Trans-2-aminocyclohexanols as pH-triggered molecular switches

Page  129 Issue in Honor of Prof. Nikolai Zefirov ARKIVOC 2005 (iv) 129-141 Trans-2-Aminocyclohexanols as pH-triggered molecular switches Vyacheslav V. Samoshin,* a,b Barbora Brazdova,b Vyacheslav A. Chertkov,c Dmitriy E. Gremyachinskiy,a,b Alla K. Shestakova,d Elena K. Dobretsova,a Lidia P. Vatlina,e Jing Yuan,b and Hans-Jörg Schneider f a Lomonosov Moscow State Academy of Fine Chemical Technology, Vernadsky Prospect 86, Moscow, 117571, Russia b Department of Chemistry, University of the Pacific, Stockton, CA 95211, USA c Department of Chemistry, Lomonosov Moscow State University, Moscow, 119899, Russia d State Research Institute of Chemistry and Technology of Organoelement Compounds, 111123, Moscow, Russia e Ushinsky Yaroslavl State Pedagogic University, Yaroslavl, 150000, Russia f Fachrichtung Organische Chemie der Universität des Saarlandes, D 66041 Saarbrücken, Germany E-mail: vsamoshin@pacific.edu; h-j.schneider@mx.uni-saarland.de Dedicated to Academician Nikolai S. Zefirov on his 70th birthday (received 24 Dec 04; accepted 21 Apr 05; published on the web 06 May 05) Abstract Cyclohexane-based conformationally controlled ionophores, the emerging new class of molecular switches, provide a new and promising approach to allosteric systems with negative cooperativity. Protonation of trans-2-aminocyclohexanols leads to dramatic conformational changes: due to an intramolecular hydrogen bond, a conformer with equatorial position of ammonio- and hydroxy-groups becomes predominant. Thus, these structures can serve as powerful conformational pH-triggers. The trans-2-aminocyclohexanol moiety has been used for pH-triggered conformational switching of a crown ether and a podand, and their complexes with potassium ion. Keywords: Molecular pH-switches, trans-2-aminocyclohexanols, cyclohexano crown-ether, conformational transmitters Introduction The development of molecular switches is of great current interest in view of their possible use in many applications, such as drug release, new sensor techniques or information storage and ISSN 1424-6376 Page 129 ©ARKAT USA, Inc

Page  130 Issue in Honor of Prof. Nikolai Zefirov ARKIVOC 2005 (iv) 129-141 transmission. Molecular switches are molecules that can reversibly change their conformations and related properties under external influence.1-3 Allosteric switches are host compounds containing at least two spatially separated binding sites that are conformationally coupled. When one site is occupied, it changes conformation, and this ‘signal’, mechanically transmitted by the structure of the molecule, induces a conformational change in the second site, thus increasing (positive cooperativity) or decreasing (negative cooperativity) its affinity to an appropriate guest. Negative cooperativity has been less explored than the positive, though it may be more interesting for applications, such as membrane transport, drug delivery, catalysis, etc. 1-3 For example, the presence of a particular effector compound, or a particular pH value could lead to the release or to the uptake of a biologically active substance. Cyclohexane-based conformationally controlled ionophores provide a new and promising approach to allosteric systems with negative cooperativity. Conformational control via introduction of various substituent(s) into a trans-fused six-membered cycle was proposed by us as a new principle for modification of the complexing ability of (cyclohexano)crown compounds and non-macrocyclic ionophores (podands).4-23 Similar ideas were suggested for cyclohexanebased podands by Raban et al.24-27 In these structures, a substituent plays a role of ‘conformational lever’, or ‘counterbalance’, and the cyclohexane moiety serves as a mechanical transmitter. The cyclohexane machinery can also mimic an allosteric effect by transmitting a conformational change (signal) from one complexing center (e.g. a macroheterocycle or podand) to another site, which results in an externally controlled conformational equilibrium of the type 1A 1B (Scheme 1).16,19-21,23 A change by external influence of non-bonded interactions between groups W and Z (and/or X and Y) in structures 1 will change the relative stability of conformers. By affecting these interactions one can control the position of conformational equilibrium of the type 1A 1B, thus controlling the shape and the complexing ability of the macrocycle or podand. These ideas were successfully explored also by Costero et al.,28-32 and were expanded by Koert et al.33-38 to cis-decaline and perhydroanthracene derivatives. X Z W Y X Z WY S2 S1 S1 S2 1A 1B Scheme 1 A promising type of a conformational trigger is provided by trans-2-aminocyclohexanol moiety. trans-1,2-Cyclohexanediols and trans-2-aminocyclohexanols are well known to strongly prefer the diequatorial conformation, in part due to an intramolecular hydrogen bonding between ISSN 1424-6376 Page 130 ©ARKAT USA, Inc

Page  131 R'OOC N O R'OOC R'OOC N OH R'OOC R R R R H S S R'OOC N O R'OOC R'OOC N OH R'OOC R R R R H S S Issue in Honor of Prof. Nikolai Zefirov ARKIVOC 2005 (iv) 129-141 vicinal substituents.20,23,39-42 Therefore, these structural moieties can be used as conformational counterbalances or locks. 2A 2B Scheme 2 We found 20 that the trans-2-morpholylcyclohexanol derivative (2, NR2 = morpholyl R’ = Et; Scheme 2) adopted predominantly conformation 2A in CDCl3, but conformation 2B in methanol or DMSO. This dramatic change, which exceeded 10 kJ/mol in terms of the relative conformational stability, was attributed to destruction of the stabilizing intramolecular OH···N hydrogen bond in 2A by the hydrogen bond acceptor solvents.20 Similar results were obtained earlier for trans-2-o-tolyl-cis-4-hydroxy(amino)-trans-5-amino(hydroxy)cyclohexanols 39 and some 5-alkyl-trans-2-aminocyclohexanols.40 Thus, the trans-2-aminocyclohexanol moiety provides a promising type of a rapid conformational trigger. As we suggested in a preliminary publication,23 another way to control such a conformational equilibrium is an addition of acid to protonate the amino group, and to generate a stronger intramolecular hydrogen bond of O···H-N+ type,23,39 e.g. in 3A (Scheme 3).23 This bond would stabilize conformation 3A, thus moving the ester groups away from each other, and decreasing their potential ability to interact with another molecule or ion, for example to form complexes like 1B. R'OOC R'OOC O N H + R R +H+ -H+ R'OOC R'OOC N R R H OH 3A 3B Scheme 3 Results and Discussion To further explore the use of trans-2-aminocyclohexanol moiety as a conformational trigger, we synthesized the model compounds 5-11 (Scheme 4), and evaluated their conformational behaviour in various conditions (Table 1). ISSN 1424-6376 Page 131 ©ARKAT USA, Inc

Page  132 Issue in Honor of Prof. Nikolai Zefirov ARKIVOC 2005 (iv) 129-141 R O COOEt COOEt m-CPBA O COOEt COOEt iPrOH, H2O R2NH HO NR OEt OEt 4 5-9 O 5 (R = Me), 6 (R = Et), 7 (R,R = -(CH2)4-), 8 (R,R = -(CH2)5-), 9 (R,R = -CH2CH2OCH2CH2-) (1) H(OCH2CH2)4OH, Py (2) m-CPBA COCl (3) piperidine, H2O, iPrOH COCl HOCOCl (3) piperidine, H2O, iPrOH HON O OO ON O OO OCOCl OO O 10 O OO O(1) Me(OCH2CH2)3OH, Py (2) m-CPBA OCH3 OCH3 11 Scheme 4 The position of the equilibrium 3A 3B (Scheme 3) was used as an indicator of the changes in intramolecular interactions. The conformer populations (nA, nB) and the free energy differences between conformers (.GB-A) were estimated by 1H NMR measurements in various solutions (Table 1). The conformer populations were determined using Eliel’s equation 43 for signal widths (W = SJHH) of the cyclohexane protons H1, H2, H4 and H5, measured as a distance between terminal peaks of a multiplet: Wobserved = WAnA + WBnB. The signal widths for individual conformers were estimated from measurements for compounds 5-11 and for closely related cyclohexane derivatives with completely biased conformational equilibrium:16-20,23,44,45 WA = 25.7 Hz (25.0 Hz for 5, 7, 9) and WB = 9 Hz for HOH; WA = 26.6 Hz (25.5 Hz for 5, 7, 9) and WB = 10 Hz for HNR2; and WA = 9 Hz and WB = 30 Hz for HCOOR’. The more accurate estimations were usually obtained from the data for HOH (H5) signal. We did not use the averaged chemical shifts for the equilibrium estimations because of their general sensitivity to temperature, to the nature of a solvent, the complex formation, additives, etc. ISSN 1424-6376 Page 132 ©ARKAT USA, Inc

Page  133 Issue in Honor of Prof. Nikolai Zefirov ARKIVOC 2005 (iv) 129-141 Table 1. 1H NMR data (400 MHz) and conformational parameters HOH HN HCOOR (2) HCOOR (1) Compound, solvent, nA, .GB-A, and additives a) % kJ/mol d W, Hz d W, Hz d W, Hz d W, Hz b) 5 in C6D12 3.36 24.5 2.2 3.16 <17 3.16 <17 > 95 > 7.5 b) 5 in CDCl3 3.39 24.9 2.2 3.2 11 3.2 11 > 95 > 7.5 5 in CD3OD 3.93 14.9 2.16 15.1 3.08 21.8 2.99 21.1 35 -1.5 b) 6 in C6D12-CCl4 3.21 25.5 2.4 3.13 11 3.09 11 ~100 > 9 b) 6 in CDCl3 3.41 25.6 2.5 3.25 11 3.21 11 ~100 > 9 b)<23 b)<23 b) 6 in CD3OD 3.71 21.0 2.5 3.2 3.2 72 2.3 + AcOH 3.89 25.7 3 b) 3.75 (7) c) 3.75 (7) c) ~100 > 9 7 in CDCl3 3.72 16.8 2.36 16.9 3.1 < 23 3.1 < 23 44 -0.6 7 in CD3OD 4.02 10.6 2.30 10 3.01 25.3 2.98 26.4 10 -5.4 b)b) + AcOH 3.84 22.4 3.16 23.0 3.3 3.3 85 4.3 b)b)b) +CF3COOH 3.80 24.1 3.3 3.3 3.3 94 7 b)b) 8 in C6D12-CCl4 3.35 24.8 2.22 26.5 3.2 3.2 > 95 > 7.5 8 in CDCl3 3.38 25.5 2.2 b) 3.20 (10) c) 3.20 (10) c) ~100 > 9 8 in CD3OD 3.81 18.4 2.23 18.7 3.12 17.7 3.05 17.2 56 0.6 + AcOH 3.85 25.5 3.11 26.4 3.36 (12) c) 3.3 b) ~100 > 9 + KI 3.82 18.5 2.23 18.6 3.12 17.5 3.07 17.1 56 0.6 9 in CDCl3 3.48 24.5 2.25 24.6 3.24 (13) c) 3.24 (13) c) > 95 > 7.5 20 9 in CD3OD 3.98 14.4 2.23 14.8 3.07 22.4 2.97 21.6 35 -1.5 20 9 in (CD3)2SO 3.94 (11) c) 2.12 (16) c) 2.91 25.2 2.75 24.5 25 -2.7 20 b)b) 10 in CDCl3 3.47 25.5 2.33 26 3.3 3.3 > 95 > 7.5 10 in CD3OD 3.79 20.1 2.29 20.5 3.22 18 b) 3.17 18 b) 65 1.5 23 b)b) + AcOH 3.89 25.7 3.12 26.6 3.4 3.4 ~100 >9 23 + KI 3.92 17.1 2.3 c) 3.19 (19) c) 3.13 b) 49 -0.1 23 b)b) +KI +AcOH 3.95 25.7 3.20 26.6 3.4 3.4 ~100 >9 23 11 in CD3OD 4.02 14.7 2.29 14.6 3.20 22.1 3.09 21.3 35 -1.5 23 b)b) + AcOH 4.01 25.4 3.20 ~25 c) 3.4 3.4 ~100 >9 23 c)b)b) + KI 4.12 12 2.27 3.2 3.2 20 -3.5 23 +KI+AcOH 4.01 25.1 3.22 26 3.45 11 3.40 11 95 7.5 23 a) Acid and/or salt were added in large excess. b) Partially or completely overlapped with other signals. c) A width at half-height of a poorly resolved multiplet. In accordance with the preliminary observations,20,23 all the studied molecules, except the pyrrolidinyl derivative 7, strongly prefer the conformation 2A (Scheme 2) in nonpolar solvents C6D12-CCl4 (1:1) and CDCl3. The equilibrium switches to conformation 2B in CD3OD. ISSN 1424-6376 Page 133 ©ARKAT USA, Inc

Page  134 Issue in Honor of Prof. Nikolai Zefirov ARKIVOC 2005 (iv) 129-141 Apparently, methanol effectively disrupts the intramolecular OH···N hydrogen bond that stabilizes 2A. The addition of excess acetic acid causes an opposite switch to conformation A, even in methanol solutions (3A, Scheme 3). Trifloroacetic acid produces a stronger effect. The power of this conformational pH-trigger has been estimated from the measurements for compound 7 as = 12 kJ/mol (Table 1). Hydrogen bonds of both OH···N and O···H-N+ types are known to convert a chair ring into a twist conformation in trans-aminohydroxy steroids 46,47 and some other conformationally locked structures.42,44 This acid-induced twisting of six-membered cycles indicates that the actual power of such triggers may be well above 20 kJ/mol. The latter fact also points out that a relative flexibility of cyclohexane ring sets a natural limit to the effective power of conformational tools (levers, locks, counterbalances) in such systems. If the power applied to both ends of the system exceeds the energy difference between the chair and twist-forms of cyclohexane (23-26 kJ/mol 48), then the ring may be screwed (for the relevant discussion see 13,17,27,42,44,49). Similar to the simpler model 8, the conformation A is somewhat preferred for the podand 10 (Table 1, Scheme 5).23 The conformation 10A is slightly more predominant than 8A in methanol solution. By contrast, the crown ether 11 prefers the conformation 11B with both ester groups equatorial (Table 1, Scheme 6), which can be attributed to a ‘contraction effect’ 4-7,9,13,15-18,21,23 of the macrocycle. N OH N OH 10A OO OO O O O O O K OO O OO O + N OH10B O O O O OO OO O O O O O O K+ H+ N O H H + OO OO O O O O O O O 10A.H+ 10B.K+ Scheme 5 ISSN 1424-6376 Page 134 ©ARKAT USA, Inc

Page  135 Issue in Honor of Prof. Nikolai Zefirov ARKIVOC 2005 (iv) 129-141 As all other studied structures, both ionophores demonstrate a dramatic switch to conformation A (A·H+) with excess acid (Table 1, Schemes 5,6). The power of this conformational trigger has been estimated from the measurements for compound 11 as = 10.5 kJ/mol. O OO O N O OO O N O OH O O OO O OH 11A 11B N OH K+ H+ O O O O K O O +ON O H H + OO OO O O O 11A.H+ 11B.K+ Scheme 6 The macrocycle in 11 and the polyether chains in 10 should be able to complex metal ions, thus providing a second binding site required for modelling of a negative allosteric effect. The necessary geometrical arrangement for such complexation can be achieved only in conformations 10B and 11B. When methanolic solutions of 10 or 11 were saturated with KI, the conformational equilibria were shifted to these B conformations (Table 1, Schemes 5,6) with a relatively small power of approximately 1.5-2 kJ/mol.23 Addition of excess acetic acid to these solutions completely switched the equilibrium back to conformations 10A and 11A. By contrast, the conformational equilibrium for the related non-complexing compound 8 was indifferent to the addition of potassium salt (Table 1). There is a substantial difference in positions of conformational equilibria for similar structures 5-9 with different NR2 groups. The preference for conformation A (.GB-A, in CD3OD) decreases in order (Table 1): Et2N (2.3 kJ/mol) > piperidyl (0.6) > Me2N (-1.5) ~ morpholyl (-1.5) > pyrrolidyl (-5.4) ISSN 1424-6376 Page 135 ©ARKAT USA, Inc

Page  136 Issue in Honor of Prof. Nikolai Zefirov ARKIVOC 2005 (iv) 129-141 This order shows poor correlation with the effective bulkiness of NR2 groups, i.e. their Avalues. As estimated by simple calculations (PCMODEL molecular mechanics 50) for R2Ncyclohexanes with no account for solvent effects, they are: Et2N (6.7 kJ/mol) > piperidyl (5.1) > pyrrolidyl (4.3) ~ Me2N (4.2) = morpholyl (3.6) However, the similar PCMODEL calculations for trans-2-R2N-cyclohexanols, which included an intramolecular OH···N hydrogen bond, produced the preference for the diequatorial conformation (equivalent to A) that qualitatively parallels the experimental order for compounds 5-9: Et2N (17.5 kJ/mol) = piperidyl (17.2) > Me2N (15.2) = morpholyl (14.9) > pyrrolidyl (8.5) Apparently, the geometrical requirements of the intramolecular hydrogen bond play an important role. The formation of hydrogen bond of OH···N, or O···H-N+ type forces NR2 group to adopt a conformation, which is different from its optimum conformation. In other words, the optimum conformations of different NR2 groups are not equally suited to the formation of hydrogen bond with the vicinal OH group. The magnitude of this additional strain depends on the structure of NR2. A similar observation was made for trans-2-amino- and trans-2dimethylamino- cyclohexanols,49 where the net gauche-attraction between OH and NR2 (in C2Cl4) was stronger for NH2 than for the more basic NMe2 group (3.8 kJ/mol and 2.5 kJ/mol, respectively). However, if the intramolecular hydrogen bond is not included, and the OH group points away from NR2 group (which may be the case in methanol solution), the calculated preference for the diequatorial conformation A for trans-2-R2N-cyclohexanols still parallels the experimental order for 5-9: Et2N (10.3 kJ/mol) > piperidyl (8.9) > morpholyl (8.3) = Me2N (7.5) > pyrrolidyl (0.3) Evidently, the steric restrictions imposed by the vicinal oxygen may be sufficient to force the equatorial dialkylamino group into non-optimal position thus affecting the conformational preferences of trans-2-R2N-cyclohexanols. Conclusions The results of the present study prove that the trans-2-aminocyclohexanol moiety can be used as a conformational pH-trigger for the control of the complex formation by various crown ethers and podands via switching of their preferred conformation. The strong conformational coupling of two different binding sites in compounds like 10 or 11 should allow the development of new ISSN 1424-6376 Page 136 ©ARKAT USA, Inc

Page  137 Issue in Honor of Prof. Nikolai Zefirov ARKIVOC 2005 (iv) 129-141 heterotropic allosteric systems with high negative cooperativity, which may be especially useful for a selective membrane or drug transport. The variation of NR2 groups allows a broad tuning of the conformational equilibrium, and thus of the complexing ability of these allosteric ionophores. In addition, the basicity of amino functions could be tuned for a response within a narrow pH range, in which such a switchable system could then liberate or bind drugs or toxic compounds. Experimental Section General Procedures. 1H NMR spectra were recorded on Varian VXR-400 (400 MHz) instrument. 13C NMR spectra were recorded on Varian Mercury-300 (75.5 MHz) instrument. The signals were assigned using COSY, HETCOR and homonuclear spin-spin decoupling techniques. Exact mass measurements were performed on the JEOL LCMate double-focusing mass spectrometer (Peabody, MA, USA) equipped with atmospheric pressure chemical ionization source at a resolving power of 5000 with polyethyleneglycol as an internal reference. The MS/MS spectra were obtained using the Varian 1200L triple quadrupole mass spectrometer (Walnut Creek, CA, USA) with electrospray source. 20,30 20 23 23 The compounds 4,9, 10, 11, and their precursors 14,15 have been described previously. General procedure for the reaction of epoxides with amines Epoxide 4 (0.73 g, 3 mmol) and amine (10 mmol) were stirred in a mixture of 1 ml water and 1 ml isopropanol for 15 h at r.t. The reaction mixture was evaporated in vacuo, and the product was purified by column chromatography (silica gel, ethyl acetate). A commercial 40% aqueous dimethylamine was used for the preparation of compound 5. All products were colorless viscous liquids. trans-1,2-Bis(ethoxycarbonyl)-cis-4-hydroxy-trans-5-dimethylaminocyclohexane (5). Yield: 34%. 1H NMR (400 MHz, CD3OD): d 1.235 (t, 3H, CH3), 1.240 (t, 3H, CH3), 1.77 (ddd, H3), 1.83 (ddd, H6), 2.0 (m, H6), 2.03 (m, H3), 2.16 (dt, H5), 2.27 (s, 6H, NCH3), 2.99 (dt, H1), 3.08 (dt, H2), 3.93 (dt, H4), 4.1 (m, 4H, OCH2Me), 4.76 (s, OH). 13C NMR (75 MHz, CD3OD): d 175.82, 175.66 (C=O), 66.79 (C5), 66.36 (C4), 62.05, 61.99 (OCH2Me), 42.19 (CH3N), 41.18 (C2), 41.11 (C1), 32.37 (C3), 24.50 (C6), 14.52 (CH3). MS/MS m/z (rel. intensity): 72.0 (21), 79.2 (12), 95.4 (50), 99.3 (16), 113.3 (23), 123.2 (54), 141.4 (28), 150.7 (27), 169.1 (100), 196.7 (51), 242.3 (15), 270.3 (18), 288.2 ([M+H]+, 14). HRMS: C14H25NO5 requires [M+H]+ 288.1811, found 288.1855. trans-1,2-Bis(ethoxycarbonyl)-cis-4-hydroxy-trans-5-diethylaminocyclohexane (6). Yield: 41%. 1H NMR (300 MHz, CD3OD): d 1.04 (t, 6H, CH3), 1.25 (t, 3H, CH3), 1.26 (t, 3H, CH3), 1.62 (ddd, H3a), 1.66 (ddd, H6a), 2.11 (m, H6e), 2.25 (m, H3e), 2.5 (m, 3H, CH2N + H5), 2.65 (m, 2H, CH2N), 3.16 (m, H1 + H2), 3.68 (dt, H4), 4.15 (m, 4H, OCH2Me). 4.85 (s, OH). 13C NMR ISSN 1424-6376 Page 137 ©ARKAT USA, Inc

Page  138 Issue in Honor of Prof. Nikolai Zefirov ARKIVOC 2005 (iv) 129-141 (75 MHz, CD3OD): d 175.51, 175.39 (C=O), 66.91 (C4), 62.15 (C5), 62.06, 62.03 (OCH2Me), 44.24 (CH2N), 41.95 (C1/2), 41.54 (C2/1), 32.42 (C3), 23.95 (C6), 14.57, 14.53 (OCH2CH3), 13.64 (NCH2CH3). MS/MS m/z (rel. intensity): 73.7 (11), 95.3 (44), 99.8 (20), 113.1 (19), 123.2 (27), 141.3 (30), 151.1 (17), 169.4 (100), 196.9 (27), 224.4 (16), 270.4 (15), 298.3 (17), 316.3 ([M+H]+, 27). HRMS: C16H29NO5 requires [M+H]+ 316.2124, found 316.2157. trans-1,2-Bis(ethoxycarbonyl)-cis-4-hydroxy-trans-5-pyrrolidylcyclohexane (7). Yield: 77%. 1H NMR (400 MHz, CD3OD): d 1.225 (t, 3H, CH3), 1.230 (t, 3H, CH3), 1.84 (m, 4H, CH2 pyrrolidyl), 1.9-2.05 (m, 4H, CH2), 2.30 (m, H5), 2.62 (m, 4H, CH2N), 2.98 (dt, H1), 3.01 (dt, H2), 4.02 (br.q, H4), 4.1 (m, 4H, OCH2Me), 4.88 (s, OH). 13C NMR (75 MHz, CD3OD): d 177.05, 177.00 (C=O), 67.36 (C4), 65.82 (C5), 61.69 (OCH2Me), 52.71 (CH2N), 40.61 (C1), 40.50 (C2), 31.45 (C3), 28.24 (C6), 24.33 (CH2 pyrrolidyl), 14.51 (CH3). MS/MS m/z (rel. intensity): 70.6 (18), 79.2 (12), 96.5 (80), 108.2 (10), 113.0 (21), 123.3 (30), 141.2 (31), 149.8 (35), 169.3 (100), 196.5 (39), 222.4 (38), 240.3 (22), 268.3 (40), 296.3 (30), 314.3 ([M+H]+, 38). HRMS: C16H27NO5 requires [M+H]+ 314.1967, found 314.1957. trans-1,2-Bis(ethoxycarbonyl)-cis-4-hydroxy-trans-5-piperidylcyclohexane (8). Yield: 56%. 1H NMR (400 MHz, CD3OD): d 1.24 (t, 6H, CH3), 1.44 (m, 2H, CH2 piperidyl), 1.57 (m, 4H, CH2 piperidyl), 1.69 (ddd, H3), 1.76 (ddd, H6), 2.08 (dddd, H6), 2.16 (dddd, H3), 2.23 (dt, H5), 2.42 (m, 2H, CH2N), 2.59 (m, 2H, CH2N), 3.05 (m, H1), 3.12 (m, H2), 3.81 (dt, H4), 4.14 (m, 4H, OCH2Me), 4.87 (s, OH). 13C NMR (75 MHz, CD3OD): d 175.90, 175.75 (C=O), 66.46 (C4), 66.41 (C5), 61.94 (OCH2Me), 51.72 (CH2N), 41.60 (C1), 41.23 (C2), 32.36 (C3), 27.45 (CH2 piperidyl), 25.85 (CH2 piperidyl), 24.20 (C6), 14.56, 14.53 (CH3). MS/MS m/z (rel. intensity): 85.3 (16), 95.5 (54), 99.5 (12), 112.8 (35), 123.1 (42), 141.5 (28), 151.2 (10), 169.6 (100), 197.2 (16), 208.6 (23), 236.5 (24), 254.4 (16), 282.6 (34), 310.5 (35), 328.3 ([M+H]+, 61). HRMS: C17H29NO5 requires [M+H]+ 328.2124, found 328.2146. trans-1,2-Bis(ethoxycarbonyl)-cis-4-hydroxy-trans-5-morpholylcyclohexane (9).20 Yield: 46%. 1H NMR (300 MHz, CD3OD): d 1.232 (t, 3H, CH3), 1.234 (t, 3H, CH3), 1.77 (ddd, H3), 1.87 (ddd, H6), 1.99 (dt, H6), 2.03 (ddd, H3), 2.23 (dt, H5), 2.48 (m, 2H CH2N), 2.57 (m, 2H CH2N), 2.97 (dt, H1), 3.07 (dt, H2), 3.69 (t, 4H, OCH2 morpholyl), 3.98 (dt, H4), 4.12 (m, 4H, OCH2Me), 4.85 (s, OH). 13C NMR (75 MHz, CD3OD): d 176.36, 176.14 (C=O), 68.31 (OCH2 morpholyl), 65.68 (C4), 65.41 (C5), 61.86, 61.84 (OCH2Me), 51.49 (CH2N), 41.01 (C1), 40.88 (C2), 31.87 (C3), 24.74 (C6), 14.53 (CH3). MS/MS m/z (rel. intensity): 87.8 (16), 95.3 (43), 99.5 (10), 113.8 (45), 123.4 (34), 141.2 (27), 151.3 (19), 169.2 (100), 197.4 (21), 210.3 (20), 238.3 (43), 284.3 (17), 312.3 (24), 330.2 ([M+H]+, 22). HRMS: C16H27NO6 requires [M+H]+ 330.1917, found 330.1898. trans-1,2-Bis(3,6,9-trioxadecyloxycarbonyl)-cis-4-hydroxy-trans-5-piperidylcyclohexane (10). Yield: 44%. 1H NMR (400 MHz, CD3OD): d 1.47 (m, 2H, CH2 piperidyl), 1.59 (m, 4H, CH2 piperidyl), 1.69 (ddd, H3), 1.76 (ddd, H6), 2.14 (dddd, H6), 2.24 (dddd, H3), 2.29 (m, H5), 2.44 (m, 2H, CH2N), 2.64 (m, 2H, CH2N), 3.17 (m, H1), 3.22 (m, H2), 3.35 (s, 6H, OCH3), 3.53 (dd, 4H, CH2OMe), 3.63 (m, 12H, OCH2), 3.70 (t, 4H, OCH2), 3.79 (dt, H4), 4.26 (m, 4H, COOCH2), 4.57 (s, OH). 13C NMR (75 MHz, CD3OD): d 174.69, 174.37 (C=O), 72.97, 71.55, ISSN 1424-6376 Page 138 ©ARKAT USA, Inc

Page  139 Issue in Honor of Prof. Nikolai Zefirov ARKIVOC 2005 (iv) 129-141 71.37, 71.36, 70.02, 70.00 (OCH2CH2O), 67.82 (C5), 65.90 (C4), 65.15, 65.09 (COOCH2), 59.10 (OCH3), 51.31 (CH2N), 41.74 (C1), 41.57 (C2), 33.24 (C3), 25.83, 24.32 (CH2 piperidyl), 23.58 (C6). MS/MS m/z (rel. intensity): 59.3 (14), 103.0 (16), 112.3 (22), 123.0 (11), 125.4 (14), 162.3 (12), 167.1 (22), 190.1 (60), 208.3 (23), 236.4 (21), 254.0 (13), 354.2 (51), 372.0 (11), 382.0 (12), 400.2 (64), 546.2 (100), 564.1 ([M+H]+, 65). HRMS: C27H49NO11 requires [M+H]+ 564.3384, found 564.3367. trans-19-Hydroxy-20-piperidyl-2,16-dioxo-3,6,9,12,15-pentaoxa-trans-bicyclo[15.4.0] heneicosane (11). Yield: 56%. 1H NMR (400 MHz, CD3OD): d 1.48 (m, 2H, CH2 piperidyl), 1.60 (m, 4H, CH2 piperidyl), 1.75 (ddd, H3), 1.83 (ddd, H6), 2.03 (dddd, H6), 2.08 (dddd, H3), 2.29 (dt, H5), 2.47 (m, 2H, CH2N), 2.59 (m, 2H, CH2N), 3.09 (dt, H1), 3.20 (dt, H2), 3.57 (t, 2H, OCH2), 3.65 (m, 6H, OCH2), 3.71 (t, 4H, OCH2), 4.02 (dt, H4), 4.11 (m, 2H, COOCH2), 4.33 (m, 2H, COOCH2), 4.81 (s, OH). 13C NMR (75 MHz, CD3OD): d 175.68, 175.53 (C=O), 71.74, 71.68, 69.80 (OCH2CH2O), 66.38 (C5), 65.90 (C4), 65.28, 65.20 (COOCH2), 51.88 (CH2N), 41.52 (C1), 41.34 (C2), 33.42 (C3), 25.56, 25.02 (CH2 piperidyl), 24.40 (C6). MS/MS m/z (rel. intensity): 123.6 (12), 149.5 (14), 167.5 (48), 190.4 (34), 195.5 (23), 213.3 (18), 254.4 (13), 384.6 (14), 412.7 (56), 430.3 ([M+H]+, 100). HRMS: C21H35NO8 requires [M+H]+ 430.2441, found 430.2483. Acknowledgements This research was supported by INTAS (Grant 94-1914), the Russian Foundation for Basic Research (Grant 94-03-09296), and the Department of Chemistry, University of the Pacific. Eberhardt Research Fellowship from University of the Pacific is gratefully acknowledged by V.V.S. Authors thank Dr. Andreas Franz, and Dr. Xiaoyi Hu (UOP) for their help in acquisition of MS data. References 1. Molecular switches; Feringa, B. L., Ed.; Wiley-VCH: Weinheim, Chichester, 2001. 2. Schneider, H.-J.; Yatsimirsky, A. Principles and Methods in Supramolecular Chemistry; Wiley: Chichester, New York, 2000. 3. Takeuchi, M.; Ikeda, M.; Sugasaki, A.; Shinkai, S. Acc. Chem. Res. 2001, 34, 865. 4. Samoshin, V. V.; Subbotin, O. A.; Zelenkina, O. A.; Zefirov, N. S. Zh. Org. Khim. 1986, 22, 2231 (Russ. J. Org. Chem. 1986, 22, 2004). 5. Samoshin, V. V.; Zelenkina, O. A.; Subbotin, O. A.; Zefirov, N. S. Zh. Org. Khim. 1987, 23, 1319 (Russ. J. Org. Chem. 1987, 23, 1192). 6. Samoshin, V. V.; Zelenkina, O. A.; Yartseva, I. V.; Zefirov, N. S. Zh. Org. Khim. 1987, 23, 2244 (Russ. J. Org. Chem. 1987, 23, 1984). ISSN 1424-6376 Page 139 ©ARKAT USA, Inc

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