Download PDF
Synlett 2008(18): 2785-2790  
DOI: 10.1055/s-0028-1083566
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

2-Iminothiolane as a Useful Coupling Reagent for Polyamine Solid-Phase Synthesis

Frank Hahna, Klaus Müllenb, Ute Schepers*a
a LIMES-Institute Program Unit Membrane Biology and Lipid Biochemistry and Kekulé-Institut für Organische Chemie und Biochemie, University of Bonn, Gerhard-Domagk-Str. 1, 53121 Bonn, Germany
Fax: +49(228)737778; e-Mail: schepers@uni-bonn.de;
b Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
Further Information

Publication History

Received 9 May 2008
Publication Date:
15 October 2008 (online)

    Permissions and Reprints All articles of this category

Abstract

Here, the versatility of 2-iminothiolane to act as coupling reagent for solid-phase synthesis of polyamine conjugates is shown. This method, which supersedes the use of elaborate protection group strategies, allows the mild coupling of biomacromolecules and other functional moieties. Spermine conjugates with diverse maleimido building blocks were synthesized by a quick and selective reaction.

Key words

solid-phase synthesis - chemoselectivity - conjugation - polyamines - 2-iminothiolane

    References and Notes

  • 2 Foerg C. Merkle H.-P. J. Pharm. Sci.  2007,  97:  144 
    Google Scholar
  • 3 Hahn F. Schepers U. In Combinatorial Chemistry on Solid Supports   Vol. 278:  Bräse S. Springer; Berlin / Heidelberg: 2007.  p.135-208  
    Google Scholar
  • 4a Manku S. Laplante C. Kopac D. Chan T. Hall DG. J. Org. Chem.  2001,  66:  874 
    Google Scholar
  • 4b Kan T. Kobayashi H. Fukuyama T. Synlett  2002,  1338 
    Google Scholar
  • 4c Jönsson D. Tetrahedron Lett.  2002,  43:  4793 
    Google Scholar
  • 4d Nash IA. Bycroft BW. Chan WC. Tetrahedron Lett.  1996,  37:  2625 
    Google Scholar
  • 5 Hahn F. Schepers U. J. Comb. Chem.  2008,  10:  267 
    CrossrefGoogle Scholar
  • 6a Traut RR. Bollen A. Sun TT. Hershey JWB. Sundberg J. Pierce LR. Biochemistry  1973,  12:  3266 
    Google Scholar
  • 6b Jue R. Lambert JM. Pierce LR. Traut RR. Biochemistry  1978,  17:  5399 
    Google Scholar
  • 6c Miyata K. Kakizawa Y. Nishiyama N. Harada A. Yamasaki Y. Koyama H. Kataoka K. J. Am. Chem. Soc.  2004,  126:  2355 
    Google Scholar
  • 6d Tada T. Mano K. Yoshida E. Tanala N. Kunugi S. Bull. Chem. Soc. Jpn.  2002,  75:  2247 
    Google Scholar
  • 6e King TP. Li Y. Kochoumian L. Biochemistry  1978,  17:  1499 
    Google Scholar
  • 7 Gruneich JA. Diamond SL. J. Gene Med.  2007,  9:  381 
    CrossrefGoogle Scholar
  • 8a Bartlett MG. Buscht KL. Biol. Mass Spec.  1994,  23:  353 
    Google Scholar
  • 8b Singh R. Kats L. Blättler WA. Lambert JM. Anal. Biochem.  1996,  236:  114 
    Google Scholar
  • 8c Mokotoff M. Mocarski YM. Gentsch BL. Miller MR. Zhou JH. Chen J. Ball ED. J. Peptide Res.  2001,  57:  383 
    Google Scholar
1

For a review, see: Schepers U., Schmitz K., Hahn F., Bräse S.; Angew. Chem. Int. Ed.; submitted

9

Spectroscopic Data for Side Product 6 ¹H NMR (MeOD, 400 MHz): δ = 3.69 (t, J = 7.2 Hz, 2 H), 3.65 (t, J = 6.5 Hz, 2 H), 3.26 (t, J = 7.2 Hz, 2 H), 3.09 (t, J = 7.5 Hz, 2 H), 2.44 (tt, J 1 = 6.9 Hz, J 2 = 6.8 Hz, 2 H), 2.18 (tt, J 1 = 7.4 Hz, J 2 = 7.4 Hz, 2 H). ESI-MS: m/z = 159.1
[M + H]+.

10

Spectroscopic Data for Side Product 8 ¹H NMR (MeOD, 400 MHz): δ = 4.45 (dd, J 1  = 9.1 Hz, J 2 = 5.7 Hz, 1 H), 3.57 (q, J = 7.3 Hz), 3.16 (dd, J 1 = 17.9 Hz, J 2 = 9.2 Hz, 1 H), 3.08 (t, J = 7.6 Hz, 2 H), 3.05 (t, J = 7.7 Hz, 2H), 2.91 (dd, J 1  = 17.9 Hz, J 2 = 5.6 Hz, 1 H), 2.13 (m, 2 H), 1.17 (t, J = 7.2 Hz).

11

Spectroscopic Data for Compound 9
¹H NMR (MeOD, 400 MHz): δ = 3.89 (dd, J 1 = 9.1 Hz, J 2 = 2.9 Hz, 1 H), 3.52 (q, J = 7.2 Hz, 2 H), 3.38 (t, J = 7.1 Hz, 2 H), 3.19 (dd, J 1 = 18.5 Hz, J 2 = 9.1 Hz, 1 H), 3.03 (t, J = 7.7 Hz, 2 H), 2.97 (dd, J 1 = 13.4 Hz, J 2 = 6.8 Hz, 1 H), 2.79 (dd, J 1 = 13.5 Hz, J 2 = 7.1 Hz, 1 H), 2.61 (t, J = 7.7 Hz, 2 H), 2.46 (dd, J 1 = 18.6 Hz, J 2 = 3.7 Hz, 1 H), 2.08 (tt, J 1 = 7.1 Hz, J 2 = 7.1 Hz, 1 H), 2.01 (tt, J 1 = 7.2 Hz, J 2 = 7.2 Hz, 1 H), 1.13 (t, J = 7.2 Hz, 2 H). ESI-HRMS: m/z calcd for C13H25N4O2S+: 301.1693; found: 301.1686.

12

Ethylmaleimide, phenylmaleimide, and 3-maleimido-propionic acid were purchased from Sigma-Aldrich. The maleimides from entries 4-6 were prepared by the following procedure: 3-maleimidopropionic acid N-hydroxysuccinimide ester (3 equiv) and DIPEA (1 equiv) were dissolved in DMF, and amine (1 equiv) was added in the same volume of THF. The suspension was stirred for 8 h and THF was removed in vacuo. The remaining suspension was partitioned between CH3Cl and H2O, and the organic layer was washed with H2O (3 ×). The organic layer was dried over Na2SO4, and the product was purified by flash chromatography. The products were isolated in 47%, 49%, and 35% yield and analyzed by HRMS and ¹H NMR spectroscopy. In entry 5, CH2Cl2 was used as solvent instead of THF-DMF and DMAP (1 equiv) was added for additional activation.

13

Experimental Procedure Alkoxytrityl resin (100 mg) loaded with tris-Aloc-spermine (0.027 mmol, 1 equiv) were swollen in CH2Cl2 and a solution of Pd(PPh3)4 (6 mg, 0.005 mmol, 0.2 equiv) and of N,N′-dimethylbarbituric acid (33 mg, 0.214 mmol, 8 equiv) in CH2Cl2 (2 mL) were added. The suspension was agitated for 16 h at 40 ˚C. The resin was alternately washed with a solution of sodium N,N-dimethylaminodithiocarbamate in CH2Cl2-MeOH (4:1) and MeOH (3 ×), THF and MeOH (3 ×), and CH2Cl2 (3 ×). The resin was swollen in THF (1 mL) for 10 min and 2-iminothiolane (11 mg, 0.081 mmol, 3 equiv.) in H2O (200 mL) was added. The suspension was agitated for 2 min, then the respective maleimide (2 equiv) in THF (800 mL) was added, and the suspension was agitated for 1 h. The resin was washed with H2O, THF, MeOH (3 ×), and CH2Cl2 (3 ×). The crude product was cleaved from the resin with 1% TFA in CH2Cl2. The filtrate was combined with the filtrate of the CH2Cl2 and MeOH wash. In entry 5 the 5′-DMTr group was removed by quick treatment of the resin with 1% TFA in CH2Cl2 and subsequent washing of the polymer with a minimal amount of CH2Cl2-Et2O (2:1) until the filtrate is clear. The product was washed from the resin with CH2Cl2 and MeOH. The solvents were removed and the remaining compound was purified by preparative HPLC on C18 column with gradients of eluent A [95% TEAA (0.01 M, pH 7.0)-5% MeCN] and eluant B [5% TEAA (0.01 M, pH 7.0)-95% MeCN), or with eluant A (95% H2O-5% MeCN-0.1% AcOH) and eluant B (5% H2O-95% MeCN-0.1% AcOH).

14

Characterization of the Products of Entries 1-7 (Table 2)
Entry 1: ¹H NMR (400 MHz, MeOD): δ = 1.14 (t, J = 7.2 Hz, 3 H), 1.79 (m, 4 H), 2.06 (tt, J 1 = 7.7 Hz, J 2 = 7.3 Hz, 4 H), 2.13 (m, 2 H), 2.47 (dd, J 1 = 18.5 Hz, J 2 = 3.9 Hz, 1 H), 2.62 (t, J = 7.7 Hz, 2 H), 2.80 (dt, J 1 = 13.5 Hz, J 2 = 7.0 Hz, 1 H), 2.98 (dt, J 1 = 13.6 Hz, J 2 = 6.8 Hz, 1 H), 3.00-3.15 (m, 10 H), 3.19 (dd, J 1  = 18.5 Hz, J 2 = 9.1 Hz, 1 H), 3.40 (t, J = 7.1 Hz, 2 H), 3.53 (q, J = 7.3 Hz, 2 H), 3.90 (dd, J 1 = 9.1 Hz, J 2 = 3.8 Hz, 1 H). ESI-HRMS: m/z calcd [M + H]+: 429.3006; found: 429.3010.
Entry 2: ¹H NMR (400 MHz, MeOD): δ = 1.79 (br m, 4 H), 1.96-2.14 (m, 6 H), 2.60-2.70 (m, 3 H), 2.86 (dt, J 1 = 13.6 Hz, J 2 = 7.1 Hz, 1 H), 2.93-3.10 (m, 11 H), 3.39 (t, J = 6.5 Hz, 2 H), 3.32-3.40 (m, 1 H), 4.10 (dd, J 1 = 9.1 Hz, J 2 = 3.8 Hz, 1 H), 7.26-7.54 (m, 5 H). ESI-HRMS: m/z calcd [M + H]+: 477.3006; found: 477.3002.
Entry 3: ESI-HRMS: m/z calcd [M + H]+: 473.2905; found: 473.2907.
Entry 4: ¹H NMR (400 MHz, MeOD): δ = 1.67 (tt, J 1 = 6.7 Hz, J 2 = 6.7 Hz, 2 H), 1.73-1.88 (br m, 4 H), 2.00-2.14 (br m, 6 H), 2.50 (dd, J 1 = 17.9 Hz, J 2 = 3.6 Hz, 1 H), 2.44-2.70 (m, 2 H), 2.60-2.70 (m, 2 H), 2.82 (dt, J 1 = 13.9 Hz, J 2 = 6.5 Hz, 1 H), 2.93 (dt, J 1 = 13.8 Hz, J 2 = 6.9 Hz, 1 H), 3.04-3.24 (m, 15 H), 3.42 (t, J = 7.1 Hz, 2 H), 3.68-3.83 (m, 1 H), 3.90 (dd, J 1 = 9.2 Hz, J 2 = 3.9 Hz, 1 H), 7.80-8.11 (m, 4 H). ESI-HRMS: m/z calcd [M + 2H]²+: 357.6749; found: 357.6736.
Entry 5: ¹H NMR (400 MHz, MeOD): δ = 1.80-1.90 (m, 4 H), 2.00-2.18 (br m, 6 H), 2.21 (m, 1 H), 2.50 (m, 1 H), 2.58-2.68 (m, 3 H), 2.81 (m, 2 H), 2.95 (dt, J 1 = 13.1 Hz, J 2 = 6.5 Hz, 1 H), 3.00-3.30 (m, 12 H), 3.42 (t, J = 6.9 Hz, 2 H), 3.70-3.90 (m, 4 H), 3.93 (dd, J 1 = 9.0 Hz, J 2 = 3.9 Hz, 1 H), 4.03 (dt, J 1  = 3.4 Hz, J 2  = 3.5 Hz, 1 H), 4.39 (dt, J 1  = 6.8 Hz, J 2 = 6.5 Hz, 1 H), 6.09 (d, J = 7.8 Hz, 1 H), 6.22 (m, 1 H), 8.39 (br, J = 7.8 Hz, 1 H). ESI-MS: m/z = 682.36 [M + H]+, MS-FAB+: 682.4 [M + H]+.
Entry 6: ¹H NMR (400 MHz, MeOD): δ = 1.70-1.85 (m,
4 H), 1.89 (s, 3 H), 2.00-2.18 (m, 6 H), 2.25-2.40 (m, 2 H), 2.45-2.55 (m, 3 H), 2.63 (t, J = 7.6 Hz, 2 H), 2.81 (dt, J 1  = 13.3 Hz, J 2  = 7.2 Hz, 1 H), 2.91-3.28 (m, 12 H), 3.37-3.45 (m, 2 H), 3.70-3.97 (m, 7 H), 4.42 (dt, J 1  = 7.1 Hz, J 2 = 6.4, 1 H), 6.21 (m, 1 H), 7.87 (s, 1 H). ESI-HRMS: m/z calcd [M + H]+: 696.3861; found: 696.3859.
Entry 7: MS (MALDI+): m/z = 1583.16 [M + H]+. ESI-HRMS: m/z calcd [M + 2H]²+: 791.8509; found: 791.8456.

15

A proposed sequence would be: (1) Selective introduction of a protection group at the primary amine; (2) protection of the secondary amines; (3) removal of the protection group on the primary amine; (4) elongation with an S-protected building block; (5) deprotection of the thiol; (6) coupling of the thiol to a maleimide; (7) deprotection of the secondary amine.