Synthesis of a new chiral polyamine template - Towards an active site analogue of vanadium haloperoxidase

Article abstract of DOI:10.1055/s-1999-2969

The synthesis of a new polyamine template 1 carrying two guanidinium subunits and an imdazole ligand suitable for the recognition of vanadate is described.

Full text of DOI:10.1055/s-1999-2969

LETTER
1875
Synthesis of a New Chiral Polyamine Template – Towards an Active Site
Analogue of Vanadium Haloperoxidase
Jose Antonio Martinez-Perez, Marco Andreas Pickel, Eva Caroff, Wolf-D. Woggon*
Institut für Organische Chemie der Universität Basel, St. Johanns-Ring 19, CH-4056 Basel, Switzerland
Fax +41 61 267 11 02; E-mail: woggon@ubaclu.unibas.ch
Received 12 September 1999
Molecular modeling8 revealed that the preferred confor-
mation of the diamino azalactam 1 has both guanidinium
subunits in axial positions, facilitating, in the protonated
form, the binding of vanadate via hydrogen bridges. The
required apical imidazole replacing His496 is attached to
the secondary ring nitrogen by a short alkyl chain. A con-
venient route towards 1 proceeds via cyclization of 1,2-di-
acylhydrazides 3 (easily accessible from 2) → 4, followed
by selective reduction → 5 and subsequent reductive N-N
bond scission → 6, (Scheme 1). The key step of this syn-
thesis is the selective monoreduction of the tetrasubstitut-
ed diacylhydrazide 4. This reduction has no precedent but
the reported low yield obtained by the reaction of hy-
drazides with excess of diborane at room temperature.9
Abstract: The synthesis of a new polyamine template 1 carrying
two guanidinium subunits and an imdazole ligand suitable for the
recognition of vanadate is described.
Key words: enzymatic halogenation, lactams, polyamines, vanadi-
um haloperoxidases
Vanadium haloperoxidases are found in marine algae and
lichens catalyzing the formation of a number of haloge-
nated organic compounds that have biocidal effects and
thus often serve as chemical defense of the organism.1 The
X-ray crystal structure of VCPO from the fungus Curvu-
laria inaequalis has been recently resolved,2 revealing a
trigonal bipyramidal coordination of V5+ (Figure 1). Actu-
-
ally the VO4 group is embedded into a network of H-
bonds with amino acid residues of the protein, and two
histidines are of particular significance:3,4 His496 is coordi-
nating directly to the vanadium in an apical position,
whereas His404 which is in close proximity to the apical,
vanadium–bound oxygen may act as an acid base catalyst.
Several functional mimics of vanadium haloperoxidases
have been reported.5 It has been, however, impossible to
understand the catalytic cycle of these enzymes complete-
ly, i.e. the sequence of events such as binding of hydrogen
peroxide, oxidation of chloride, and substrate chlorina-
tion, all occuring apparently without changing the oxida-
tion state of vanadium.6 We wish to report here the
synthesis of a template suitable to bind vanadate which
was designed according to the spatial arrangement known
from the X-ray crystal structure,2 and taking into account
the well established recognition of phosphate, structurally
related to vanadate, by bisguanidinium receptors.7
a) 0.5eq NH2-NH2, DCC, N-hydroxysuccinimide, 65%; b) PPh3,
CCl4, Et3N, DMF, 68%; c) BH3, THF, 27h, Boc2O, 55%;
d) Raney Ni, i-PrOH, 92%.
Scheme 1
The preparation of a 1,2-diacylhydrazide from racemic N-
protected serine has been reported.10 The coupling of N-
Boc-L-serine 2 with hydrazine in the presence of DCC and
N-hydroxysuccinimide11 occurs without epimerization to
yield 3 (Scheme 1). Diazabicyclooctanones have been
synthesized by cyclization of 1,2-diacylhydrazides of β-
halopropionic acids in the presence of a base.12 We have
prepared the corresponding chloride of 313 which cyclizes
in situ under mild conditions to give 4. The reduction of 4
in the presence of borane (2.2 equivalents) takes place to
Ligand 1 was designed to mimic the structural properties of the active
site of vanadiumhaloperoxidase (left).
Figure 1
Synlett 1999, No. 12, 1875–1878 ISSN 0936-5214 © Thieme Stuttgart · New York

1876
J. A. Martinez-Perez et al.
LETTER
give the desired monoreduced product 5.14 After quench- Condensation of 10 and 6 to the enamine followed by re-
ing of the borane the addition of di-tert-butyldicarbonate duction with sodium cyanoborohydride under slightly
was required, because the N-protecting groups were not acidic conditions afforded the fully protected amine 12 in
completely stable under the reaction conditions. To im- a good yield (Scheme 4). To prevent the cleavage of the
prove the yield of the monoreduction 14 different reduc- trityl group the Boc protecting groups were removed at
ing agents/reaction conditions were investigated however 0 °C with HCl in dioxane to yield 13 which was used
unsuccessfully. When the reduction of 5 was carried out without further purification. For attaching the two re-
in EtOH the N-ethyl azalactam 7 was obtained.15,16
quired guanidinium groups to 13 we first employed N,N‘-
bis(tert-butoxycarbonyl)thiourea, and Mukaiyama‘s re-
agent.28 We found, however, that EDC (1-(3-dimethyl-
aminopropyl)-3-ethylcarbodiimide hydrochloride) gave
reproducibly better yields of 14. Deprotection of 14 was
carried out under acidic conditions and the resulting
polyamine 1 was purified as its picrate which was crystal-
lized several times and finally passed through an ion ex-
change column to afford pure 1 as the hydrochloride,29
1
which was characterized by H NMR (COSY, TOCSY,
ROESY), and 13C NMR-spectroscopy.
a) Raney Ni, EtOH, 73%; b) HCl•dioxane, THF/CH3OH (2:1), 97%;
c) 4,5-dihydro-1H-imidazolium-2-sulfonate, Et3N, DMF, 77%.
Scheme 2
Deprotection of 7 under standard conditions gave the pure
diamine 8, as the hydrochloride, which can be used direct-
ly for the guanidinium functionalization17,18 to furnish 9
(Scheme 2).
a) 10, CHCl3:EtOH (3:1), then NaBH3CN, AcOH, 85%; b) 4 M HCl
in dioxane, CH2Cl2; c) N,N’-Bis(tert-butoxycarbonyl)thiourea, 1-(3-
dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, THF,
44% for b) and c); d) 4M HCl in dioxane, H2O, 44%.
To provide the ethyl-imidazole appendix to the ring nitro-
gen of the azalactam 6 the imidazolyl aldehyde 10 was
prepared using metallation of the N-protected-2-methyl-
imidazole 11 under carefully selected conditions to pre-
vent alkylation of C-519 (Scheme 3). In principle this can
be accomplished by lithium complexation20 using N-
ethoxymethyl- or, as shown here, by N-trityl protection.21
Several 1-carbon electrophiles such as CO2, Eschen-
moser’s salt,22 dichloromethane, formic acid,23 DMF,24
paraformaldehyde, ethyl chloroformate or methyl
cyanoformate25 were investigated but the most effective
electrophile was found to be ethyl formate. The resulting
aldehyde 1026 is relatively unstable on silica gel and was
therefore, without further purification, directly submitted
to the Leuckart-Wallach reaction27 with 6.
Scheme 4
References and Notes
(1) Vilter, H.; Phytochemistry 1984, 23, 1387-1390. de Boer, E.;
van Kooyk, Y.; Tromp, M. G. M.; Plat, H.; Wever, R.
Biochim. Biophys. Acta 1986, 869, 48-53.
(2) Messerschmidt, A.; Wever, R. Proc. Natl. Acad. Sci. USA
1996, 93, 392-396.
(3) Fukui, K.; Ohya-Nishiguchi, H.; Kamada, H. Inorg. Chem.
1998, 37, 2326-2327.
(4) Messerschmidt, A.; Prade, L.; Wever, R. Biol. Chem. 1997,
378, 309.
(5) Colpas, G. J.; Hamstra, B. J.; Kempf, J. W.; Pecoraro, V. L. J.
Am. Chem. Soc. 1996, 118, 3469. Hamstra, B. J.; Colpas, G.
J.; Pecoraro, V. L. Inorg. Chem. 1998, 37, 949.
(6) For a current review on mechanistic considerations see:
Butler, A. Coord. Chem. Rev. 1999, 187, 17-35.
(7) Dietrich, B.; Fyles, D. L.; Fyles, T. M.; Lehn, J. M. Helv.
Chim. Acta 1979, 62, 2763-2787. Muche, M-S.; Göbel, M. W.
Angew. Chem. Int. Ed. Engl. 1996, 35, 2126-2129. Perreault,
D. M.; Chen, X.; Anslyn, E. V. Tetrahedron 1995, 51, 353-
362.
a) ClCPh3, Et3N, DMF, 95%; b) nBuLi, THF, HCOOEt, 5% citric
acid aq soln, 80%.
(8) Gerber, P. R.; Müller, K. J. Compt. Aided Mol. Design 1995,
9, 251-268. Gerber, P. R.; Gubernator, K.; Müller, K. Helv.
Chim. Acta 1988, 71, 1429-1441.
Scheme 3
(9) Feuer, H.; Brown, Jr., F. J. Org. Chem. 1970, 35, 1468-1471.
(10) Gansser, C. Bull. Soc. Chim. Fr. 1966, 1713-1714.
Synlett 1999, No. 12, 1875–1878 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Synthesis of a New Chiral Polyamine Template
1877
(11) Benoiton, N. L.; Kuroda, K.; Chen, F. M. F. Int. J. Peptide
Protein Res. 1980, 15, 475-479. Wünsch, E.; Drees, F. Chem.
Ber. 1966, 99, 110-120.
(12) Bellasio, E.; Gallo, G. Farmaco, Ed. Sci. 1970, 25, 295-304;
Chem. Abstr. 1970, 72, 132598. Bellasio, E.; Pagani, G.;
Ripamonti, A.; Testa, E. Farmaco, Ed. Sci. 1965, 20, 428-445;
Chem. Abstr. 1965, 63, 9945.
(13) Appel, R. Angew. Chem. Int. Ed. Engl. 1975, 14, 801-812.
(14) Procedure for the preparation of 3S,7R-bis-[(tert-
butoxycarbonyl)amino]-2-keto-1,5-diazabicyclo[3.3.0]octane
(5): To an ice cooled solution of 4 (1.0g, 2.7 mmol) in dry THF
(10mL) a solution of BH3 in THF (1M, 7.6mL) was slowly
added. The resulting mixture was stirred at r.t. for 16h and
cooled to 0 °C before the addition of MeOH (4mL) and HCl
in dioxane (4M, 2.5mL). After stirring for 7h at r.t. and
cooling with an ice bath, a solution of Na2CO3 (2M, 2mL) and
di-tert-butyldicarbonate (1.25g, 5.7mmol) were successively
added. To the resulting mixture a solution of Na2CO3 (2M,
8.0mL) was slowly added. The resulting suspension was
stirred at r.t. overnight, filtered and the filtrate was
H2O 1:1) to afford 9, (310mg, 77%).1H NMR (H2O/10% D2O,
ppm, d):8.21 (d, 1H, J = 6.1 Hz), 4.54 (dd, 1H, J = 10.5 and
2.9 Hz), 3.76, 3.74 (2s+m, 9H), 3.57 (d, 2H, J = 7.16 Hz), 3.26
(dd, 1H, J = 14.0 and 6.1 Hz), 3.22 (dd, 1H, J = 12.47 and 1.7
Hz), 2.92 (m, 2H), 2.87 (q, 2H, J = 7.2 Hz), 1.17 (t, 3H, J = 7.2
Hz).13C NMR (D2O, ppm, d):171.95, 159.52, 158.54, 54.27,
53.61, 53.51, 52.45, 49.69, 49.60, 43.29, 42.43, 42.39, 9.48.
MS (ESI, H2O/CH3CN 1:1): m/z 162 (M+2H)2+, 323 (M+H)+.
[a]20D:-12° (H2O).
(19) Iddon, B.; Lim, B. L. J. Chem. Soc., Perkin Trans 1 1983, 3,
271-277.
(20) Breslow, R.; Hunt, J. T.; Smiley, R.; Tarnowski, T. J. Am.
Chem. Soc. 1983, 105, 5337-5342.
(21) Kirk, K. L. J. Heterocycl. Chem. 1985, 22, 57-59.
(22) Roberts, J. L.; Borromeo, P. S.; Poulter, C. D. Tetrahedron
Lett. 1977, 1621-1624.
(23) Sato, F.; Oguro, K.; Watanabe, H.; Sato, M. Tetrahedron Lett.
1980, 21, 2869-2872.
(24) Smith, J. G.; Dibble, P. W.; Sandborn, R. E. J. Org. Chem.
1986, 51, 3762-3768.
concentrated. The resulting crude (1.15g) was purified by
flash chromatography (70%CH3CN/1%MeOH/CH2Cl2) to
afford 4b (0.575g, 60%): mp 209-210 °C (recrystallization
from i-PrOH). 1H NMR (CDCl3, ppm, d):5.97 (br s, 1H, NH),
5.89 (d, J = 5.9 Hz, 1H, NH), 4.60 (br s, 1H), 4.52 (dd,
J = 15.3 and 8.2 Hz, 1H), 3.73-3.64 (m, 2H), 3.39 (m, 1H),
3.20 (br s, 1H), 2.96 (br s, 1H), 2.58 (br s, 1H), 1.39 and 1.38
(2 s, 9 H, t-Bu). 13C NMR (CDCl3, ppm, d):165.6, 155.4,
155.1, 80.2, 79.7, 60.7, 57.7, 54.6, 52.3, 47.0, 28.2. MS
(FAB): m/z 356 (M), 301, 245, 158, 57. Anal. Calcd for
C16H28N4O5 (356.43): C, 53.92; H, 7.92; N, 15.72. Found: C,
54.02; H, 7.81; N, 15.75. [a]20D:28° (CDCl3)
(25) Mander L. N.; Sethi, S. P. Tetrahedron lett. 1983, 24, 5425-
5428.
(26) Procedure for the preparation of 2-(1-tritylimidazolyl)acetal-
dehyde (10):1-Trityl-2-methylimidazole (11) was prepared as
described in the literature.21 To a -78 °C cooled solution of 1-
trityl-2-methylimidazole (mp 219-221 °C (EtOAc/ hexanes);
lit. 217-219 °C) (2g, 6.2mmol) in dry THF (60mL) n-BuLi
(1.6mol/L, 4mL) was added dropwise. After stirring for 50min
at -78 °C, freshly distilled HCO2Et (2.4mL, 31mmol) was
quickly added. The color of the reaction mixture changed from
red to pale yellow. After stirring for 15min at -78 °C, citric
acid (5%, 20mL) was added. The layers were separated, the
organic phase was diluted with EtOAc (50mL), dried
(Na2SO4), filtered and evaporated. The resulting solid was
triturated with hexanes (70mL) and EtOAc (5mL) to give
1.89g of a white solid (10, 87%, mp 103-118 °C) of enough
quality for the next reaction. 1H NMR (DMSO-d6, ppm, d):
enol 7.32 (m, Ar, 9H), 7.19 (m, Ar and H-imidazole, 7H), 6.62
(d, J = 1.4 Hz, H-imidazole, 1H), 6.57 (d, J = 6.1 Hz, CHO,
1H), 4.41 (d, J = 6.1 Hz, CH-imidazole, 1H). 13C NMR
(DMSO-d6, ppm, d):151.1, 148.9, 141.7, 129.4, 129.3, 128.5,
128.3, 128.1, 123.2, 119.3, 92.2, 74.7. MS (FAB): m/z 506,
353 (M+1), 243, 165.
(15) Procedure for the preparation of 6 and 7: To a suspension of 5
(0.44g, 1.25 mmol) in i-PrOH (14mL) a slurry of Raney nickel
(aprox. 3g, FLUKA 83440, previously washed 2 times with i-
PrOH) in i-PrOH (2mL) was added. The resulting mixture was
stirred at 50 °C for 1 h (followed by TLC), cooled and filtered
through celite. The crude product was purified by flash
chromatography (SiO2,TBME/Hexanes, 2:1) to give a white
solid (7, 0.33g, 92%): m. p. 218-220 °C. 1H NMR (CDCl3,
ppm, d):7.28 (br s, 1H, NH), 5.62 (d, J = 6.2 Hz, 2H, NH),
4.62 (m, 1H), 3.97 (m, 1H), 3.74 (br s, 1H), 3.29 (dd, J = 12.2
and 4.5 Hz, 2H), 2.72 (dd, J = 14.4 and 3.7 Hz, 1H), 2.70 (t,
J = 11.6 Hz, 1H), 2.46 (m, 1H), 1.45 and 1.43 (2 s, 9 H, t-Bu).
13C NMR (CDCl3, ppm, d):176.0, 155.2, 155.1, 79.8, 79.7,
55.0, 52.9, 51.7, 50.8, 43.7, 28.5, 28.3. MS (FAB): m/z 359
(M+1), 303, 247, 57. Compound 7 was prepared according to
the same procedure, using ethanol as solvent.
(27) deBenneville, P. L.; Macartney, J. H. J. Am. Chem. Soc. 1950,
72, 3073-3075. Marshall, J. A.;Johnson, W. S. J. Org. Chem.
1963, 28, 421-423. Ketcha, D. M.; Lieurance, B. A.
Tetrahedron Lett. 1989, 30, 6833-6836.
(28) Yong, Y. F.; Kowalski, J. A.; Lipton, M. A. J. Org. Chem.
(16) Ainsworth, C. J. Am. Chem. Soc. 1956, 78, 1635-1636.
(17) Kneeland, D. M.; Ariga, K.; Lynch, V. M.; Huang, C.-Y.;
Anslyn, E. V. J. Am. Chem. Soc. 1993, 115, 10042, 10055.
Muche, M.-S.; Göbel, M. W. Angew. Chem. Int. Ed. Engl.
1996, 35, 2126-2129. Metzger, A.; Lynch, V. M.; Anslyn, E.
V. Angew. Chem., Int. Ed. Engl. 1997, 36, 862-864.
(18) Procedure for the preparation of 3S, 7R-bis(4,5-dihydro-1H-
imidazol-2ylamino)-5-ethyl-2-keto-1,5-diazacyclooctane
hydrochloride (9): To a solution of 8 (300mg, 1.02mmol) in
5.5mL of DMF, triethylamine (440ml, 3.20mmol) was added
under argon. After stirring for 10 min the solution was filtered
and 4,5-dihydro-1H-imidazole-2-sulfonic acid
1997, 62, 1540-1542.
(29) Procedure for the preparation of 3,7-S-diguanidino-5-[2‘-
(imidazolyl)ethyl]-2-keto-1,5-diazacyclooctane
hydrochloride (1): compounds 6 (400mg, 1.12mmol) and 10
(790mg, 2.23mmol) were dissolved in CHCl3/EtOH 3:1
(10mL). The mixture was stirred for 3h under argon at r.t.
NaBH3CN (207mg, 2.8mmol) was added followed by the
slow addition of AcOH (2mL). After 3h the solution was
basified with sat. aq NaHCO3 and extracted with CH2Cl2. The
organic layers were dried (Na2SO4) and evaporated. Column
chromatography (SiO2, 2% MeOH/CH2Cl2) afforded 758mg
(95%) of 12. Compound 12 was dissolved in dry CH2Cl2 and
4M HCl in dioxane. After 2h stirring at 0 °C, the solvent was
evaporated, the white residue 13 was dried under high vacuum
and used without further purification. To a suspension of 13
(1.35g) and di-tert-butoxycarbonylthiourea (1.75g,
6.33mmol) in dry THF (21mL) was added Et3N (2.2mL) and
EDC (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide
hydrochloride, 1.21g, 6.33mmol). After 3h stirring under
argon at r.t., the mixture was washed three times with water,
dried (MgSO4) and evaporated. Column chromatography
(290mg,1.94mmol, dissolved in 8mL of DMF) was added
over 4h using a syringe pump. The mixture was stirred for 48h
at r.t. under argon. The resulting precipitate was collected by
filtration and washed with ether. The crude product was
adsorbed on a cation exchange column (Sephadex CM C-25,
3 x 10cm) and eluted with a salt gradient (0.1M-0.5M
NH4OAc). The product fractions were collected and
lyophilized. The acetate was converted to the chloride by
anion exchange (Dowex 1X8, Cl- form, Fluka, eluent CH3CN/
Synlett 1999, No. 12, 1875–1878 ISSN 0936-5214 © Thieme Stuttgart · New York

1878
J. A. Martinez-Perez et al.
LETTER
(SiO2, hexanes/EtOAc 3:1) afforded 906mg (44% from 12 to
14) of 14. Then 14 (188mg, 0.192mmol) was dissolved in 4N
aq HCl in dioxane (9mL) and water (1.2mL). After stirring
overnight at r.t., the solvent was removed and the residue
lyophilized. The white powder obtained was triturated with
EtOAc, filtered and dried under vacuum to afford 111mg of
impure 1. It was purified, following a known procedure30 by
conversion to the picrate salt, followed by two
C(3)); 3.76 (d, J = 15.5 Hz, 1H, H-C(8)); 3.69 (br s, 1H, H-
C(7)); 3.28 (dd, J = 2.5 and 15.5 Hz, 1H, H-C(8)); 3.07 (m,
6H, H-C(4), H-C(6), 2H-C(1‘), 2H-C(2‘)); 2.75 (m, J = 10.5
Hz, 1H, H-C(4)); 2.66 (br s, 1H, H-C(6)). 13C NMR
(D2O):174.5, 156, 145.3, 118.5, 58, 54, 52, 47, 42.5, 23. FAB-
MS: m/z 338 (M+H)+. mp 175-178 °C. [a]20D:+68° (H2O).
(30) Perreault, D. M.; Chen, X.; Anslyn, E. V. Tetrahedron 1995,
51, 2, 353.
recrystallisations from CH3CN. The picrate salt of 1 was
converted to the hydrochloride form by an ion exchange
column (Dowex 1X8, Cl- form, Fluka, eluent THF/H2O 1:1) to
afford 47mg (44%) of pure 1. 1H NMR(D2O, ppm, d):7.25 (s,
2H, H-C(3‘), H-C(4‘)); 4.58 (m, J = 4.7 and 10.5 Hz, 1H, H-
Article Identifier:
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Synlett 1999, No. 12, 1875–1878 ISSN 0936-5214 © Thieme Stuttgart · New York