Synthesis of heterocycles on the basis of arylation products of unsaturated compounds. 11.1 5-R-benzyl-2-iminoselenazolidin-4-ones from ethyl 3-aryl-2-bromopropanoates

Article abstract of DOI:10.1080/10426500490257096

Ethyl 3-aryl-2-bromopropanoates 2a-p were prepared by reaction of ethyl acrylate with arenediazonium bromides 1a-p in the presence of CuBr (Meerwein arylation). These compounds react with selenourea to form 5-R-benzyl-2- iminoselenazolidin-4-ones 4a-p. Compounds 4a-p hydrolyze into the corresponding selenazolidin-2,4-diones.

Full text of DOI:10.1080/10426500490257096

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SYNTHESIS OF HETEROCYCLES ON THE BASIS OF
ARYLATION PRODUCTS OF UNSATURATED COMPOUNDS.
11. 5-R-BENZYL-2- IMINOSELENAZOLIDIN-4-ONES FROM
ETHYL 3-ARYL-2-BROMOPROPANOATES
Mykola D. Obushak a , Vasyl S. Matiychuk a , Volodymyr M. Tsyalkovsky a & Roman M.
Voloshchuk a
a Department of Organic Chemistry, Ivan Franko National University of Lviv, Lviv, Ukraine
Available online: 11 Aug 2010
To cite this article: Mykola D. Obushak, Vasyl S. Matiychuk, Volodymyr M. Tsyalkovsky & Roman M. Voloshchuk (2004):
SYNTHESIS OF HETEROCYCLES ON THE BASIS OF ARYLATION PRODUCTS OF UNSATURATED COMPOUNDS. 11. 5-R-BENZYL-2-
IMINOSELENAZOLIDIN-4-ONES FROM ETHYL 3-ARYL-2-BROMOPROPANOATES, Phosphorus, Sulfur, and Silicon and the Related
Elements, 179:1, 107-113
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Phosphorus, Sulfur, and Silicon, 179:107–113, 2004
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Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500490257096
SYNTHESIS OF HETEROCYCLES ON THE BASIS
OF ARYLATION PRODUCTS OF UNSATURATED
COMPOUNDS. 11.1 5-R-BENZYL-2-
IMINOSELENAZOLIDIN-4-ONES FROM ETHYL
3-ARYL-2-BROMOPROPANOATES
Mykola D. Obushak, Vasyl S. Matiychuk, Volodymyr M.
Tsyalkovsky, and Roman M. Voloshchuk
Department of Organic Chemistry, Ivan Franko National
University of Lviv, Lviv, Ukraine
(Received June 2, 2003; accepted July 27, 2003)
Ethyl 3-aryl-2-bromopropanoates 2a–p were prepared by reaction of
ethyl acrylate with arenediazonium bromides 1a–p in the presence of
CuBr (Meerwein arylation). These compounds react with selenourea to
form 5-R-benzyl-2-iminoselenazolidin-4-ones 4a–p. Compounds 4a–p
hydrolyze into the corresponding selenazolidin-2,4-diones.
Keywords: 2-iminoselenazolidin-4-one; cyclization; Meerwein aryla-
tion; selenazole; selenazolidin-2,4-dione; selenourea
Organoselenium compounds permanently attract attention of chemists;
this may be conditioned on their interesting reactivities and potential
pharmaceutical significance. A special place among these compounds
take selenium-containing heterocycles.
Much of the interest in synthesis of selenazole derivatives is due to
their biological activities.2–6 A convenient method to obtain the substi-
tuted selenazoles is the interaction between α-haloketones with com-
pounds containing a selenoamide fragment—H2NC(Se)R.2,3,7–14 The
interaction of these compounds with α-halogenocarboxylic acids and
their derivatives to yield selenazolidin-4-ones have been studied con-
siderably less.15,16
We suggest an approach to synthesis of selenazolidin-4-one deriva-
tives through the products of Meerwein arylation of acrylates. Arene-
diazonium bromides 1a–p react with ethyl acrylate in acetone in the
Address correspondence to Mykola D. Obushak, Department of Organic Chemistry,
Ivan Franko National University of Lviv, Kyryla & Mefodiya 6, Lviv 79005, Ukraine.
E-mail: obushak@in.lviv.ua
107

108
M. D. Obushak et al.
presence of CuBr yielding ethyl 3-aryl-2-bromopropanoates 2a–p
(Scheme 1). We have reported the synthesis of similar compounds
earlier.17 They are obtained in 40–60% yield.
SCHEME 1
It has been established that esters 2a–p react with selenourea form-
ing selenazole rings. Selenourea alkylated by α-bromoesters while boil-
ing in ethanol in the presence of pyridine, affords selenouronium salts
3a–p. Under the conditions of reaction they have cyclized to give 5-R-
benzyl-2-iminoselenazolidin-4-ones 4a–p in high yields (Scheme 2).
SCHEME 2
It is necessary to stress, that the compounds 2a–p in the presence of
bases can eliminate HBr forming cinnamic esters. However, under the
given conditions we can escape such a reaction.
In this reaction selenourea is more efficient than thiourea:17 reaction
times are up 20–30 min and 2–3 h respectively.

Iminoselenazolidines
109
Compounds of this type are characterized by imino-amino
tautomerism.16 According to 1H NMR spectra in DMSO-d6 compounds
4a–p exist in imino form (two signals of NH groups app. ∼8.5 and
∼9.0 ppm).
The described method of designing a selenazolidine cycle is the first
which gives the opportunity to obtain selenazole derivatives containing
benzyl substituents. Besides, the availability of an amidine fragment
makes it possible to utilize these compounds as a reagents in reactions
of various types.
Thus, the performed research demonstrated the possibility to obtain
5-R-benzyl substituted selenazoles through the products of bromoary-
lation of acrylates. Selenazoles 4a–p can be easily transformed into the
corresponding selenazolidin-1,4-diones.
SCHEME 3
The prepared compounds seem to be interesting for biological activity
studies. It is worth mentioning that among 5-R-benzylthiazolidin-4-
ones a range of antidiabetic agents is known.18,19
EXPERIMENTAL
All melting points are uncorrected. The 1H NMR spectra were recorded
on a Bruker 400 MHz (compounds 4c,e,i,k,m,p; 5a,b) or Bruker DRX
500 MHz (compounds 4a,b,d,f–h,g,l,n,o) spectrometers in DMSO-d6.
Chemical shifts are reported in ppm relative to the residual signal of the
solvent. Coupling constants (J) are indicated in Hz. Mass spectra were
obtained using a Finnigan MAT INKOS-50 chromatomass spectrometer
at 70 eV.
General Procedure for the Synthesis of Ethyl
3-Aryl-2-bromopropanoates (2a--p)
A solution of NaNO2 (16.6 g, 0.24 mmol) in H2O (30 ml) was added
dropwise to a stirred and ice-cooled mixture of the substituted aniline
(0.22 mmol), aqueous HBr (47%, 95 g, 0.55 mmol), and water (30 ml)

110
M. D. Obushak et al.
below 0–5◦C. The cold diazonium salt solution is slowly added to the vig-
orously stirred solution of CuBr (3 g, 21 mmol) and ethyl acrylate (22.0 g,
0.22 mmol) in acetone (150 ml) at 40◦C. The reaction is exothermic and
the dropping rate is adjusted at such a rate that nitrogen is evolved
at 2–3 bubbles/sec (0.5–1 h). The resultant homogeneous solution is
stirred for 30 min at 40◦C and diluted with H2O. The organic phase is
dried with MgSO4, and concentrated. The residue is purified by distil-
lation under reduced pressure to give ethyl 3-aryl-2-bromopropanoates
(40–60% yield).
General Procedure for the Synthesis
of 5-R-benzyl-2-iminoselenazolidin-4-ones (4a--p)
A mixture of 2a–p (4.1 mmol), pyridine (0.32 g, 4.1 mmol), selenourea
(0.5 g, 4.1 mmol), and ethanol (15 ml) was refluxed for 20–30 min. After
cooling, the crystals were collected by filtration and recrystallized from
EtOH/DMF to give the title compounds.
5-Benzyl-2-iminoselenazolidin-4-one (4a). m.p. 202–203◦C in 80%
1
2
3
yield. H NMR ppm: δ 2.95 (dd, 1H, CH2, J 14.0, J 11.0), 3.64 (dd,
3
1H, CH2, J 3.7), 4.67 (dd, 1H, CH), 7.16–7.28 (m, 5H, C6H5), 8.53 (s,
1H, NH), 8.92 (br. s, 1H, NH). Anal. requires for C10H10N2OSe (253.16)
calcd./found: C, 47.44/47.29; H, 3.98/3.93; N, 11.07/11.03.
5-(2-Methylbenzyl)-2-iminoselenazolidin-4-one (4b). m.p. 208–210◦C
1
2
in 66% yield. H NMR ppm: δ 2.38 (s, 3H, CH3), 2.93 (dd, 1H, CH2, J
3
3
14.7, J 11.6), 3.72 (dd, 1H, CH2, J 3.7), 4.65 (dd, 1H, CH), 7.06–7.17
(m, 4H, C6H4), 8.55 (s, 1H, NH), 8.95 (br. s, 1H, NH). Anal. requires
for C11H12N2OSe (267.19) calcd./found: C, 49.45/49.38; H, 4.53/4.45;
N, 10.48/10.59.
5-(3-Methylbenzyl)-2-iminoselenazolidin-4-one (4c). m.p. 181–182◦C
1
2
in 75% yield. H NMR ppm: δ 2.31 (s, 3H, CH3), 2.87 (dd, 1H, CH2, J
3
3
14.0, J 11.2), 3.58 (dd, 1H, CH2, J 3.6), 4.70 (dd, 1H, CH), 6.98–7.04
(m, 3H, C6H4), 7.15 (t, 1H, C6H4), 8.71 (s, 1H, NH), 9.08 (br. s, NH;
exchangeable). Anal. requires for C11H12N2OSe (267.19) calcd./found:
C, 49.45/49.57; H, 4.53/4.51; N, 10.48/10.40.
5-(4-Methylbenzyl)-2-iminoselenazolidin-4-one (4d). m.p. 207◦C in
1
2
73% yield. H NMR ppm: δ 2.31 (s, 3H, CH3), 2.91 (dd, 1H, CH2, J
14.1, 3J 10.8), 3.60 (dd, 1H, CH2, 3J 3.9), 4.64 (dd, 1H, CH), 7.05 (d, 2H,
C6H4, 3J 7.2), 7.10 (d, 2H, C6H4), 8.52 (s, 1H, NH), 8.90 (br. s, 1H, NH).
Anal. requires for C11H12N2OSe (267.19) calcd./found: C, 49.45/49.31;
H, 4.53/4.49; N, 10.48/10.45.
5-(4-Ethylbenzyl)-2-iminoselenazolidin-4-one (4e). m.p. 184–185◦C
1
in 75% yield. H NMR ppm: δ 1.21 (t, 3H, CH3), 2.59 (q, 2H, CH2),
2.89 (dd, 1H, CH2, 2J 14.4, 3J 10.8), 3.57 (dd, 1H, CH2, 3J 4.0), 4.70 (dd,

Iminoselenazolidines
111
1H, CH), 7.09 (d, 2H, C6H4, 3J 8.4), 7.12 (d, 2H, C6H4), 8.77 (br. s, NH;
exchangeable). Anal. requires for C12H14N2OSe (281.21) calcd./found:
C, 51.25/51.18; H, 5.02/4.91; N, 9.96/9.89.
5-(4-Butylbenzyl)-2-iminoselenazolidin-4-one (4f). m.p. 195◦C in 80%
1
yield. H NMR ppm: δ 0.94 (t, 3H, CH3), 1.36 (m, 2H, CH2), 1.59 (m,
2
3
2H, CH2), 2.56 (t, 2H, CH2), 2.90 (dd, 1H, CH2, J 14.0, J 10.8), 3.62
3
3
(dd, 1H, CH2, J 3.7), 4.63 (dd, 1H, CH), 7.05 (d, 2H, C6H4, J 7.9),
7.11 (d, 2H, C6H4, 3J 7.9), 8.54 (s, 1H, NH), 8.95 (br. s, 1H, NH).
Anal. requires for C14H18N2OSe (309.27) calcd./found: C, 54.37/54.23;
H, 5.87/5.82; N, 9.06/9.11.
5-(4-Fluorobenzyl)-2-iminoselenazolidin-4-one (4g). m.p. 189–191◦C
1
2
3
in 78% yield. H NMR ppm: δ 3.00 (dd, 1H, CH2, J 14.4, J 7.6), 3.58
(dd, 1H, CH2, 3J 4.4), 4.68 (dd, 1H, CH), 7.03–7.09 (m, 2H, C6H4),
7.24–7.29 (m, 2H, C6H4), 8.63 (br. s, NH; exchangeable). Anal. requires
for C10H9FN2OSe (271.15) calcd./found: C, 44.30/44.20; H, 3.35/3.27;
N, 10.33/10.24.
5-(2-Chlorobenzyl)-2-iminoselenazolidin-4-one (4h). m.p. 193–194◦C
in 83% yield. 1H NMR ppm: δ 3.07 (dd, 1H, CH2, 2J 14.4, 3J 10.5), 3.80
(dd, 1H, CH2, 3J 3.6), 4.78 (dd, 1H, CH), 7.18–7.26 (m, 2H, C6H4), 7.31
(d, 1H, C6H4), 7.35 (d, 1H, C6H4), 8.60 (s, 1H, NH), 9.02 (br. s, 1H, NH).
Anal. requires for C10H9ClN2OSe (287.60) calcd./found: C, 41.76/41.84;
H, 3.15/3.20; N, 9.74/9.63.
5-(4-Chlorobenzyl)-2-iminoselenazolidin-4-one (4i). m.p. 208–209◦C
in 74% yield. 1H NMR ppm: δ 2.98 (dd, 1H, CH2, 2J 14.4, 3J 10.0), 3.54
(dd, 1H, CH2, 3J 4.4), 4.74 (dd, 1H, CH), 7.23 (d, 2H, C6H4, 3J 8.0), 7.28
(d, 2H, C6H4), 8.69 (s, 1H, NH), 9.07 (br. s, 1H, NH). Anal. requires
for C10H9ClN2OSe (287.60) calcd./found: C, 41.76/41.63; H, 3.15/3.07;
N, 9.74/9.71.
5-(4-Bromobenzyl)-2-iminoselenazolidin-4-one (4j). m.p. 196–198◦C
in 78% yield. 1H NMR ppm: δ 2.99 (dd, 1H, CH2, 2J 14.3, 3J 10.4), 3.56
3
(dd, 1H, CH2, J 3.7), 4.67 (dd, 1H, CH), 7.17 (d, 2H, C6H4), 7.40 (d,
2H, C6H4), 8.60 (s, 1H, NH), 8.95 (br. s, 1H, NH). Mass: (70 eV) m/z
(%): 334 (M+ + 2, 18), 332 (M+, 24), 330 (11), 211 (39), 209 (40), 183
(54), 182 (30), 181 (28), 180 (18), 179 (12), 171 (100), 169 (98), 103 (25),
102 (48), 101 (10), 91 (22), 90 (40), 89 (32), 80 (11). Anal. requires for
C10H9BrN2OSe (332.06) calcd./found: C, 36.17/36.09; H, 2.73/2.79; N,
8.44/8.55.
5-(3-Nitrobenzyl)-2-iminoselenazolidin-4-one (4k). m.p. 205–206◦C
1
2
3
in 84% yield. H NMR ppm: δ 3.22 (dd, 1H, CH2, J 14.4, J 8.8), 3.62
(dd, 1H, CH2, 3J 4.4), 4.85 (dd, 1H, CH), 7.57 (t, 1H, C6H4), 7.68 (d, 1H,
C6H4, 3J 7.6), 8.08 (d, 1H, C6H4, 3J 8.0), 8.10 (s, 1H, C6H4), 8.70 (s, 1H,
NH), 9.08 (br. s, 1H, NH). Anal. requires for C10H9N3O3Se (298.16)
calcd./found: C, 40.28/40.04; H, 3.04/3.01; N, 14.09/14.12.

112
M. D. Obushak et al.
5-(4-Ethyloxycarbonylbenzyl)-2-iminoselenazolidin-4-one (4l). m.p.
1
197–198◦C in 65% yield. H NMR ppm: δ 1.38 (t, 3H, CH3), 3.08 (dd,
1H, CH2, 2J 14.0, 3J 10.4), 3.68 (dd, 1H, CH2, 3J 3.7), 4.32 (q, 2H, CH2),
3
3
4.73 (dd, 1H, CH), 7.34 (d, 2H, C6H4, J 7.9), 7.90 (d, 2H, C6H4, J
8.5), 8.70 (br. s, NH; exchangeable). Anal. requires for C13H14N2O3Se
(325.22) calcd./found: C, 48.01/47.94; H, 4.34/4.27; N, 8.61/8.50.
5-(4-Methoxybenzyl)-2-iminoselenazolidin-4-one (4m). m.p. 188–
1
2
3
189◦C in 68% yield. H NMR ppm: δ 2.88 (dd, 1H, CH2, J 14.0, J
3
10.8), 3.51 (dd, 1H, CH2, J 4.0), 3.74 (s, 3H, CH3), 4.70 (dd, 1H, CH),
6.80 (d, 2H, C6H4, J 8.4), 7.12 (d, 2H, C6H4), 8.67 (s, 1H, NH), 9.03
3
(br. s, 1H, NH). Anal. requires for C11H12N2O2Se (283.19) calcd./found:
C, 46.66/46.49; H, 4.27/4.22; N, 9.89/9.99.
5-(2,3-Dichlorobenzyl)-2-iminoselenazolidin-4-one (4n). m.p. 204–
1
2
3
206◦C in 67% yield. H NMR ppm: δ 3.15 (dd, 1H, CH2, J 14.0, J
10.4), 3.83 (dd, 1H, CH2, 3J 4.3), 4.76 (dd, 1H, CH), 7.23 (t, 1H, C6H3),
7.28 (d, 1H, C6H3, 3J 7.3), 7.41 (d, 1H, C6H3, 3J 7.9), 8.63 (s, 1H, NH),
9.03 (br. s, 1H, NH). Mass: (70 eV) m/z (%): 324 (M++2, 1.3), 322 (M+,
2), 320 (0.8), 289 (24), 287 (58), 285 (28), 219 (40), 217 (100), 215 (49),
182 (28), 161 (35), 159 (57), 136 (21), 102 (21), 89 (25), 75 (25). Anal.
requires for C10H8Cl2N2OSe (322.05) calcd./found: C, 37.30/37.29; H,
2.50/2.50; N, 8.70/8.70.
5-(2,5-Dichlorobenzyl)-2-iminoselenazolidin-4-one (4o). m.p. 217–
1
2
3
218◦C in 72% yield. H NMR ppm: δ 3.10 (dd, 1H, CH2, J 14.7, J
10.4), 3.75 (dd, 1H, CH2, 3J 4.3), 4.76 (m, 1H, CH), 7.23 (dd, 1H, C6H3,
3J 8.6, J 1.2), 7.33–7.37 (m, 2H, C6H3), 8.59 (s, 1H, NH), 9.00 (br. s,
4
1H, NH). Anal. requires for C10H8Cl2N2OSe (322.05) calcd./found: C,
37.30/37.18; H, 2.50/2.42; N, 8.70/8.82.
5-(3-Chloro-4-methylbenzyl)-2-iminoselenazolidin-4-one (4p). m.p.
1
196◦C in 70% yield. H NMR ppm: δ 2.31 (s, 3H, CH3), 2.95 (dd, 1H,
CH2, 2J 14.0, 3J 10.0), 3.51 (dd, 1H, CH2, 3J 4.0), 4.74 (dd, 1H, CH), 7.07
3
4
3
(dd, 1H, C6H3, J 8.0, J 1.4), 7.20 (d, 1H, C6H3, J 8.0), 7.23 (d, 1H,
4
C6H3, J 1.4), 8.73 (s, 1H, NH), 9.10 (br. s, NH; exchangeable). Anal.
requires for C11H11ClN2OSe (301.64) calcd./found: C, 43.80/43.71; H,
3.68/3.58; N, 9.29/9.33.
General Procedure for the Synthesis
of 5-R-benzylselenazolidin-1,4-diones (5a,b)
A mixture of 5-R-benzyl-2-iminoselenazolidin-4-one (6.0 mmol) in con-
centrated hydrochloric acid (15 ml) was refluxed for 3 h and cooled. The
crystals were collected by filtration, washed several times with water,
and recrystallized from EtOH/DMF to give the title compounds.

Iminoselenazolidines
113
5-(4-Fluorobenzyl)selenazolidin-1,4-dione (5a). m.p. 209–211◦C in
1
2
3
42% yield. H NMR ppm: δ 3.23 (dd, 1H, CH2, J 14.4, J 7.6), 3.50
(dd, 1H, CH2, 3J 4.4), 4.91 (dd, 1H, CH), 7.02–7.09 (m, 2H, C6H4), 7.23–
7.30 (m, 2H, C6H4), 11.27 (br. s, NH; exchangeable). Anal. requires
for C10H8FNO2Se (272.14) calcd./found: C, 44.14/43.90; H, 2.96/2.88;
N, 5.15/5.19.
5-(3-Chloro-4-methylbenzyl)selenazolidin-1,4-dione (5b). m.p. 202–
1
203◦C in 38% yield. H NMR ppm: δ 2.31 (s, 3H, CH3), 3.20 (dd, 1H,
2
3
3
CH2, J 14.4, J 7.6), 3.47 (dd, 1H, CH2, J 4.8), 4.92 (dd, 1H, CH),
7.09 (d, 1H, C6H3, 3J 7.6), 7.23 (d, 1H, C6H3), 7.27 (s, 1H, C6H3), 11.28
(br. s, NH; exchangeable). Anal. requires for C11H10ClNO2Se (302.62)
calcd./found: C, 43.66/43.59; H, 3.33/3.40; N, 4.63/4.56.
REFERENCES
[1] N. D. Obushak, V. S. Matiychuk, and R. Ya. Vasylyshyn, Russ. J. Org. Chem. (in
press).
[2] V. P. Litvinov and V. D. Diachenko, Russ. Chem. Rev., 66(11), 923 (1997).
[3] R. Larsen, 1,3-Selenazoles, in Comprehensive Heterocyclic Chemistry II, edited by A.
Katritzky, C. W. Rees, E. F. V. Scriven Eds. (Elsevier Science, Oxford, 1996), vol. 3,
chap. 8.
[4] D. K. Klayman and W. W. H. Gunther, eds. Organic Selenium Compounds: Their
Chemistry and Biology (Wiley, New York, 1973), p. 663.
[5] Y. Kumar, R. Green, D. S. Wise, L. L. Wotring, and L. B. Townsend, J. Med. Chem.,
36, 3843 (1993).
[6] Y. Kumar, R. Green, D. S. Wise, L. L. Wotring, and L. B. Townsend, J. Med. Chem.,
36, 3849 (1993).
[7] R. N. Hanson and M. A. Davis, J. Heterocycl. Chem., 18, 205 (1981).
[8] A. Shafiee, M. A. Ebrahimzadeh, and A. Maleki, J. Heterocycl. Chem., 36(4), 901
(1999).
[9] R. N. Hanson, J. Heterocycl. Chem., 21(1), 57 (1984).
[10] L.-L. Lai and D. H. Reid, Synthesis, 870 (1993).
[11] Bo Liu, C. Xu, and X. Zhou, Huaxue Shiji (Chem. Reagents), 15, 334 (1993);
Chem. Abstr., 121, 57594t (1994).
[12] H. M. Hassaneen, A. M. Farad, M. S. Algharib, and A. S. Shawali, Org. Prep. Proc.
Int., 20, 505 (1988).
[13] S. Bilinski, L. Bielak, J. Chmelevski, B. Marcewicz-Rojewska, and J. Musik, Acta
Pol. Pharm., 46, 219 (1989).
[14] M. F. Utinan, R. E. Valter, and G. A. Karlivan, Chem. Heterocycl. Compd., 25(10),
1201 (1989).
[15] A. M. Comrie, D. Dingwall, and J. B. Stenlake, J. Chem. Soc., 5713 (1963).
[16] M. Koketsu, Y. Takenaka, and H. Ishihara, Synthesis, 731 (2001).
[17] N. D. Obushak, V. S. Matiychuk, and N. I. Ganushchak, Russ. J. Org. Chem., 34(2),
239 (1998).
[18] B. B. Lohray, V. Bhushan, A. S. Reddy, et al., J. Med. Chem., 42, 2569 (1999).
[19] A. A. Parulkar, M. L. Pendergrass, R. Granda-Ayala, T. R. Lee, and V. A. Fonseca,
Ann. Intern. Med., 134, 61 (2001).