Syntheses of the first Se-nitrososelenol and related compounds

Article abstract of DOI:10.1080/10426500590906508

The first stable Se-nitrososelenol (RSeNO) and selenonitrate (RSeNO ₂) were synthesized by taking advantage of bowl-type steric protection groups, and their spectral properties and reactivities were elucidated. X-ray crystallographic analysis e

Full text of DOI:10.1080/10426500590906508

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Syntheses of the First Se-
Nitrososelenol and Related
Compounds
Kei Goto a , Keiichi Shimada a & Takayuki Kawashima
a
a Department of Chemistry, Graduate School of
Science, The University of Tokyo, 7-3-1 Hongo ,
Bunkyo-ku, Tokyo, 113-0033, Japan
Published online: 01 Feb 2007.
To cite this article: Kei Goto , Keiichi Shimada & Takayuki Kawashima
(2005) Syntheses of the First Se-Nitrososelenol and Related Compounds,
Phosphorus, Sulfur, and Silicon and the Related Elements, 180:3-4, 945-949, DOI:
10.1080/10426500590906508
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Phosphorus, Sulfur, and Silicon, 180:945–949, 2005
Copyright © Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500590906508
Syntheses of the First Se-Nitrososelenol and Related
Compounds
Kei Goto
Keiichi Shimada
Takayuki Kawashima
Department of Chemistry, Graduate School of Science, The University
of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
The first stable Se-nitrososelenol (RSeNO) and selenonitrate (RSeNO ) were synthe-
2
sized by taking advantage of bowl-type steric protection groups, and their spectral
properties and reactivities were elucidated. X-ray crystallographic analysis estab-
lished their structures.
Keywords Bowl-type molecule; Se-nitrososelenol; selenonitrate; steric protection
INTRODUCTION
S-Nitrosothiols (RSNO) have been attracting increasing attention in
view of their role as potential biocatalysts and reagents for the stor-
age and transport of nitric oxide (NO) in vivo1,2 although the eluci-
dation of their properties has often been hampered by their inherent
instability. Thionitrates (RSNO2) have also been recognized as impor-
tant species from the viewpoints of their physiological activity and
synthetic utility.3,4 Whereas Se-nitrososelenols (RSeNO) and selenoni-
trates (RSeNO2) are very intriguing species as the selenium analogues
of S-nitrosothiols and thionitrates, there has been no report on their
synthesis. Previously we reported the synthesis and isolation of the sta-
ble S-nitrosothiols and thionitrates bearing bowl-type substituents.5,6
Received January 20, 2004; accepted September 29, 2004.
This work was partly supported by Grants-in-Aid for The 21st Century COE Program
for Frontiers in Fundamental Chemistry (Takayuki Kawashima) and for Scientific Re-
search (Nos. 12042220, 14703066 (K.G.), and 15105001 (Takayuki Kawashima) from the
Ministry of Education, Culture, Sports, Science and Technology, Japan. We also thank
Tosoh Finechem Corporation for the generous gifts of alkyllithiums.
Address correspondence to Kei Goto, The University of Tokyo, Department of Chem-
istry, Graduate School of Science, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
E-mail: goto@chem.s.u-tokyo.ac.jp
945

946
K. Goto et al.
FIGURE 1 Structure of 1.
Here we report the syntheses of the first stable Se-nitrososelenol and
selenonitrate by taking advantage of bowl-type steric protection groups.
RESULTS AND DISCUSSION
Because the selenium-nitrogen bond of the Se-NO functionality is con-
sidered to be weaker than the sulfur-nitrogen bond of the S-NO func-
tionality, Se-nitrososelenols are supposed to be more labile than S-
nitrosothiols. However, we previously reported that S-nitrosothiols can
have a long life time if their bimolecular decomposition is sterically
suppressed by bowl-type substituents.5,6 This methodology is expected
also to be effective for stabilization of Se-nitrososelenols. We previously
reported the synthesis of a stable selenenic acid (RSeOH) by taking
advantage of the bowl-type steric protection group 1 (denoted as Bmt)
(Figure 1) and demonstrated three processes included in the catalytic
cycle of glutathione peroxidase experimentally.7 We first examined the
nitrosation of selenol 2 bearing the Bmt group. When selenol 2 was
treated with tert-butyl nitrite, quantitative formation of the correspond-
ing Se-nitrososelenol 3 was observed (Scheme 1). In 77Se NMR (CDCl3),
SCHEME 1
3 showed a signal at δ 2125, an extremely low-field for organoselenium
compounds. Although Se-nitrososelenol 3 was relatively stable in solu-
tion, 3 was gradually converted to diselenide 4 at room temperature.
Removal of the solvent from the solution containing 3 afforded a mixture
of 3 and 4, and it was difficult to isolate 3 as pure specimen. Okazaki
and coworkers reported that an S-nitrosothiol bearing the same sub-
stituent, BmtSNO, is stable at room temperature and that heating in

Syntheses of the First Se-Nitrososelenol Compounds
947
refluxing benzene is necessary for its conversion to the corresponding
disulfide, BmtSSBmt.8 These results demonstrate that bimolecular de-
composition of an Se-nitrososelenol is much easier than that of an S-
nitrosothiol.
When an excess amount of 1-butanethiol was added to a solution of
Se-nitrososelenol 3, the corresponding selenenyl sulfide 5 was obtained
quantitatively (Scheme 2). Air oxidation of 3 afforded the corresponding
selenonitrate 6 quantitatively, which was isolated as stable colorless
crystals. This is the first example of a stable selenium analogue of or-
ganic nitrates. The 77Se NMR (CDCl3) spectrum of 6 showed a sig-
nal at δ 1437. In the IR spectrum, bands at 1529 and 1284 cm−1 were
SCHEME 2
FIGURE 2 ORTEP drawing of 6 (50% probability).

948
K. Goto et al.
FIGURE 3
observed, which correspond to the asymmetric and symmetric stretch-
ing of NO2, respectively. The structure of 6 was established by X-ray
crystallographic analysis (Figure 2). For a selenonitrate, there are two
other possible tautomeric forms, a selenenyl nitrite form (R-Se-O-NO)
and a seleninyl nitrite form (R-Se(O)-NO). The present results clearly
indicate that 6 has a selenonitrate form (R-Se-NO2). Selenonitrate 6
easily reacted with 1-butanethiol to produce selenenyl sulfide 5.
Recently, we designed a novel bowl-type substituent 7 (Figure 3) (de-
noted as Bpq),9 which can prevent dimerization of reactive species more
effectively than the Bmt group, and applied it to the stabilization of an
S-nitrosothiol.6 Because the isolation of a stable Se-nitrososelenol was
difficult by using the Bmt group, the use of the Bpq group was examined
In the reaction of selenol 8 bearing the Bpq group with ethyl nitrite, the
corresponding Se-nitrososelenol 9 quantitatively was formed and iso-
lated as stable purple crystals (Scheme 3). This is the first example of a
SCHEME 3
stable Se-nitrososelenol. In the 77Se NMR spectrum (CDCl3), 9 showed
a signal at δ 2229. The IR spectrum of 9 showed the N–O stretching band

Syntheses of the First Se-Nitrososelenol Compounds
949
FIGURE 4 ORTEP drawing of 9 (50% probability).
at 1564 cm−1. X-ray crystallographic analysis established the structure
of 9 (Figure 4), where the C Se N O linkage adopts syn conformation
6
˚
similar to BpqSNO. The Se–N bond length [2.075(4) A] and N–O bond
˚
length [1.173(5) A] are consistent with a selenium–nitrogen single bond
and a nitrogen–oxygen double bond. Se-Nitrososelenol 9 was found to
be stable in solution at room temperature although it was converted to
diselenide 10 by heating in benzene at 80◦C. The reaction of 9 with 1-
butanethiol afforded selenenyl sulfide 11 quantitatively, indicating that
the intrinsic reactivity of the SeNO functionality with an appropriate
molecule is retained despite effective steric protection by the Bpq group.
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