85; H, 6.44; N, 5.87.
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