Synthesis of novel gold(I) complexes derived by AgCl-elimination between [AuCl(PPh3)] and silver(I) heterocyclic carboxylates, and their antimicrobial activities. Molecular structure of [Au(R,S-Hpyrrld)(PPh 3)] (H2pyrrld = 2-pyrrolidone-5-carboxylic acid)

Article abstract of DOI:10.1016/j.inoche.2006.01.001

Novel gold(I) complexes with hard (O donor) and soft (P donor) Lewis bases, [Au(R,S-Hpyrrld)(PPh₃)] ? CHCl₃ 1 (H ₂pyrrld = 2-pyrrolidone-5-carboxylic acid) and [Au(R,S-othf)(PPh ₃)] 2 (Hothf = 5-oxo-2-tetrahydrofurancarboxylic acid), were prepared by the AgCl elimination reaction in CHCl₃ between [AuCl(PPh ₃)] and the Ag-O bonding precursors such as [Ag₂(R- Hpyrrld)(S-Hpyrrld)] and [Ag₂(R-othf)(S-othf)]. Molecular structure of 1 was determined as a discrete monomer of the 2-coordinate AuOP core. In the preparation of 1 and 2, the use of the Ag-O bonding precursors is crucial. Both complexes 1 and 2 showed selective antimicrobial activities against Gram-positive bacteria and yeasts.

Full text of DOI:10.1016/j.inoche.2006.01.001

Inorganic Chemistry Communications 9 (2006) 355–359
www.elsevier.com/locate/inoche
Synthesis of novel gold(I) complexes derived by AgCl-elimination
between [AuCl(PPh3)] and silver(I) heterocyclic carboxylates, and their
antimicrobial activities. Molecular structure of
[Au(R,S-Hpyrrld)(PPh3)] (H2pyrrld = 2-pyrrolidone-5-carboxylic acid)
*
Ryusuke Noguchi, Akihiro Hara, Akiyoshi Sugie, Kenji Nomiya
Department of Materials Science, Faculty of Science, Kanagawa University, Tsuchiya, Hiratsuka, Kanagawa 259-1293, Japan
Received 17 December 2005; accepted 12 January 2006
Available online 2 March 2006
Abstract
Novel gold(I) complexes with hard (O donor) and soft (P donor) Lewis bases, [Au(R,S-Hpyrrld)(PPh3)] Æ CHCl3 1 (H2pyrrld = 2-pyr-
rolidone-5-carboxylic acid) and [Au(R,S-othf)(PPh3)] 2 (Hothf = 5-oxo-2-tetrahydrofurancarboxylic acid), were prepared by the AgCl
elimination reaction in CHCl3 between [AuCl(PPh3)] and the Ag–O bonding precursors such as [Ag2(R-Hpyrrld)(S-Hpyrrld)] and
[Ag2(R-othf)(S-othf)]. Molecular structure of 1 was determined as a discrete monomer of the 2-coordinate AuOP core. In the preparation
of 1 and 2, the use of the Ag–O bonding precursors is crucial. Both complexes 1 and 2 showed selective antimicrobial activities against
Gram-positive bacteria and yeasts.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Gold(I) complexes; Triphenylphosphine; 2-Pyrrolidone-5-carboxylic acid; 5-Oxo-2-tetrahydrofurancarboxylic acid; X-ray crystal structure;
Antimicrobial activities
There is considerable interest in the coordination chem-
istry of coinage metal (silver(I) and gold(I)) complexes with
biological and pharmacological activity. In bioinorganic
chemistry of coinage metal(I) complexes, there have been
reported various studies of gold(I) complexes related to
their antiarthritic [1–3], antitumor [2–6], anti-HIV [2,3]
and antimicrobial activities [7–12] and those of silver(I)
complexes related to their antiethylene [13–15], antimicro-
bial [16–24], antitumor [25] and antiviral activities [26,27].
The molecular design of such silver(I) and gold(I) com-
plexes is an intriguing aspect of the bioinorganic chemistry
of metal-based drugs.
clic carboxylate ligands such as H2pyrrld (H2pyrrld = (S)-
(ꢀ)- and (R)-(+)-2-pyrrolidone-5-carboxylic acid), Hothf
(Hothf = (S)-(+)- and (R)-(ꢀ)-5-oxo-2-tetrahydrofuran-
carboxylic acid), H2asp (H2asp = D- and L-aspartic acid)
and Hca (Hca = camphanic acid (C10H14O4), i.e.,
(1R,4S)- and (1S, 4R)-4,7,7-trimethyl-3-oxo-2-oxabicyclo-
[2.2.1]-heptane-1-carboxylic acid). These Ag–O bonding
complexes have shown a wide spectrum of effective antimi-
crobial activities against bacteria, yeast and molds [16–20].
On the other hand, the antimicrobial test by 2-coordi-
nate AuSP and AuNP complexes such as [Au(L)(PPh3)]
(HL = 2-mercaptopropionic acid (2-H2mpa), 6-mercap-
tonicotinic acid (6-H2mna), 2-mercaptonicotinic acid
(2-H2mna), D-penicillamine (D-H2pen), D,L-penicillamine
(D,L-H2pen), 2-mercaptobenzoic acid (2-H2mba), 3-merca-
ptobenzoic acid (3-H2mba), 4-mercaptobenzoic acid (4-
H2mba), imidazole (Him), pyrazole (Hpz), 1,2,3-triazole
(1,2,3-Htriz), 1,2,4-triazole (1,2,4-Htriz), tetrazole (Htetz))
has shown selective and effective activities against two
Recently, we have prepared several water-soluble,
light-stable chiral silver(I) carboxylates {[Ag(Hpyrrld)]2}n
[16,17], {[Ag(othf)]2}n [18], {[Ag(Hasp)]2}n [19], {[Ag2
(ca)2]}n and {[Ag2(ca)2(Hca)2]}n [20] using chiral heterocyl-
*
Corresponding author. Tel.: +81 463 59 4111; fax: +91 463 58 9684.
E-mail address: nomiya@chem.kanagawa-u.ac.jp (K. Nomiya).
1387-7003/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2006.01.001

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R. Noguchi et al. / Inorganic Chemistry Communications 9 (2006) 355–359
Gram-positive bacteria (Bacillus subtilis, Staphylococcus
aureus) and modest activities against one or two yeasts
(Candidae albicans) [11,12]. Thus, we have aimed at synthe-
sizing novel PPh3-gold(I) complexes with O-donor ligands
such as Hpyrrldꢀ and othfꢀ in order to examine if the
AuOP-core complexes show selective and effective activities
against Gram-positive bacteria and yeasts. There have been
reported only a few examples of the 2-coordinate AuOP
complexes by Jones’s group, e.g., [Au(C2H3O2)(PPh3)]
(C2H3O2 = acetate) [28], [Au(C7H5O2)(PPh3)] (C7H5O2
instance, the reactions among [AuCl(PPh3)], NaOH and
HL (HL = R,S-H2pyrrld, R,S-Hothf) did not give the tar-
get compounds 1 and 2.
The presence of one solvated CHCl3 molecule in 1 was
confirmed by elemental analysis, weight loss observed in
TG/DTA measurement and, also, X-ray crystallography.
Complex 2 was obtained without any solvent molecules.
FTIR spectra of 1 and 2 confirmed the presence of coordi-
nated PPh3 molecules as typical, intense vibrational bands.
The 31P NMR spectra in CDCl3 of 1 and 2 showed only
one resonance at around d 28.0, the chemical shift of which
can be compared with the signal at d 29.4 of the related
= benzoate)
[29],
[Au(O2C-CH2NHC(O)Ph)(PPh3)]
(O2CCH2NHC(O)Ph = hippurate) [30].
In this work, we have examined the AgCl elimination
reaction in CHCl3 between [AuCl(PPh3)] [31] and the
Ag–O bonding precursor ([Ag(Hpyrrld)]2 [16,17] or
[Ag(othf)]2 [18]) and obtained two light-stable, novel
gold(I) complexes with hard (O donor) and soft (P donor)
Lewis bases, i.e., [Au(R,S-Hpyrrld)(PPh3)] Æ CHCl3 1 [32]
and [Au(R,S-othf)(PPh3)] 2 [33]. These complexes were
characterized with elemental analysis, TG/DTA, FTIR,
solution (1H, 13C, 31P) NMR and X-ray crystallography.
Their antimicrobial activities against selected bacteria,
yeast and molds were also tested.
AuOP complex, [Au(O2CNEt2)(PPh3)] ðO2CNEtꢀ ¼ N;
2
N0-diethylcarbamatoÞ [34].
1
The H NMR spectra in CDCl3 of 1 and 2 showed sig-
nals of the coordinating heterocyclic ligands consisting of
multiplet peaks for the two methylene groups (H4 and
H3) and double doublet peaks (four lines) for the H5 pro-
ton within the ring, as well as a single peak for NH proton
for 1, in addition to signals of the coordinating PPh3
ligand. The 13C NMR spectra in CDCl3 of 1 and 2 showed
the (C4, C3, C5, C6 and C2) signals for the coordinating
Hpyrrldꢀ and othfꢀ ligands, respectively.
Herein we report the synthesis and characterization of 1
and 2, including the crystal and molecular structures of 1,
and their antimicrobial activities.
X-ray structure analysis of 1 revealed the almost linear
2-coordinate gold(I) complex with AuOP core with
Hpyrrldꢀ and PPh3 ligands (Au1–O3 2.072(3), Au1–P1
˚
2.2137(16) A, O3-Au1-P1 176.61(10)ꢁ) (Fig. 1) [35]. Com-
plex 1 was a discrete monomer without any intermolecular
interaction. The coordinating oxygen atom was based on
the carboxyl oxygen, but not the carbonyl oxygen. The sol-
vated CHCl3 molecule was found in the crystal structure,
although it was highly disordered. In the unit cell, a com-
bination of two R-forms and two S-forms (Z = 4), i.e., a
racemic mixture, was found.
3
4
3
4
5
2
H
5
2
H
O
COOH
6
N
H
O
COOH
6
O
2-pyrrolidone-5-carboxylic acid
(H2pyrrld)
5-oxo-2-tetrahydrofurancarboxylic acid
(Hothf)
The bond distances and angles of the AuOP core in 1
can be compared with those of a couple of examples of
neutral 2-coordinate O–Au(I)–P complexes such as
The molecular formulas of 1 and 2 were consistent with
all data of elemental analysis, TG/DTA, FTIR, solution
(1H, 13C, 31P) NMR spectra and, also, X-ray structure
analysis. Complex 1 was synthesized by reaction of the
dimeric silver(I) carboxylate precursor [Ag(Hpyrrld)]2 with
the gold(I) precursor [AuCl(PPh3)] in CHCl3 [32]. Colorless
crystals of 1 soluble in most organic solvents were obtained
in 67.9% (0.24 g) yield by a vapor diffusion with CHCl3/
light petroleum system as the internal/external solvents.
Complex 2 as a colorless crystalline compound soluble in
most organic solvents was obtained in 59.5% (0.35 g) yield
by reaction of [Ag(othf)]2 with [AuCl(PPh3)] in CHCl3 [33].
Synthetic reactions of 1 and 2, both based on AgCl elim-
ination between the two precursors, are shown as follows:
½Ag2ðR-HpyrrldÞðS-HpyrrldÞꢁ þ 2½AuClðPPh3Þꢁ
! 2½AuðR; S-HpyrrldÞðPPh3Þꢁ1 þ 2AgCl
½Ag2ðR-othfÞðS-othfÞꢁ þ 2½AuClðPPh3Þꢁ
! 2½AuðR; S-othfÞðPPh3Þꢁ2 þ 2AgCl
Fig. 1. Molecular structure of [Au(R,S-Hpyrrld)(PPh3)] Æ CHCl3 1 with
In the preparation of 1 and 2, the use of the Ag–O bond-
ing precursor [Ag(Hpyrrld)]2 or [Ag(othf)]2 is crucial. For
˚
50% probability ellipsoids. Selected interatomic distances (A) and angles
˚
(ꢁ): Ag1-O3 2.072(3), Au-P1 2.2137(16) A; O3-Au1-P1 176.61(10)ꢁ.

R. Noguchi et al. / Inorganic Chemistry Communications 9 (2006) 355–359
357
˚
[Au(C2H3O2)(PPh3)] (Au–O 2.063(6), Au–P 2.207(3) A, O–
Au–P 177.3(2)ꢁ) [28], [Au(C7H5O2)(PPh3)] (Au–O 2.033(6),
˚
Au–P 2.213(3) A, O–Au–P 173.7(2)ꢁ) [29], [Au(O2CCH2
˚
NHC(O)Ph)(PPh3)] (Au–O 2.077(5), Au–P 2.212(2) A,
O–Au–P 174.6(1)ꢁ) [30].
Antimicrobial activities, estimated by minimum inhibi-
tory concentration (MIC; lg mlꢀ1), of the 2-coordinate
gold(I)–PPh3 complexes with AuOP cores 1 and 2 are
shown in Table 1, together with the prototypical results
of the previously reported complexes [Au(D-Hpen)(PPh3)],
[Au(D,L-Hpen)(PPh3)] Æ 0.5MeOH
and
[Au(4-Hmba)
(PPh3)] Æ 0.3(acetone) with AuSP core [12] and [Au(1,2,3-
triz)(PPh3)] with AuNP core [11], and free R,S-H2pyrrld
and S-Hothf ligands. All of these complexes were water
insoluble, and the antimicrobial test was carried out in a
suspension of aqueous media.
As for several phosphinegold(I) complexes with N–Au–P
and S–Au–P cores, regardless of whether in a homogeneous
organic system or a heterogeneous aqueous suspension, the
common activities have been observed, i.e., selective antimi-
crobial activities against two Gram-positive bacteria (B.
subtilis, S. aureus) and modest activities against one or
two yeasts (C. albicans) [11,12], which were well correlated
with their ligand-exchangeability, i.e. with the identity of
the complex.
Complex 2 showed selective and effective activities
against two Gram-positive bacteria (B. subtilis, S. aureus)
and modest activities against two yeasts (C. albicans, S.
cerevisiae), but it showed no activity against Gram-nega-
tive bacteria (Escherichia coli, Pseudomonas aeruginosa)
and molds (Aspergillus niger, P. citrinum). Complex 1
showed modest activities against only one Gram-positive
bacterium (S. aureus) and poor activities against two yeasts
(C. albicans, S. cerevisiae). These antimicrobial activities
and the spectra are essentially consistent with the previous
results [11,12]. Thus, we can conclusively propose that the
observed antimicrobial activities are commonly observed
for the 2-coordinate gold(I)-PPh3 complexes with AuOP,
AuSP and AuNP cores. The subtly different activities
between 1 and 2 may come from the presence of solvated
CHCl3 molecule in 1. In fact, the separately prepared, fresh
powder sample without any solvated molecules [Au(R,S-
Hpyrld)(PPh3)] (1a) showed the effective activities against
two Gram-negative bacteria (E. coli, P. aeruginosa) and
modest activities against two yeasts (C. albicans, S. cerevi-
siae) as commonly observed in other phosphinegold(I)
complexes without solvated molecules. Also, relating to
these facts, the previously reported gold(I) complexes with
solvated molecules, e.g., [Au(D,L-Hpen)(PPh3)] Æ 0.5MeOH
[12] and [Au(4-Hmba)(PPh3)] Æ 0.3(acetone) [12], have
shown modest activities against only one Gram-positive
bacterium (S. aureus).1
1
In Table 7 in Ref. [12] the antimicrobial activities by [Au(4-
Hmba)(PPh3)] Æ 0.3(acetone) have been erroneously described as MIC
125 for B. subtilis, which should be corrected as MIC 125 for S. aureus.

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R. Noguchi et al. / Inorganic Chemistry Communications 9 (2006) 355–359
[23] A. Melaiye, Z. Sun, K. Hindi, A. Milsted, D. Ely, D.H. Reneker, C.A.
In summary, two novel gold(I) complexes with hard (O
Tessier, W.J. Youngs, J. Am. Chem. Soc. 127 (2005) 2285.
[24] M.A.A. O’Neill, G.J. Vine, A.E. Beezer, A.H. Bishop, J. Hadgraft, C.
Labetoulle, M. Chloe, P.G. Bowler, Int. J. Pharm. 270 (2004) 323.
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Nayal, D. Egan, C. Deegan, G.J. Finn, J. Inorg. Biochem. 98 (2004)
1361.
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Michaelides, J. Balzarini, E.D. Clercq, Eur. J. Inorg. Chem. 7 (2004)
1420.
donor) and soft (P donor) Lewis bases, 1 and 2, were syn-
thesized from the water-soluble, light-stable silver(I)–oxy-
gen bonding precursors and their selective antimicrobial
activities against selected Gram-positive bacteria and
yeasts were confirmed. The antimicrobial results were con-
sistent with the previously reported results [11,12]. The
crystal and molecular structures of 1 were successfully
determined. The present gold(I) complexes are labile and
will probably be precursors for other gold(I) complexes.
[27] P.C. Zachariadis, S.K. Hadjikakou, N. Hadjiliadis, A. Michaelides, S.
Skoulika, Y. Ming, Y. Xiaolin, Inorg. Chim. Acta 343 (2003) 361.
[28] P.G. Jones, Acta Crystallogr. C40 (1984) 1320.
[29] P.G. Jones, Acta Crystallogr. C41 (1985) 905.
Acknowledgement
[30] P.G. Jones, R. Schelbach, J. Chem. Soc., Chem. Commun. (1988)
1338.
[31] M.I. Bruce, B.K. Nicholson, O.B. Shawkataly, Inorg. Synth. 26
(1986) 324.
This work was supported by a High-tech Research Cen-
ter Project from the Ministry of Education, Culture,
Sports, Science and Technology, Japan.
[32] [Au(R,S-Hpyrrld)(PPh3)] Æ CHCl3 1: To the solution of 0.247 g
(0.50 mmol) of the gold(I) precursor [AuCl(PPh3)] dissolved in
30 mL CHCl3 was added 0.472 g (1.00 mmol) of the meso-form of
silver(I) complex [Ag2(R-Hpyrrld)(S-Hpyrrld)]. After stirring for one
day, white–violet powder of AgCl produced was filtered off through a
membrane filter (JV 0.1 lm). The colorless clear filtrate was evapo-
rated to dryness with a rotary evaporator at 30 ꢁC. The residue was
dissolved in 10 mL CHCl3, followed by filtering through a folded filter
paper (Whatman #5). The clear filtrate was added dropwise to
200 mL light petroleum. A white precipitate was collected on a
membrane filter (JV 0.1 lm), washed with light petroleum (50 mL · 2)
and dried in vacuo for 2 h. The white powder was redissolved in 20
mL CHCl3 and the solution was passed thorough a folded filter paper
(Whatman #5). Vapor diffusion at 10 ꢁC was performed using the
filtrate as an inner solution and 100 mL light petroleum as an outer
solvent. After ten days, colorless needle crystals deposited, which were
collected on membrane filter (JV 0.1 lm), washed with light petro-
leum (50 mL · 2), thoroughly dried by suction and dried in vacuo for
2 h. Colorless needle crystals, obtained in 67.9% (0.24 g scale) yield,
were soluble in most organic solvents and insoluble in water, light
petroleum, Et2O and hexane. Found: C, 40.84; H, 3.02; N, 1.98. Calc.
for C24H22NCl3PO3Au or [Au(Hpyrrld)(PPh3)] Æ CHCl3: C, 40.79; H,
3.14; N, 1.98%. TG/DTA data: weight loss of 14.5% was observed
below 152 ꢁC (calc. for 1.0 CHCl3, 16.9%). Decomposition began
around 136 ꢁC with endothermic peaks at 112, 274 ꢁC and exothermic
peaks at 166, 345 ꢁC. Prominent IR bands in the 1700–400 cmꢀ1
region (KBr disk): 1676vs, 1589vs, 1478m (PPh3), 1434s (PPh3),
1408s, 1298s, 1179w, 1101s (PPh3), 1026w, 998w, 747vs (PPh3), 713s
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.inoche.2006.
01.001.
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(PPh3), 692vs (PPh3), 545vs (PPh3), 500vs (PPh3) cmꢀ1 1H NMR
.
(CDCl3, 23.9 ꢁC): d 2.32–2.50 (4H, m, H3 and H4), 4.25 (1H, dd, H5),
5.95 (1H, s, NH), 7.48–7.56 (15H, m, Aryl). 13C NMR (CDCl3,
25.1 ꢁC): d 26.7 (C4), 27.5 (C3), 79.1 (C5), 128.1 (d, JCP 65.5 Hz, Ph),
129.1 (d, JCP 12.4 Hz, Ph), 131.9 (d, JCP 2.5 Hz, Ph), 134.0 (d, JCP
14.1 Hz, Ph), 174.4 (C6), 177.1 (C2). 31P NMR (CDCl3, 24.1 ꢁC): d
28.0. The separately prepared, chiral complexes [Au(R-
Hpyrrld)(PPh3)] and [Au(S-Hpyrrld)(PPh3)], were difficult to crystal-
lize by vapor diffusion of the inner CHCl3 solution with the outer
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crystallization, was also used for the antimicrobial test.
[33] [Au(R,S-othf)(PPh3)] 2: Complex 2 was prepared by a 1:2 molar-ratio
reaction in 60 mL of CHCl3 of [Ag2(R-othf)(S-othf)] (0.948 g,
2.00 mmol) with [AuCl(PPh3)] (0.495 g, 1.00 mmol). By a similar
work-up to synthesis of 1, a colorless powder of 2 was obtained in
59.5% (0.35 g scale) yield, which was soluble in most organic solvents
and insoluble in water, Et2O, hexane and light petroleum. Found: C,
46.90; H, 3.29. Calc. for C23H20O4PAu or [Au(othf)(PPh3)]: C, 46.95;
H, 3.43%. TG/DTA data: no weight loss was observed before
decomposition. Decomposition began around 166 ꢁC with an endo-
thermic peak at 184 ꢁC and exothermic peaks at 200, 263 ꢁC.

R. Noguchi et al. / Inorganic Chemistry Communications 9 (2006) 355–359
359
Prominent IR bands in the 1800–400 cmꢀ1 region (KBr disk): 1780vs,
1652vs, 1624m, 1437s (PPh3), 1379m, 1281m, 1253s, 1180m, 1154s,
1102s (PPh3), 1056m, 1039m, 998m, 754s (PPh3), 712s (PPh3), 693vs
(PPh3), 545vs (PPh3), 509vs (PPh3) cmꢀ1. 1H NMR (CDCl3, 24.5 ꢁC):
d 2.40–2.70 (4H, m, H3 and H4), 4.98 (1H, dd, H5), 7.48–7.56 (15H,
m, Aryl). 13C NMR (CDCl3, 25.1 ꢁC): d 26.7 (C4), 27.5 (C3), 79.1
(C5), 128.1 (d, JCP 65.5 Hz, Ph), 129.1 (d, JCP 12.4 Hz, Ph), 131.9 (d,
JCP 2.5 Hz, Ph), 134.0 (d, JCP 14.1 Hz, Ph), 174.4 (C6), 177.1 (C2).
31P NMR (CDCl3, 24.6 ꢁC): d 28.1. Complex 2 was crystallized by
vapor diffusion of the inner CHCl3 solution with the outer solvent
hexane in a refrigerator at 4 ꢁC, but the crystals were not suitable for
X-ray diffraction measurements. The separately prepared, chiral
complexes [Au(R-othf)(PPh3)] and [Au(S-othf)(PPh3)], were not
crystallized, but oiled.
[34] R. Alessio, D.B. Dell’Amico, F. Calderazzo, U. Englert, A. Guarini,
L. Labella, P. Strasser, Helv. Chim. Acta 81 (1998) 219.
[35] The intensity data were collected at 90 K on a Bruker SMART/APEX
CCD diffractometer. The structure was solved by direct methods
(SHELXTL version 5.10), and refined by a full-matrix least-squares
on F2. Crystal data for 1: C23H21AuNO3P Æ CHCl3; M = 706.74,
monoclinic, space group P21/n, a = 9.092(7), b = 27.68(2),
3
˚
˚
c = 10.628(8) A, b = 107.818(12)ꢁ, V = 2546(3) A , Z = 4, Dc =
1.844 g cmꢀ3, l(Mo Ka) = 6.182 mmꢀ1. R1 = 0.0519, wR2 = 0.1022
(for all data). Rint = 0.0545, R1 = 0.0392, wR2 = 0.0965, GOF =
1.087 (6180 total reflections, 4909 unique reflections where I > 2r(I)).
The details of the crystal data have been deposited with Cambridge
Crystallographic Data Centre as supplementary publication no.
CCDC 259302 for 1.