Clicked AC regioisomer cationic cyclodextrins for enantioseparation

Abstract

Novel AC regioisomer cationic cyclodextrins have been successfully prepared with azide/alkyne click chemistry. The clicked CDs were explored for the enantioseparation of acidic racemates in capillary electrophoresis.

---

Chiral separations have attracted significant attention in academia and industry for both analytical and preparative purposes.^1,2 Capillary electrophoresis (CE) has been demonstrated as a powerful analytical technique in the field of pharmaceutical,^3,4 agrochemical,⁵ clinical and food analysis.^6–10 Although the library of chiral selectors is rather large, cyclodextrins (CD) and their derivatives have been considered to be the most useful selectors in chiral CE.^11,12 On the basis of practical separations, selectively modified CD derivatives prepared by converting hydroxyl groups to functional groups can afford repeatable enantioseparation in run–run or batch–batch processes.^13,14 Among various CD derivatives that are employed for chiral CE, most are functionalized through traditional nucleophilic and electrophilic reactions with reactive groups such as amino, carboxylic and sulfo groups.

However, conventional methods occasionally produce CD derivatives with relatively low selectivity and efficiency. Click chemistry, coined by Sharpless, is a newly demanding chemical approach resulting in high efficiency and little or no side products under mild reaction conditions.¹⁵ Extensive reports have explored the copper-catalyzed azide/alkyne click reaction. The mechanism of this ligand-free catalyzed cycloaddition reaction was investigated by Rodionov.¹⁶ Munteanu et al. evaluated the regioselectivity of microwave-assisted Cu(I)-catalyzed cycloaddition between azido and alkyne groups.¹⁷ Owing to its advantages, this efficient method has been tremendously employed in the fields of combinatorial chemistry,¹⁸ materials science,^19–21 and surface modification.²² In the field of chromatographic applications, Zhang et al. reported the preparation of a clicked chiral stationary phase (CSP) for high performance liquid chromatography (HPLC) enantioseparations.²³ Wang et al. also developed clicked CD-based CSP for enantioseparation in HPLC.²⁴ A CD-derived macroporous organic polymer monolith has also been developed via the click approach for chiral capillary electrochromatography (CEC) and nano-LC.²⁵

In this context, few researchers have explored the development of clicked CD derivatives as a mobile phase for enantioseparation in CE. In our earlier systematical work, we have developed a library of mono-alkylimidazolium CDs and AC-disubstituted CDs bearing both alkylimidazolium and ammonium cationic sites.^26–29 On the basis of practical experience, the validation of CE methods using cationic CDs was difficult to achieve because of the strong tendency of CDs to adsorb onto the capillary wall, resulting in irreproducible EOF and analyte migration times.³⁰ Despite this drawback, the cationic CDs were suitable for resolving acidic racemates by taking the advantage of electrostatic interactions. Furthermore, the presence of the imidazolium ring was demonstrated to be beneficial to the enantioseparation of dansyl amino acids because of the formation of π–π conjunctions between the imidazole moiety of the CDs and the aromatic moieties of the analytes.³¹

In view of the good enantioselectivities of AC regioisomer diamino-β-cyclodextrins³² and hydroxyalkylammonium³³ for the enantioseparation of carboxylic acids, we were intrigued by the possibility of developing efficient AC regioisomers with imidazolium functionality via click chemistry for the enantioseparation of amino acids. Herein, we propose the synthesis of clicked AC regioisomer CDs for chiral recognition. The click synthesis of 6^A-2-hydroxyalkyl-1,2,3-triazole-6^C-methoxyalkylimidazolium-β-CD chloride is depicted in Scheme 1. With the clicked AC regioisomer cationic CDs at hand, their molecular level chiral recognition ability as chiral selectors in CE was evaluated.

Scheme 1 Synthetic route of 6^A-2-hydroxyethyl-1,2,3-triazole-6^C-methoxyalkylimidazolium-β-CD chlorides.

As described in Scheme 1, the three-step synthesis of disubstituted CDs started with an important AC regioisomer CD intermediate, 6^A-azido-6^C-mesitylene-sulfonyl-β-cyclodextrin (Mess-N₃-CD, 3), which was readily obtained according to our previous protocol.^27,28 A further nucleophilic addition between 3 and methoxyalkylimidazole successfully introduced the imidazolium cation to the C6 position at the CD primary rim. A crucial azide/alkyne 1,3-cycloaddition (click chemistry) reaction using an organic soluble Cu catalyst afforded 6^A-2-hydroxyalkyl-1,2,3-triazole-6^C-methoxyalkylimidazolium-β-CD mesitylene sulfonate 6 in ∼75% yield. The title product 7 was obtained through anionic exchange with Amberlite (Cl) resin.

By varying the alkyl chain length of the methoxyalkylimidazole, two clicked AC regioisomer cationic CDs were synthesized. All of them exhibit good enantioselectivities towards negatively charged racemates. Herein, we took 6^A-4-hydroxyethyl-1,2,3-triazole-6^C-3-methoxypropylimidazolium-β-cyclodextrin chloride (7b) as an example to illustrate the enantioseparation capability of the synthesized CDs in chiral CE. A series of Dns-amino acids and acidic enantiomers (see Fig. 1) was selected as model analytes to evaluate the chiral recognition ability of the clicked AC regioisomer CDs.

Fig. 1 Structures of racemic analytes used in current study.

In a run of CE separation, the transportation of analytes is primarily due to electroosmotic flow (EOF), which originates from the electrical layer formed on the inter surface of the capillary.³⁴ Each sample run was performed in triplicate to guarantee good reproducibility. Three pH values of buffer were applied to evaluate elution behaviour changes with 5.0 mM CD. As summarized in Table 1, low pH led to longer elution time because of the suppressive dissociation of silanol groups.

Table 1 Effect of buffer pH on chiral separations of selected analytes with 5.0 mM CD

Analytes	pH = 5.0			pH = 6.0			pH = 7.0
	t2	α	Rs	t2	α	Rs	t2	α	Rs
Dns-Aca	29.21	1.03	2.1	28.50	1.04	2.2	19.04	1.02	1.7
Dns-Met	24.98	1.01	1.1	24.23	1.02	1.2	20.14	1.01	1.4
Dns-Thr	27.95	1.02	1.8	26.80	1.08	5.7	19.92	1.05	3.3
Dns-Phe	24.58	1.03	2.3	23.15	1.06	2.6	18.32	1.03	1.8
Dns-Aba	24.78	1.03	2.7	23.12	1.06	2.5	16.06	1.02	1.7
Dns-Ser	31.58	1.02	1.5	29.97	1.04	1.5	16.83	1.01	1.2
Dns-Nva	26.75	1.02	1.7	24.40	1.02	0.7	16.83	1.02	1.1
pHyPAA	30.23	1.02	2.0	31.29	1.14	5.28	17.64	1.04	2.7
PCPAA	20.42	1.01	1.3	17.43	1.03	3.5	12.93	1.03	2.5
CHPAA	25.78	1.05	2.5	25.30	1.09	2.7	17.83	1.02	2.1

---

In the present study, a pH value of 6.0 seemed to be the best choice for all the analytes in terms of selectivity, affording the highest α values. For Dns-Thr, the selectivities were 1.02, 1.08 and 1.05 with increased pH buffer. Moreover, the maximum peak resolutions were achieved at pH 6.0 for all racemates except Dns-Aba and Dns-Nva. It is noteworthy that peak resolutions were 1.7, 0.7 and 1.1 in the case of Dns-Nva.

All the analytes were well resolved under optimized conditions using this CD. Consistent positive EOF was generated after a voltage was applied, which indicated that the triazole linkage did not affect the orientation of the EOF even though the linkage can be cationic charged. As shown in Table 2, the best enantioseparations were achieved at 5 mM CD for most racemates. In general, the high concentrations of cationic CDs in buffer resulted in longer elution because of the more significant adsorption at the interface wall of the capillary compared with ionic or neutral CDs. For example, the elution time of Dns-Met was only 17.2 min at 2.5 mM, while it was extended to 28.0 min at 10 mM CD. It was exceptional that the migration time of Dns-Ser obtained at 5 mM was slightly shorter than that at lower CD concentrations. Compared with our previous reported AC-dicationic CDs,^27,28 this CD could realize satisfactory enantioseparation with shorter analysis time (ca. ≤30 min). For most cases, baseline separations (α > 1.01 and R_s > 1.5) were realized at pH 6.0 though several analytes could not be resolved at 1.0 mM CD. The peak resolutions for Dns-Thr and pHyPAA reached over 5.0 with 5.0 mM CD, whilst the selectivities were 1.01, 1.05, 1.14 and 1.03 from low to high concentration, respectively. Dns-Phe and PCPAA were well resolved even at 1.0 mM CD. Representative electrophoretograms for selected racemates are depicted in Fig. 2.

Table 2 Migration time (t₂ min⁻¹) of the second enantiomer, selectivity (α) and peak resolution (R_s) of analytes with different CD concentrations in pH 6.0 BGEs

Analytes	2.5 mM			5 mM			10 mM
	t2	A	Rs	t2	α	Rs	t2	α	Rs
Dns-Aca	20.60	1.02	0.8	28.50	1.04	2.2	26.98	1.01	0.9
Dns-Met	17.23	1.01	0.33	24.23	1.02	1.2	28.01	1.01	0.8
Dns-Thr	24.15	1.03	0.9	26.80	1.08	5.7	26.30	1.06	2.9
Dns-Phe	19.58	1.05	1.1	23.15	1.06	2.6	20.87	1.02	2.1
Dns-Aba	22.58	1.06	1.0	23.12	1.06	2.5	25.05	1.04	1.9
Dns-Ser	29.67	1.02	0.8	29.97	1.04	1.5	31.84	1.00	0.6
Dns-Nva	18.41	1.08	2.4	24.40	1.02	0.7	28.30	1.02	0.8
pHyPAA	21.57	1.05	2.4	31.29	1.14	5.3	30.12	1.03	1.6
PCPAA	17.27	1.03	1.3	17.43	1.03	3.5	21.05	1.04	2.3
CHPAA	12.12	1.02	0.9	25.30	1.09	2.7	24.50	1.03	1.2

---

Fig. 2 Representative electrophoretograms of CE separations. Conditions: 50 mM phosphate buffer with pH of 6.0; injection: 3.45 kPa for 5 s; voltage: 15 kV; detection: 214 nm.

In summary, we have explored click chemistry in the preparation of AC regioisomer cationic CDs. The CDs demonstrated moderate enantioselectivity towards ampholytic and acid racemates in CE. The highest selectivities and peak resolutions for most analytes were observed with 5.0 mM CD at pH 6.0 BGEs. Baseline enantioseparation of analytes could be achieved even at 1.0 mM CD. Further investigations of the recognition mechanism, especially the hydrogen bonding and π–π conjunctions, remain to be conducted. Nevertheless, a promising approach for the exploration of clicked CD derivatives is presented for aqueous processes such as chiral CE and catalysis.

Experimental section

CE separations were performed on a P/ACE MDQ system (Fullerton, CA, USA), equipped with an online photodiode array (PDA) detector. NMR spectroscopy measurements were performed on a Bruker AVANCE 500 (500 MHz, Bruker Daltonics, Bremen, Germany). FT-IR characterization was achieved on a Bomen MB154S. All the racemates were purchased from Sigma (St. Louis, MO, USA), with β-CD obtained from Tokyo Chemical Industry (TCI, Japan). All the other chemicals were procured from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China) and used without further purification unless stated. The buffers for CE separation were prepared by dissolving NaH₂PO₄ in ultra-pure water and adjusted to the desired pH value. All mobile phases were freshly prepared and degassed prior to use. Mess-N₃-CD was prepared according to our previous report.²⁸

Methoxyalkylimidazole 2

Sodium hydride (3.0 g, 125 mmol) was added to a two neck round-bottom flask under N₂ atmosphere. Hexane was used to remove the paraffin. DMF (30 mL) was added to dissolve sodium hydride in an ice bath for 10 min. Then, imidazole solution (9.2 g, 120 mmol) dissolved in DMF (30 mL) was slowly added. Afterwards, 1-bromo-2-methoxyethane (16.68 g, 120 mmol) or 1-bromo-3-methoxypropane (18.36 g, 120 mmol) was injected using a syringe before overnight refluxing the reaction at 90 °C. The filtrate was extracted using CH₂Cl₂. The organic layer was evaporated to yield the product as a brown liquid.

2-Methoxyethylimidazole 2a (11.75 g, 68.9%)

¹H NMR (500 MHz, DMSO-d₆) δ: 8.13 (s, 1H, =CH_2im), 7.77 (s, 1H, =CH_5im), 7.62 (s, 1H, =CH_4im), 4.33 (t, 2H, –CH_2-im), 3.85 (t, 2H, –CH_2-OCH3), 3.30 (s, 3H, –OCH₃); ¹³C NMR (125 MHz, DMSO-d₆), 131.5 (C_2im), 122.9 (C_4im), 126.6 (C_5im), 74.1 (CH_2-OCH3), 59.5 (–OCH₃), 48.7 (CH_2-im).

3-Methoxypropylimidazole 2b (13.5 g, 71.2%)

¹H NMR (500 MHz, DMSO-d₆) δ: 8.13 (s, 1H, =CH_2im), 7.77 (s, 1H, =CH_5im), 7.64 (s, 1H, =CH_4im), 3.98 (s, 2H, –CH_2-im), 3.57 (t, 2H, –CH_2-OCH3), 3.30 (s, 3H, –OCH₃), 1.94 (m, 2H, –CH₂); ¹³C NMR (125 MHz, DMSO-d₆) δ: 132.8 (C_2im), 122.9 (C_4im), 126.6 (C_5im), 68.9 (CH_2-OCH3), 59.3 (–OCH₃), 46.2 (CH_2-im), 30.6 (CH₂).

6^A-Azido-6^C-methoxyalkylimidazolium-β-cyclodextrin mesitylene sulfonate 5

Under the protection of nitrogen, the reaction mixture of 3 (2.2 mmol, 3.0 g) and methoxyalkylimidazole (2a, 0.83 g, 6.6 mmol; 2b, 0.93 g, 6.6 mmol) in dry DMF (15 mL) was heated at 90 °C under vigorous stirring for 2 days. After cooling to room temperature, the reaction mixture was poured into acetone (100 mL). The crude product was filtered and washed with acetone (2 × 250 mL) before drying at 50 °C under vacuum. After recrystallization from water, the product 5 was obtained as a white solid.

6^A-Azido-6^C-2-methoxyethylimidazolium-β-cyclodextrin mesitylene sulfonate 5a (2.78 g, 86%)

¹H NMR (500 MHz, DMSO-d₆) δ: 9.13 (s, 1H, =CH_2im), 7.94 (s, 1H, =CH_5im), 7.77 (s, 1H, =CH_4im), 7.71 (s, 1H, =CH_4im), 7.34 (s, 2H, =CH), 5.96–5.69 (m, 14H, OH-2 and OH-3), 4.95–4.82 (m, 7H, H-1), 4.51–4.58 (m, 5H, OH-6), 4.21 (m, 2H, –CH_2-im), 3.95 (m, 2H, CH_2-OCH3), 3.64–3.49 (m, 26H, H-5, H-3 and H-6), 3.35–3.29 (m, 14H, H-2 and H-4), 3.21 (s, 3H, –OCH₃), 2.43 (s, 6H, –CH_3-o-OMess), 2.17 (s, 3H, –CH_3-p-OMess); ¹³C NMR (125 MHz, DMSO-d₆) 142.0 (Cipso), 136.2 (C_o-OMess), 136.1 (C_p-OMess), 129.7 (C_m-OMess), 129.51 (C_2im), 122.96 (C_4im), 126.61 (C_5im), 101.7 (C1), 81.5 (C4), 73.3 (CH_2-OCH3), 72.70 (C2), 72.1 (C3), 71.8 (C3′), 71.6 (C5), 59.67 (C6), 59.3 (OCH₃), 49.30 (CH_2-im), 22.30 (CH_3-o-OMess), 20.41(CH_3-p-OMess). FT-IR (cm⁻¹, KBr): 3300 (O–H str), 2917 (C–H stre), 2102 (N≡N str), 1670 (C=C str), 1367 (C–N str), 1143 (S=O str), 1012 (C–O–C stretch).

6^A-Azido-6^C-3-methoxypropylimidazolium-β-cyclodextrin mesitylene sulfonate 5b (2.8 g, 83%)

¹H NMR (500 MHz, DMSO-d₆) δ: 9.12 (s, 1H, =CH_2im), 7.78 (s, 1H, =CH_5im), 7.72 (s, 1H, =CH_4im), 7.37 (s, 2H, =CH), 5.94–5.64 (m, 14H, OH-2 and OH-3), 4.97–4.79 (m, 7H, H-1), 4.63–4.57 (m, 5H, OH-6), 4.21 (m, 2H, –CH_2-im), 3.87 (m, 2H, CH_2-OCH3), 3.62–3.47 (m, 26H, H-5, H-3 and H-6), 3.33–3.30 (m, 14H, H-2 and H-4), 3.22 (s, 3H, –OCH3), 2.69 (m, 2H, CH₂), 2.45 (s, 6H, –CH_3-o-OMess), 2.25 (s, 3H, –CH_3-p-OMess); ¹³C NMR (125 MHz, DMSO-d₆) δ: 142.1 (Cipso), 136.4 (C_o-OMess), 135.9 (C_p-OMess), 129.8 (C_m-OMess), 128.4 (C_2im), 127.3 (C_4im), 126.4 (C_5im), 102.7 (C1), 82.9 (C4), 73.2 (C2), 72.9(CH_2-OCH3), 72.69 (C3), 68.2 (C5), 60.6 (CH_2-OH), 60.5 (C6), 58.4 (OCH₃), 48.65 (CH_2-im), 29.7 (CH₂), 22.8 (CH₃-o-OMess), 19.5 (CH₃-p-OMess); FT-IR (cm⁻¹, KBr): 3300 (O–H str), 2917 (C–H str), 2102 (N≡N str), 1668 (C=C str), 1387 (C–N str), 1143 (S=O str), 1013 (C–O–C str).

6^A-4-Hydroxyethyl-1,2,3-triazole-6^C-methoxyalkylimidazolium-β-cyclodextrin mesitylene sulfonate 6

A mixture of 5 (5a, 1.45 g, 1.0 mmol; 5b, 1.48 g, 1.0 mmol), cuprous iodide triphenylphosphine (60 mg, 0.1 mmol), 3-butyn-1-ol (0.076 mL, 1.2 mmol) and DMF (15 mL) was refluxed at 90 °C for 1 day. The reaction mixture was poured into acetone to precipitate the crude product. The title product 6 was recrystallized two times from water to afford a white solid.

6^A-4-Hydroxyethyl-1,2,3-triazole-6^C-2-methoxyethylimidazolium-β-cyclodextrin mesitylene sulfonate 6a (1.2 g, 79%)

¹H NMR (500 MHz, DMSO-d₆) δ: 9.11 (s, 1H, =CH_2im), 7.93 (s, 1H, =CH), 7.77 (s, 1H, =CH_5im), 7.71 (s, 1H, =CH_4im), 7.37 (s, 2H, CH_ben), 6.02–5.74 (m, 14H, OH-2 and OH-3), 5.04–4.82 (m, 7H, H-1), 4.58–4.51 (m, 5H, OH-6), 4.21 (m, 2H, –CH_2-im), 3.95 (m, 2H, CH_2-OCH3), 3.64–3.49 (m, 26H, H-5, H-3 and H-6), 3.35–3.23 (m, 14H, H-2 and H-4), 3.17 (s, 3H, –OCH₃), 2.88 (t, 2H, CH_2-OH), 2.74–2.72 (t, 2H, CH₂), 2.40 (s, 6H, –CH_3-o-OMess), 2.25 (s, 3H, –CH_3-p-OMess); ¹³C NMR (125 MHz, DMSO-d₆) δ: 142.0 (C_ipso),136.2 (C_o-OMess), 136.0 (C_p-OMess), 129.7 (C_meta-OMess), 137.8 (=C_2im), 131.50 (C–N), 130.70 (=C_4im), 128.44 (=C_5im), 123.2 (CH–N), 102.9 (C1), 83.9 (C4), 73.2 (C2), 73.0 (CH_2-OCH3), 71.9 (C3), 72.6 (C5), 68.1 (C5′), 60.5 (C6), 60.8 (CH_2-OH), 58.5 (OCH₃), 48.65 (CH_2-im), 29.70 (CH_2-CN), 22.3 (CH_{3-ortho-OMess}), 20.4 (CH_3-para-OMess); FT-IR (cm⁻¹, KBr): 3311 (O–H str), 2927 (C–H str), 1637 (C=C str), 1333 (C–N str), 1157 (N=N str),1020 (C–O–C str).

6^A-4-Hydroxyethyl-1,2,3-triazole-6^C-2-methoxyethylimidazolium-β-cyclodextrin mesitylene sulfonate 6b (1.2 g, 75%)

¹H NMR (500 MHz, DMSO-d₆) δ: 9.12 (s, 1H, =CH_2im), 7.94 (s, 1H, =CH), 7.78 (s, 1H, =CH_5im), 7.72 (s, 1H, =CH_4im), 7.33 (s, 2H, CH_ben), 6.01–5.73 (m, 14H, OH-2 and OH-3), 5.16–4.98 (m, 7H, H-1), 4.58–4.51 (m, 5H, OH-6), 4.21 (m, 2H, –CH_2-im), 3.95 (m, 2H, CH_2-OCH3), 3.64–3.49 (m, 26H, H-5, H-3 and H-6), 3.35–3.23 (m, 14H, H-2 and H-4), 3.17 (s, 3H, –OCH₃), 2.88 (t, 2H, CH_2-OH), 2.74–2.72 (t, 2H, CH₂), 2.65 (m, 2H, CH₂), 2.36 (s, 6H, –CH_3-o-OMess), 2.24 (s, 3H, –CH_3-p-OMess); ¹³C NMR (125 MHz, DMSO-d₆) δ: 142.3 (C_ipso), 136.2 (C_o-OMess), 136.1 (C_p-OMess), 129.7 (C_m-OMess), 137.8 (C_2im), 131.5 (C–N), 130.9 (C_4im), 128.4 (C_5im), 123.20 (CH–N), 102.9 (C1), 84.5 (C4), 73.2 (C2), 73.00 (CH_2-OCH3), 71.9 (C3), 72.6 (C5), 68.1 (C5′), 60.5 (C6), 60.80 (CH_2-OH), 48.7 (CH_2-im), 27.4 (CH_2-CN), 22.6 (CH_3-o-OMess), 19.8 (CH_3-p-OMess); FT-IR (cm⁻¹, KBr): 3311 (O–H str), 2927 (C–H str), 1643 (C=C str), 1333(C–N stre), 1161 (N=N str), 1012 (C–O–C str).

6^A-4-Hydroxyethyl-1,2,3-triazole-6^C-methoxyalkylimidazolium-β-cyclodextrin chloride 7

An aqueous solution of 6a (1.0 g, 0.66 mmol) or 6b (1.0 g, 0.65 mmol) was immersed into a column filled with Amberlite IRA-900 ion-exchange resin for 12 h. The eluent was collected and evaporated to afford the title product 7 as a white solid.

6^A-4-Hydroxyethyl-1,2,3-triazole-6^C-2-methoxyethylimidazolium-β-cyclodextrin chloride 7a (0.85 g, 94%)

¹H NMR (500 MHz, DMSO-d₆) δ: 9.11 (s, 1H, =CH_2im), 7.93 (s, 1H, =CH), 7.77 (s, 1H, =CH_5im), 7.71 (s, 1H, =CH_4im), 5.96–5.69 (m, 14H, OH-2 and OH-3), 4.95–4.82 (m, 7H, H-1), 4.58–4.51 (m, 5H, OH-6), 4.21 (m, 2H, –CH_2-im), 3.95 (m, 2H, CH_2-OCH3), 3.64–3.49 (m, 26H, H-5, H-3 and H-6), 3.35–3.29 (m, 14H, H-2 and H-4), 3.21 (s, 3H, –OCH₃), 2.88 (t, 2H, CH_2-OH), 2.74–2.72 (t, 2H, CH₂); ¹³C NMR (125 MHz, DMSO-d₆) δ: 137.8 (C_2im), 131.5 (C–N), 130.7 (C_4im), 128.4 (C_5im), 123.2 (=CH–N), 102.9 (C1), 83.6 (C4), 73.2 (C2), 73.0 (CH_2-OCH3), 71.9 (C3), 72.5 (C5), 68.1 (C5′), 60.8 (CH_2-OH) 60.52 (C6), 58.5 (OCH₃), 48.6 (CH_2-im), 29.7 (CH_2-CN); IR (cm⁻¹, KBr): 3311 (O–H str), 2927 (C–H str), 1637 (C=C str), 1333 (C–N str), 1157 (N=N str), 1020 (C–O–C str).

6^A-4-Hydroxyethyl-1,2,3-triazole-6^C-3-methoxypropylimidazolium-β-cyclodextrin chloride 7b (0.8 g, 90%)

¹H NMR (500 MHz, DMSO-d₆) δ: 9.12 (s, 1H, =CH_2im), 7.93 (s, 1H, =CH), 7.78 (s, 1H, =CH_5im), 7.72 (s, 1H, =CH_4im), 5.94–5.64 (m, 14H, OH-2 and OH-3), 4.97–4.79 (m, 7H, H-1), 4.63–4.57 (m, 5H, OH-6), 4.23 (m, 2H, –CH_2-im), 3.97 (m, 2H, CH_2-OCH3), 3.64–3.50 (m, 26H, H-5, H-3 and H-6), 3.36–3.30 (m, 14H, H-2 and H-4), 3.25 (s, 3H, –OCH₃), 2.89 (t, 2H, CH_2-OH), 2.74–2.72 (t, 2H, CH₂), 2.65 (m, 2H, CH₂); ¹³C NMR (125 MHz, DMSO-d₆) δ: 137.4 (C_2im), 131.5 (C–N), 130.7 (C_4im), 128.4 (C_5im), 123.7 (=CH–N), 102.7 (C1), 83.9 (C4), 73.2 (C2), 73.1 (CH_2-OCH3), 72.69 (C3), 68.2 (C5), 60.6 (CH_2-OH), 60.5 (C6), 58.4 (OCH₃), 48.65 (CH_2-im), 30.6 (CH_2-CN), 29.7 (CH₂); FT-IR (cm⁻¹, KBr): 3311 (O–H str), 2927 (C–H str), 1643 (C=C str), 1333 (C–N str), 1161 (N=N str), 1012 (C–O–C str).

References

1. T. J. Ward and K. D. Ward, Anal. Chem., 2010, 82, 4712.
2. S. E. Deeb, H. Watzig, D. A. EI-Hady, H. M. Albishri, C. S. D. Griend and G. K. E. Scriba, Electrophoresis, 2014, 35, 170.
3. L. Suntornsuk, Anal. Bioanal. Chem., 2010, 398, 29–52.
4. M. Pioch, S. C. Bunz and C. Neusüβ, Electrophoresis, 2012, 33, 1517.
5. R. Fang, L.-X. Yi, Y.-X. Shao, L. Zhang and G.-H. Chen, J. Liq. Chromatogr. Relat. Technol., 2014, 37, 1465.
6. A. Stalmach, A. Albalat, W. Mullen and H. Mischak, Electrophoresis, 2013, 34, 1452.
7. A. Latosinska, M. Frantzi, A. Vlahou and H. Mischak, Proteomics: Clin. Appl., 2013, 7, 779.
8. C. Desiderio, D. V. Rossetti, F. Iavarone, I. Messana and M. Castagnola, J. Pharm. Biomed. Anal., 2010, 53, 1161.
9. A. B. Bergamo, J. A. F. d. Silva and D. P. d. Jesus, Food Chem., 2011, 124, 1714.
10. M. Herrero, G.-C. Virginia, S. Carolina and C. Alejandro, Electrophoresis, 2010, 31, 205.
11. S. Fanali, Electrophoresis, 2009, 30, S203.
12. W. Tang and S. C. Ng, Nat. Protoc., 2008, 3, 691.
13. V. Cucinotta, A. Contino, A. Giuffrida, G. Maccarrone and M. Messina, J. Chromatogr. A, 2010, 1217, 953.
14. Y. Dai, S. Wang, J. Zhou, Y. Liu, D. Sun, J. Tang and W. Tang, J. Chromatogr. A, 2012, 1246, 98.
15. H. C. Kolb, M. G. Finn and K. B. Sharpless, Angew. Chem., Int. Ed., 2001, 40, 2004.
16. V. O. Rodionov, V. V. Fokin and M. Finn, Angew. Chem., Int. Ed., 2005, 117, 2250.
17. M. Munteanu, S. W. Choi and H. Ritter, Marcomolecules, 2008, 41, 5.
18. W.-C. Cheng, C.-Y. Weng, W.-Y. Yun, S.-Y. Chang, Y.-C. Lin, F.-J. Tsai, F.-Y. Huang and Y.-R. Chen, Bioorg. Med. Chem., 2013, 21, 5021.
19. H. Nandivada, X. Jiang and J. Lahann, Adv. Mater., 2007, 19, 2197.
20. W. H. Binder and R. Sachsenhofer, Macromol. Rapid Commun., 2008, 29, 952.
21. R. Kluger, J. Am. Chem. Soc., 2010, 132, 6611.
22. A. Hayat, A. Sassolas, J.-L. Marty and A.-E. Radi, Talanta, 2013, 103, 14.
23. S. Zhang, H. Wang, J. Tang, W. Wang and W. Tang, Anal. Methods, 2014, 6, 2034.
24. Y. Wang, D. J. Young, T. T. Tan and S. C. Ng, J. Chromatogr. A, 2010, 1217, 7878.
25. M. Guerrouache, M. C. Millot and B. Carbonnier, Macromol. Rapid Commun., 2009, 30, 109.
26. W. Tang, I. W. Muderawan, T. T. Ong and S. C. Ng, Electrophoresis, 2005, 26, 3125.
27. Y. Dai, S. Wang, J. Wu, J. Tang and W. Tang, RSC Adv., 2012, 2, 12652.
28. Y. Dai, S. Wang, J. Zhou, J. Tang and W. Tang, Electrophoresis, 2013, 34, 833.
29. W. Tang, T. T. Ong and S. C. Ng, J. Sep. Sci., 2007, 30, 1343.
30. V. Cucinotta, A. Contino, A. Giuffrida, G. Maccarrone and M. Messina, J. Chromatogr. A, 2010, 1217, 953.
31. J. Tang, Y. Lu, Y. Wang, J. Zhou and W. Tang, Talanta, 2014, 128, 460.
32. G. Galaverna, M. C. Paganuzzi, R. Corradini, A. Dossena and R. Marchelli, Electrophoresis, 2001, 22, 3171.
33. J. Zhou, F. Ai, B. Zhou, J. Tang, S. C. Ng and W. Tang, Anal. Chim. Acta, 2013, 800, 95.
34. M. Lämmerhofer, F. Svec, J. M. Fréchet and W. Lindner, TrAC, Trends Anal. Chem., 2000, 19, 676.

---