Castagnoli, Neal, Jr.

Fawwaz, Rashid A

Freeman, Norman K

Tenforde, Tom

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Lawrence Berkeley National LaboratoryLBL PublicationsTitleNMR and IR Studies on the Tautomerism of 1-Ethyl-3-(3'-Dimethylaminopropyl) CarbodiimidePermalinkhttps://escholarship.org/uc/item/47b5x0j6AuthorsTenforde, TomFawwaz, Rashid AFreeman, Norman Ket al.Publication Date2023-09-06eScholarship.org Powered by the California Digital LibraryUniversity of California• - I • • ••- •-• • NMR AND IR STUDIES ON THE TAUTORISM OF 1 -ETHYL-3- (3 1  -DL\1E=a1I1T0PROPYL) CARDIfl4IDE Tom Tenl'orde*1  , Rashid A. Fawaz, and Norman K. Freeman Donner Laboratory, Laurence Berkeley Laboratory University of Callfornia, Berkeley, California 94720 Neal Castagnoli, Jr. Deparaent of Pharmaceutical Chemistry, School of Pharmacy University of California, San Francisco, California 94122 Journal of Organic Chemistry (In Press, 1972) / DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. 4 -1- Chemotherapy trials performed during the past year have demonstrated that 1-ethyl-3- (3 '-dimethylaminopropyl) carbodiimide (1), when administered as a saline solution of its hydrochloride salt, exerts a carcinostatic effect 2 3 on transplanted tumors in mice. Sheehan et a10 have suggested from ir studies that protonation of the tertiary amine of the carbodiimide 1 may lead to the formation of the tautomeric reduced pyriinidines 2-ethylaininb-313-dimethyl-314,516-tetrahydropyi±nidine chloride (4)  and/or 2-ethyitmino-3,3-dirxiethylperhydropyriinidine chloride (5). Titration data have established CH  - CH2 - N= C= N- (CR2)3  - N CH  CH 3 AAO • X •CH CR3  - CH2  - N = C = N - (CH - N- 2) B. _.. •3. \  CH  R = H, X = Cl B. = CR3, X = I H3 - CH2k-N) N CH3 CH2 N=CQJ R=H,X=Cl 5: R=H,X=Cl 6: RCH3,X1 • • 7:R=',CH3,X=I -2- that the PKa  of compound 1 is approximately 10.75 Consequently, 1 exists largely as the protonated species in aqueous solution at physiological pH. We therefore have undertaken spectroscopic studies to confirm the existence of structures 4 and/or 5, and to quantitate the relative percentages of isomeric species 23, 41 and 5 present in water at neutral pH. Information of this nature may prove to be of value both in understanding the mechanism of drug action against tumors, and in the synthesis of new potentially tautomeric carbodiirnides. When examined in aqueous solution or as a crystalline dispersion in nujol, the hydrochloride salt of 1 exhibits a weak absorption at 2128 corresponding to the fundamental antisymmetric -N= C= N- stretching mode.4  A strong band occurs at 1702 cm, characteristic of the -N=C stretching 5 mode present in structures 4 and 5. Infrared spectra of the meth-iodide derivative of 1 i water and nujol show a strong carbodimido band at 2128 with no absorption at 1702 cm-1. These observations are consistent with the anticipated N-methylation structure 3, and indicate that reaction of 1 with methyl iodide does not produce isomeric structures 6 and/or 7. Infrared spectra of the free carbodiiinide base, either in neat phase or in chloroform or unbuffered aqueous solution, are consistent with the open chain structure 1. Since the methiodide derivative of 1 must exist exclusively in the carbodiiinide form 3, the extinction coefficient for the -NC=N- band at 2128 cm- could be measured and was found to be 1.67 x 106 cm2/mole in water. Assuming the same extinction coefficient for the 2128 cm71 band observed in the aqueous solution ir spectrum of the hydrochloride salt of 1, it was calculated that 7.410 of this compound exists as the open chain carbodiiiriide hydrochloride 20 Spectra were recorded in solutions buffered over the pH -3— range 6 to 9, and no significaiit variation was noted in the strength of the carbodiiwide absorbance. Outside this pH range, carbodiimide hydrolysis prevented accurate measurements. In an effort to confirm and to extend the structural information obtained from ir data, ninr spectra of 1, its hydrochloride salt, and its inethiodide derivative 3were recorded in deuterium oxide. In the spectrum of the, methiodide derivative 3 (Fig. 1A, Table I), the two partially resolved triplets centered at 63.20 and 8 3.4-4 ppm can be assigned to the c and e met hylene proton resonances since all other signals can be unambiguously assigned. The difference in 5-values for the £ proton signals of the free base 1 and the methiodide derivative 3 Table I) is 0.95 ppm. Assuming a similar downfield shift of the e proton resonance for species 3 relative to 1, the triplet at b 3.20 ppm (A36e,=  0.92 ppm) must be assigned to the signal for protons e. Consequently, the 8 3.4-4 ppm signal is associated with the c mnethylene protons. The rmmr spectrum of the hydrochloride salt of 1 in deuterium oxide (Fig. 1B, Table I) indicates the presence of one major and one minor species. The weak singlet appearing at 6 2.92 ppm has been assigned to the resonance of the N,N-<Liuiethyl protons of the open, chain hydrochloride salt, structure 2. The intensity of this signal is approximately 8%. as great as that of the major gem-dimethyl proton signal at 8 3.41 ppm, and is consistent with the percentage of 2 calculated from ir spectral data. The upfield shift of this signal relative to the N-CH3  signals for the quaternary compounds considered here can be explained by localization of the positive charge predminantly on the proton bonded to the tertiary nitrogen.6 As a result of this charge distribution, the deshielding of the N-CH3  protons is less for species 2 than for the quaternary. compounds. -4- • Identification of the InajQr component present in the hydrochloride • salt of 1-can be made by comparison of chemical shift data for this compound and the free carbodilinide base 1 (Fig. 1B, Table I). In the spectrum of the hydrochloride salt of 1, the partially obscured triplet centered at 6 3,48 ppm can be assigned to the signal for the e protons since i.HC1ôf = 1-*1HCl8e = 1.20 ppm. The low field triplet at 6 3.86 ppm can then be assigned to the c proton signal. A comparison of the spectra of 1 and the hydrochloride salt of 1 also shows that A 1 8 = - 0.09 ppm and i-*i.HC18c = 0.59 ppm. Using these relative chemical shift data, we have assigned 4 as the predominant species present in the hydrochloride salt of 1for the following reasons. First, the deshielding effect of N-i in structure 4 is expected to be greater than that of the carbodiiinino nitrogen of 1, resulting in a downfield shift for the C proton signal.7 Second, the deshielding effect of the amino nitrogen of4is expected to be less than that of the carbodiimino nitrogen of 1, resulting in an upfield shift for the b proton signal. In the case of structure 5, one would predict the signal for the b protons to occur downfield, and the c proton signal upfield, relative to the corresponding signals for compound 1. • 1knr spectra were also recorded for the free carbodiiinide base 1 i neat phase and as a-solution in chloroform. In both cases, the observed chemical shifts and coupling constants were consistent with an open chain carbod.iimide' structure. In summary, the ii' and nmr studies presented here demonstrate that the hydrochloride salt of 1 in water at neutral pH exists as a mixture of two isomeric forms: 7.4% as 2 and 92.6% as 4. The methiodide derivative 3 and - • the free base 1 exist only as open chain ca.rbodiiinide structures. -5- EXPERfl€NTAL SECTION The hydrochloride salt of 1-ethyl-3-(3'--dimethylaminopropyl)ca.rbodii7nide (1) with an uncorrected nip of 109-1100 (lit3 nip 114-1150 ) was purchased from the Ott Chemical Company (Muskegon, Michigan). The derivative 1-ethyl-3-(3' -dimethylaminopropyl)carbodiimide methiodide (3) with an uncorrected nip of 90930  (lit3 mp 106.5-10750) was prepared from freshly distilled carbodiiinide base 1 and methyl iodide.3  Structure 3 and the hydrochloride salt of 1 i 50% methanol/50% acetone move on silica gel as single bands with Rf values of 065 and 0.71, respectively. Only trace amounts of impurities are present. Infrared spectra of these compounds in water and as nujol mulls demonstrate the absence of urea bands in the 1530-1680 cm range. As determined from the absorbance at 2128 cm, the hydrolysis of these compounds in water at neutral pH follows first order kinetics. At 370  C. the t1 for hydrolysis of the hydrochloride salt of 1. is 60 hrs, and for hydrolysis of3is 26 hrs. / -6— REFERENCES * To whom correspondence should be addressed. Supported by a postdoctoral fellowship from the Bay Area Heart Research Committee 1969-71, and fellowship No, 1-F02-CA-52469 from the National Cancer Institute 1971-72. This research was supported by U. S. Atomic Energy Commission contract W - 7405 - eng- 48 with the Lawrence Berkeley Laboratory. R. Fawaz and T. Tenforde, Proc. Am. Assoc. Cancer Res. j, 36 (1972). J. C. Sheehan, P. A, Cruickshank and G. L. Boshart, J. Org. Chem. 26, 2525 (1961). G. D. Neakins and R. J. Noss, J. Chem, Soc. (London), 993 (1957). C. N. R. Rao, "Chemical Applications of Infrared Spectroscopy," pp. 265-267. Academic Press, New York (1963). J. M. George, L. B. Kier and J. R. Hoyland, Mol. Pharinacol. 7, 328 (1971).. L. N. Jackman and S. Sternhefl, "Applications of Nuclear Haietic Resonance Spectroscopy in Organic Chemistry," 2nd ed., pp.80-81. Pergazuon, Oxford (1969). Melting points were measured on a Thomas-Hoover apparatus. Infrared spectra were recorded on a Perkin-Elmer Model 421 Spectrometer. Spectra of solutions were obtained using matched 0,018 nun CaF2 cells, Because of the weak absorbance of the hydrochloride salt of 1 at 2128 cri71 , measurements at this frequency in aqueous sblution were made by recording the transmittance at 5X scale expansion. Nmr spectra were recorded at ambient temperature on a Varian A-60A Spectrometer. / C. 7. Protons (b) a b C d e f g  ii 1.21 (t, J= 7 Hz) 3.26 (q, = 7) 3.27 (t, J = 6.5) 1.7 (in) 2.28 (t, 3 = 7) 2.21 (a) Table AA- 1.22 (t, J 7Hz) 3,31 (q, i= 7) 3.44 (t, J= 6.5) 2,1 (in) 3.20 (t, = 7) 3.16 (a) HU salt of 1 1.16 (t, J = 7Hz) 3.17 (q, i= 7) 3.86 (t, = 7) 202 (in) 3048 (t, = 6.5) 3.41 (s) 2.92 (a) 60 MHz Chemical Shift and Coupling Constant Data a (pm) Spectra were recorded in deuterium oxide with sodium 4,4-dimethyl-4- silapentane sulfonate (SDSS) as an internal reference standard (sDss = 0.0 ppn), Proton designations are the same as in Fig. 10 / / CAPTION FOR  FIGURE 1 Nrnr spectra at 60 MHt in deuterium oxide of (A) 1_ethyl_30L.diIaethyl_ azninopropyl)carbodiimide inethiodide and (B) the hydrochloride salt of 1-ethyl-3_(31 -diinethylaniinopropy1)carbodjimide0 Both spectra were recorded with sodium 4.,4-dimethyl-4-silapentane sulfonate (SDSS) as an internal reference standard (SDSS = 0e0 ppm). -9— Figure (a) (b) (c) (d) (e) CH3 CH 3 —CH2 —NCN—CH2 —CH2 —CH 2 —N--CH3 (f) "CH3 (a) (f) 1.. ppm, B 3 (f) Cl— H' j ,,CH3 CH2 —N=C=N—CH2--CH2—CH 2 —N CH 3 — Cl— (e) (f) CH3.,CH2 ' (a) CH 2 (d) (a) (b) I =± CH3_CH2_N_CNCH2 (c) H 1 ----  ( . tb) (c) (e) 4. . 3 ppm, (d) A 2  1   DSL 722 5179 

NMR and IR Studies on the Tautomerism of 1-Ethyl-3-(3'-Dimethylaminopropyl) Carbodiimide

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