J. Org. Chem. 1984,49, 2546-2551
2546
1449,840,810,778,764,756,728,718 cm-'; MS (CI) MH+, m / e 441 (31), 275 (17), 247 (100). Anal. Calcd. for C3Hs2: C, 92.68; H, 7.32. Found: C, 92.64; H, 7.36.
8,15,23,30-Tetramethyl[2.1.2.1]metacyclophane-trams ,traas-l,l6-diene (11C). N d H 4 (2.7 mg,0.07 mmol) was added to a solution of cyclophane 2B (minor isomer)2 (15.9 mg, 0.035 mmol) in wet THF (50 mL) and the mixture heated at reflux for 12 h. After the mixture had cooled, dilute HC1 was added and then dichloromethane. The organic layer was washed, dried, and evaporated, and the residue was mixed thoroughly with powdered N&H4 (13.5mg, 0.35 "01) and added in portions to CF3COOH (30 mL) at 0 OC under Nzwith vigorous stirring. After a further 20 min, aqueous NaHC03 solution was added and then dichloromethane. The organic layer was washed, dried, and evaporated, and the residue was recrystallized from cyclohexane/hexane to give 12.5 mg (81%)of colorleas crystals of 11C mp 305-307 OC; 'HNMR (90 MHz) 6 7.38-7.06 (m, 12 H, Ar H), 6.49 (s,4 H, -CH=), 4.20 (s,4 H, CH2),1.14 (8, 12 H, Ar CH,); IR (Kl3r) 1458,965 (trans-CH-CH), 848,779,769,759,710cm-';
MS (CI) MH', m / e 441 (lo),425 (lo),275 (20),249 (39), 247 (100). Anal. Calcd. for C3HS2: C, 92.68; H, 7.32. Found: C, 92.70; H,
-
7.30. Hydrogenation of Dienes 2C and 11C to 8C (12G). 30% Pd/C (3 mg) was added to a solution of the cyclophanediene 2C or 11C (15 mg) in dry benzene (10 mL), which was then stirred under 1 atm of Hz at 20 "C for 24 h. Removal of catalyst and then solvent yielded in both cases quantitativesamples of 8C (12G)
identical with the previously obtained samples (mp, 'H NMR, MS). Registry NO. lA, 90133-68-9; lB, 75404-52-3;lC, 90133-67-8; 2A, 90133-71-4;2B, 90133-70-3;2C, 90133-69-0;8A, 90133-73-6; 8B, 90133-72-5;8C,75397-87-4; 11A, 90133-74-7; 11B, 90133-75-8; 11C, 90133-76-9. Supplementary Material Available: Full variable temperature NMR data for compounds 12 and figures S1-S10 (10 pages). Ordering information is given on any current masthead page.
Charge-Shift Probes of Membrane Potential. Synthesis A. Hassner, D. Birnbaum, and L. M. Loew* Department of Chemistry, State University of New York,Binghamton, New York 13901 Received December 20, 1983
We are reporting two general synthetic approaches to a number of (aminostyry1)pyridinium dyes and their heterocyclicanalogues which are of interest as electrochromic probes for membrane potential. The two routes which involve palladium-catalyzed coupling or aldol condensation permit considerable structure variations to be introduced in the dyes. Some spectral properties of the dyes are discussed. The synthesis of cyanine, merocyanine, and styryl dyes has been based largely on a key condensation step between the heterocyclic nuclei. These dyes are especially useful as sensitizers in the photographic industry, and their syntheses have been thoroughly reviewed.' Hundreds of these dyes are commercially available. Cohen2 and Tasaki3 were the first to discover voltagedependent changes in fluorescence or transmittance characteristics of the squid giant axon which had been stained with a variety of dyes. It soon became apparent that the electrical properties of a variety of cell and membrane preparations could be studied in this way.4 We have been interested in the styryl class of dyes because of the possibility that they would respond to membrane potential changes by an electrochromic mechanisms5p6 The latter requires that the dyes should provide a response time which is able to follow the fastest of physiological events, and should be operative on a wide variety of membrane preparations. A number of (p-aminostyry1)pyridinium dyes 1 have I
appear to respond to voltage pulses via electrochromi~m.'~~ Such electrochromic dyes are amenable to theoretical design and are of intrinsic physical-chemical interest apart from the biological applications. The synthesis of these dyes has closely followed the aldol condensation strategy? In an effort to explore chromophores with more extended n-systems and dyes with u n u s 4 side chains it has become necessary to expand the aldol condensation methodology as well as to develop other general dye syntheses. The chromophoric system that has been most useful in our studies of membrane potential probes is exemplified by structure la. These molecules possess a t their polar
--a
b
C
A I-\
R-L ' -N? ' I
/R
B
I
been tested on model membrane systems and do indeed ~~~~~~~~~~~~
~
~
(1) Hamer, F. M. In "The Cyanine Dyes and Related Compounds";
Wiley, New York, 1964. (2) Cohen, L. B.; Salzberg, B. M.; Davilla, H. V.; Ross,W. N.; Landowne, D.; Waggoner, A. S.;Wang, C. H. J. Membr. Biol. 1974, 19, 1. (3) Tasaki, I. Ann. N. Y . Acad. Sei. 1974, 227, 247. (4) Freedman, J. C.; Lark, P. C. Int. Rev. Cytol. Suppl. 1981,12,177. (5) Loew, L. M.; Bonneville, G. W.; Surow, J. Biochemistry 1978,17, 4065.
(6) Loew, L. M. J . Biochem. Biophys. Meth. 1982, 6 , 243.
0022-3263/a4/1949-2546$01.50/0
la hydrophilic end a pyridinium salt moiety preferably in the form of an electrically ngutral zwitterion sulfonate (part a). This heterocyclic moiety is conjugated via an unsatu(7) Loew, L. M.; Scully, S.; Simpson, L.; Waggoner, A. S. Nature (London) 1979,281,497. (8) Loew, L. M.; Simpson, L. Biophys. J. 1981, 34,353. (9) Loew, L. M.; Simpson, L.; Hassner, A.; Alexanian, V. J . Am. Chem.
SOC.1979, 101, 5439.
0 1984 American Chemical Society
J. Org. Chem., Vol. 49, No. 14, 1984
Synthesis of Charge-Shift Probes Scheme I R
R
\/
2’
V2 2a, R = (CH,),SO,-
b, R = (CH,),SO,c , R = CH,
3a, R = n-hexyl b, R = n-butyl
6 ‘i R’
la, R = n-hexyl; R‘ = (CH,),SO,b, R = n-hexyl; R = (CH,),SO,c , R = n-hexyl; R = CH, d, R = n-butyl; R = (CH,),SO,e , R = n-butyl; R = (CH,),SO,f , R = n-butyl; R‘ = CH,
rated chain (part b) to an anilino group which possesses medium-length carbon chains attached to nitrogen (part c) to provide the lipophilic end of the molecule. Upon excitation, such a molecule, which binds to a membrane in an orientation perpendicular to the membrane surface,8$ undergoes a shift of the positive pole from one end of the ~ resonance structure molecular to the ~ t h e r P. u~t ~simply, A is the major contributor to the ground state whereas B more closely describes the first excited state. The electrical response of these molecules is dependent in part on their absorption maxima. Hence it was of interest to synthesize a series of related molecules in which parts a-c can be structurally altered and to test the effect of structure on the spectral properties of these molecules.
Synthetic Methodology 1. The Aldol Approach. The general approach toward dyes of type 1 is to link a heterocyclic unit a with an aromatic unit c via one or more double bonds (unit b), the latter preferably with an E stereochemistry. To this end we have employed the aldol strategy shown in Scheme I and the palladium-catalyzed coupling (Heck reaction)1° described in the following section. Scheme I requires a pyridinium derivative or analogous heterocycle capable of activating a properly positioned alkyl substituent toward base-catalyzed aldol condensation with an amino-substituted aromatic aldehyde.” The pyridinium salts 2 were prepared from 4-picoline with sultones or methyl iodine. The aldehydes 3 were obtained by Vilsmeier reaction of the corresponding N,N-disubstituted anilines. In addition to the synthesis of the orange-red la-d, we have used the strategy of Scheme I to obtain a variety of dyes as summarized in Tables I and 11. The red diene-linked dyes, 5, presented some stereochemical problems. While the stereochemistry of the double bonds in most compounds obtained by the aldol route are E (trans) as indicated by NMR coupling (Figure (10) Heck, R. F. Accs. Chem. Res. 1979, 12, 146. (11) The alternative condensation of an amino-substituted toluene with a pyridinecarboxaldehyde cannot be achieved. Neither does the aldol condensation proceed smoothly with nonquaternized 4-methylpyridine and the aminobenzaldehyde.
0, N+
i
