A Novel and Practical Synthesis of Isavuconazonium Sulfate via Anion Exchange Resin

Abstract

In this study, an efficient and practical process for the synthesis of isavuconazonium sulfate (compound 1), an antifungal agent, was described. Highlights in the synthesis route are the usage of the ion exchange resin instead of H₂SO₄ to introduce the HSO₄ ⁻ anion in the formulation of quaternary ammonium salt (1), and the reaction condition was further optimized to facilitate the scale-up. The overall yield of the process was 57.0% and the high-performance liquid chromatography purity of product was 97.25%, which was higher than that of the reference-listed drug.

Keywords

isavuconazonium sulfate - synthesis - anion exchange resin

Introduction

Isavuconazonium sulfate (1) is a prodrug of isavuconazole (2), which is a broad-spectrum triazole antifungal agent and widely used for the treatment of invasive fungal infections.[1] [2] [3] [4] [5] [6] [7] The water-soluble compound 1 includes a triazolium salt tethered to isavuconazole via an ester moiety ([Fig. 1]). Evidence suggested that many antifungal drugs, such as itraconazole and voriconazole, often used cyclodextrin vehicle, to facilitate the solubility in their intravenous formulation, yet had been speculated to be nephrotoxic in humans.[8] Inspiringly, compound 1 does not require a cyclodextrin vehicle due to its natural water-soluble nature, and thereby can represent a better option in the therapy of fungal infections in comparison to other triazole antifungal agents.[8] [9] [10]

Fig. 1 Structures of isavuconazonium sulfate (1) and isavuconazole (2).

The current two reported approaches for the synthesis of compound 1 are described in [Scheme 1]. The original preparation of compound 1 was based on Fukuda et al's method using isavuconazonium chloride hydrochloride rather than bisulfate as the key intermediate.[11] Later, Zhou et al reported a new synthetic route in 2017, directly using CuSO₄ to introduce SO₄ ²⁻ to the triazolium salt.[12] The generated key intermediate (7) was acidified by H₂SO₄ to obtain the target compound. However, these routes had three shortcomings: first, compound 5 degraded a lot owing to basic ion exchange resin in the preparation of compound 6. Second, due to multiple alkaline sites in isavuconazonium, it is difficult to form the HSO₄ ⁻ salt of isavuconazonium in a 1:1 ratio through directly adding H₂SO₄. Finally, both the reported two routes suffered from purification problems due to the thermal instability of the target product. Thus, developing a method for preparing compound 1 with a high yield and purity is necessary.

Scheme 1 Reported synthetic routes of isavuconazonium sulfate (1) by Fukuda et al's method (Route 1) and Zhou et al's method (Route 2).

In this study, we first report a novel synthetic route ([Scheme 2]), wherein compound 5 was obtained according to Fukuda et al's method (Route 1 in [Scheme 1]), then neutralized in basic solution to give compound 6. The OH⁻ anion of compound 6 was ion exchanged by HSO₄ ⁻ from resin loaded with HSO₄ ⁻ to form the target compound 1.

Scheme 2 New synthetic route via ion exchange resin reported by this work.

Results and Discussion

Improved Synthesis of Key Intermediate 4 and the underlying Mechanism

Fukuda et al used a catalytic amount of NaI to prepare key intermediate 4 (Route 1 in [Scheme 1]).[1] However, the yield was too low to be acceptable when the ratio of NaI was below 30% ([Table 1], entries 1–9). Interestingly, this work found that higher equivalents of NaI afforded higher yields of 4 ([Table 1], entries 7–12), and when 1.1 equivalent of NaI was added ([Table 1], entries 12 and 13), compound 2 was reacted completely, indicating that NaI may take a part in the reaction rather than acting as a catalyst. A possible reaction mechanism is proposed in [Scheme 3].

Table 1 Optimization of conditions for the forming of intermediate 4

Entry	Solvent	Temp (°C)	Time (h)	NaI (mol%)	Yield (%)
1	THF	70	3	0.1	10.0
2	Acetone	70	3	0.1	9.7
3	CH3CN	70	3	0.1	9.9
4	CH3CN	50	3	0.1	9.9
5	CH3CN	90	3	0.1	9.8
6	CH3CN	70	5	0.1	9.9
7	CH3CN	70	7	0.1	9.7
8	CH3CN	70	3	20	19.4
9	CH3CN	70	3	30	31.0
10	CH3CN	70	3	50	44.2
11	CH3CN	70	3	90	80.4
12	CH3CN	70	3	110	95.6
13	CH3CN	70	3	130	95.2

Scheme 3 Proposed mechanism for the synthesis of isavuconazonium iodide 4.

Preparation of Compound 6

Removing the Boc of compound 4 in HCl (aq) solution obtained compound 5, and the I⁻ of which was replaced with OH⁻ to obtain compound 6. Fukuda et al used an ion-exchange resin to introduce OH⁻. However, under basic conditions, the ester groups in compound 5 were easy to hydrolyze, and the hydrolyzed products (2, 8, 9) are shown in [Scheme 4]. Even if compound 5 was suspended in 5% NaHCO₃ solution and extracted with dichloromethane (DCM), the hydrolysis of compound 5 was still unstoppable. In this work, the process of obtaining compound 6 was improved. Compound 5 was added into a two-phase DCM/water solvent system at a low temperature, followed by HCl neutralization and the replacement of I⁻ with OH⁻ under basic conditions. The generated compound 6 was immediately transferred into an organic phase, thus avoiding degradation. This solution was used for the next step without further work-up.

Scheme 4 Degradation mechanism of compound 5 under basic conditions.

Preparation of Target Compound 1 (Isavuconazonium Sulfate)

To obtain the target compound 1, Fukuda et al replaced the OH⁻ group of compound 6 with HSO₄ ⁻ by addition of H₂SO₄. However, it was found that when H₂SO₄ was added to the reaction mixture, compound 6 was degraded into impurity 8 and isavuconazole (2), and the product precipitated as a syrup, which could not be purified because of its poor solid form and thermal instability. Given above, the introduction of HSO₄ ⁻ anion via a medium that would provide a pure convenient ion pair is significantly important.

Evidence suggested that some I⁻-containing imidazolium ionic liquids can be anion-exchanged with anion–exchange resin loaded with different anions.[13] Considering that isavuconazonium has a similar quaternary ammonium moiety to these imidazolium ionic liquids, we used the anion-exchange resin loading with HSO₄ ⁻ as a medium for the introduction of HSO₄ ⁻ into isavuconazonium, and the ion-exchange reaction is described in [Scheme 5]. Our explored method thereby achieved better outcomes compared with the use of H₂SO₄ (aq) solution.

Scheme 5 Ion exchange between ionic compound and the specific resin.

The conditions for the ion-exchange reaction were also explored. Initially, a strongly basic anion-exchange resin Amberlyst A-26 (OH⁻ form) was used. The resin was treated with ammonium hydrogen sulfate (NH₄HSO₄) solution to retain HSO₄ ⁻ in the resin. The solution of compound 6 in DCM was concentrated and the residue was re-dissolved in methanol and stirred with A-26 resin (HSO₄ ⁻ form) according to a reported study.[13] However, the reaction outcome was disappointing, with a formation of a complex product mixture. We assumed that the concentration process may contribute to the degradation of isavuconazonium, because compound 6 was thermally sensitive in solution. Besides, an additional stability experiment also indicated that compound 1 was unstable in methanol. Therefore, DCM solution of compound 6 was moved to the next procedure directly instead of using after concentration. Ion exchange was performed directly using DCM solution of compound 6, unfortunately, the residue was found again to contain a complex mixture, which was hard to be purified.

Then, a biphasic system was trialed in this step. The approach was based on the excellent water solubility of the expected product, with the expectation that performing anion exchange in a biphasic system would partition the targeted water-soluble products (mostly generated from the coordination of isavuconazonium with HSO₄ ⁻ in the aqueous phase), and the lipophilic impurities were reserved in the organic phase. Excitingly, after the reaction, the resulting aqueous solution was washed with DCM and lyophilized to give the target product in 97.0% purity, without requiring additional purification.

Due to the importance of the anion-exchange resin in this process, three types of commercially available strongly basic anion-exchange resins were screened to compare the resulting product purity and yield. The results indicated that resin Amberlite IRA410 gave the optimal results with a good yield (60.0%) and high-performance liquid chromatography (HPLC) purity (98.03%), as shown in [Table 2].

Table 2 Effect of the type of different resins on the reaction outcome

Entry	Resin type	Yield	HPLC purity
1	D301	24.0%	97.65%
2	IRA402	34.0%	96.70%
3	IRA410	60.0%	98.03%

Abbreviation: HPLC, high-performance liquid chromatography.

Based on this novel and improved process, the batch was scaled up to 100 g and the results were reproduced in three validation productions. Furthermore, results from HPLC analysis showed that the peak position of compound 1 was consistent with that of RLD isavuconazonium sulfate for injection, of which the inactive ingredient was mannitol ([Fig. 2]); however, the purity by measuring area percentage of the main peak according to the area normalization method showed that the purity of compound 1 was much higher (97.25%) in comparison to that of RLD isavuconazonium sulfate for injection (94.10%) ([Figs. S6] and [S7] [online only]).

Fig. 2 Overlay map of RLD isavuconazonium sulfate for injection and compound 1 from HPLC analysis. HPLC, high-performance liquid chromatography; RLD, reference listed drug.

Conclusion

In this study, an improved method for the synthesis of isavuconazonium sulfate (1) was reported. An anion-exchange resin was first used to introduce HSO₄ ⁻ to the target compound with the major advantages as the following: (1) only dissociation and ion exchange were mentioned in the new synthetic route, indicating the mild and facile reaction conditions in the whole preparation of the target compound; (2) high HPLC purity (97.25%) of compound 1 was obtained without the need for techniques such as recrystallization and column chromatography; (3) the process met the requirements of “green chemistry” based on the conversion of the starting material isavuconazole, and the overall yield of the synthetic route was 57%; and (4) the used resin could be recycled via acid–base neutralization reactions.

In summary, the novel and practical synthesis of isavuconazonium sulfate (1) was explored in this study, and this may also provide guidance for the synthesis other HSO₄ ⁻ salt analogues in the future. It is a promising reference of application of ion-exchange resins in organic synthesis.

Experimental Section

General

Unless otherwise noted, reagents were commercially available (obtained from Titan, Energy Chemical, Meryer, etc.) and used without purification. NMR data were obtained using a Bruker V-400 instrument (Bruker BioSpin AG, Industriestrasse 26, CH-8117, Fallanden) at 400 MHz for ¹H and 100 Hz for ¹³C in either CDCl₃ or DMSO-d ₆. The chemical shifts are reported in δ ppm relative to tetramethylsilane. HPLC analysis was performed on Agilent 1200 (Agilent Technologies, California, United States) using a Dionex U3000, a Symmetry Shield RP C18 HPLC column (4.6 mm × 250 mm, particle size 5 μm) under the following conditions: mobile A (0.05% TFA aqueous solution) and mobile B (acetonitrile) with gradient condition of 0–17 minutes: mobile A 75%; 17–23 minutes, mobile A 25%, and detection wavelength was 289 nm.

General Procedure to Load HSO₄ ⁻ Anion in Resin IRA410

NH₄HSO₄ aqueous solution (1 mol/L) was passed through a glass column (Shanghai Heqi Glassware Co., Ltd., Shanghai, China) packed with commercial resin IRA410 (OH⁻ form) (Titan) until the pH of the eluent reached the same value as that of the original solution. The process was performed at room temperature using gravity as the driving force.

Preparation of 4-(1-(((3-(((N-(tert-butoxycarbonyl)-N-methylglycyl)oxy)methyl)pyridin-2-yl)(methyl)carbamoyl)oxy)ethyl)-1-((2R,3R)-3-(4-(4-cyanophenyl)thiazol-2-yl)-2-(2,5-difluorophenyl)-2-hydroxybutyl)-1H-1,2,4-triazol-4-ium Iodide (4)

A solution of compound 2 (100 g, 228.83 mmol), sodium iodide (51.5 g, 343.25 mmol), and compound 3 (142.4 g, 343.25 mmol) was stirred in acetonitrile (1,000 mL) for 3 hours at 70°C under a nitrogen atmosphere. The reaction mixture was concentrated under reduced pressure, diluted with ethyl acetate (3 L), and then washed with HCl solution (2%, 1.5 L × 2) and H₂O (1.5 L). The organic layer was dried over MgSO₄, filtered, and the filtrate was evaporated under vacuum to give the crude product 4 as a light-yellow oil (211.7 g, 98% yield). b.p. 86°C (decomposed). ¹H NMR (400 MHz, DMSO-d ₆) δ 10.16 (brd, J = 4.9, 1H), 9.01 (brd, J = 3.6, 1H), 8.49 (s, 1H), 8.24–8.20 (m, 2H), 7.96–7.91 (m, 2H), 7.44–7.26 (m, 6H), 7.15–7.05 (m, 1H), 6.66–6.61 (m, 1H), 6.17–5.90 (m, 2H), 5.76 (s, 2H), 5.09 (d, J = 14.8, 2H), 4.91–4.79 (m, 3H), 4.15 (q, J = 7.3, 1H), 3.15 (s, 1H), 3.12 (s, 2H), 1.99 (s, 3H), 1.42 (s, 9H), 1.20 (d, J = 6.9, 3H). ESI-MS (m/z): calcd. for C₄₀H₄₃F₂IIN₈O₇S [M − I]⁺ 817.2938; found 817.70.

Preparation of 1-((2R,3R)-3-(4-(4-cyanophenyl)thiazol-2-yl)-2-(2,5-difluorophenyl)-2-hydroxybutyl)-4-(1-((methyl(3-(((methylglycyl)oxy)methyl)pyridin-2-yl)carbamoyl)oxy)ethyl)-1H-1,2,4-triazol-4-ium Iodide Hydrochloride (5)

To a solution of compound 4 (211.7 g, 224.25 mmol) in ethyl acetate (1 L) was added hydrogen chloride ethyl acetate solution (2 N, 1121.3 mL) at room temperature. After stirring for 2 hours, the precipitate was filtered and washed with ethyl acetate. The precipitate was dried to afford the crude product 5 as a yellow solid (199.3 g, 97%). b.p. 95°C (decomposed). ¹H NMR (DMSO-d₆ ) δ 10.62–10.35 (m, 1H), 9.39–9.08 (m, 3H), 8.48 (s, 1H), 8.20 (d, J = 7.92 Hz, 2H), 7.99 (d, J = 8.25 Hz, 2H), 7.49–7.02 (m, 5H), 6.84–6.59 (m, 1H), 5.22–4.56 (m, 5H), 4.28–3.79 (m, 2H), 3.30–3.10 (m, 3H), 1.64–1.10 (m, 12H). ESI-MS (m/z): calcd. For C₃₅H₃₅F₂IN₈O₅S [M − I]⁺ 717.2414; found 717.60.

Preparation of 1-((2R,3R)-3-(4-(4-cyanophenyl)thiazol-2-yl)-2-(2,5-difluorophenyl)-2-hydroxybutyl)-4-(1-((methyl(3-(((methylglycyl)oxy)methyl)pyridin-2-yl)carbamoyl)oxy)ethyl)-1H-1,2,4-triazol-4-ium OH⁻ (6)

Compound 5 (199.3 g, 217.5 mmol) was dissolved in a mixture of DCM (1.5 L) and H₂O (500 mL). Then, NaHCO₃ solution (aq, 5%) was slowly added at 0°C until the pH of the mixture was 7.8 to 8.0. The organic layer was separated and maintained at 0°C for the next procedure without further work-up. The product was not isolated and structure conformed.

Preparation of the Target Product (1)

To a solution of the organic layer above (1.5 L) and deionized water (100 mL) was added resin IRA410 (HSO₄ ⁻ form, 1.36 L). The mixture was stirred for 1.5 hours. Water layer was separated, washed with DCM (200 mL × 2), and then lyophilized to give the target compound 1 (106.3 g, 60%) as a white solid. HPLC purity: 97.25%. b.p. 100°C (decomposed); m.p. 143.6–146.2°C. ¹H NMR (400 MHz, D₂O) δ 8.85 (d, J = 30.5 Hz, 1H), 8.66 (s, 1H), 8.44–8.29 (m, 1H), 7.99 (t, J = 7.7 Hz, 1H), 7.89–7.70 (m, 3H), 7.51 (ddd, J = 21.7, 18.0, 6.9 Hz, 3H), 6.87 (ddd, J = 47.0, 19.8, 14.0 Hz, 3H), 5.37–4.99 (m, 3H), 4.99–4.74 (m, 3H), 4.67–4.50 (m, 2H), 4.29–4.10 (m, 1H), 4.01 (d, J = 16.0 Hz, 2H), 3.29–3.06 (m, 3H), 2.80–2.62 (m, 3H), 1.58–1.42 (m, 1H), 1.84 (s, 1H), 1.12 (dd, J = 23.0, 6.9 Hz, 3H). [α]_D ²⁴ +3.505° (c 1.0, H₂O). ¹³C NMR (151 MHz, D₂O) δ 171.76, 166.98, 159.40, 157.79, 155.35, 153.78, 152.95, 151.86, 151.23, 150.70, 149.13, 142.45, 140.19, 137.80, 132.64 (×2), 128.12, 126.45, 125.01, 124.69, 119.15, 117.62, 115.38, 110.06, 79.36, 76.41, 63.04, 59.08, 50.53, 48.63, 43.90, 35.98, 33.00, 19.09, 16.69. ESI-MS (m/z): calcd. For C₃₅H₃₆F₂N₈O₉S₂ [M − HSO₄]⁺ 717.2414; found 717.60.

Supporting Information

Spectroscopic characterization processes (NMR and ESI-MS) for 4 and 1, as well as HPLC results for the purities of compound 1 following the improved synthesis route, are included in the Supporting Information ([Figs. S1–S7] [online only]).

Conflict of Interest

None.

Acknowledgments

We are grateful for the structure conformation provided by Instrumental Analysis and Research Centre of China State Institute of Pharmaceutical Industry.

• References

• 1 Arrieta AC, Neely M, Day JC. et al. Safety, tolerability, and population pharmacokinetics of intravenous and oral isavuconazonium sulfate in pediatric patients. Antimicrob Agents Chemother 2021; 65 (08) e0029021
• 2 Sehgal Vk. Isavuconazonium and resistant fungal infections - a review. World J Pharm Res 2016; 12: 425-429
• 3 Desai A, Kovanda L, Kowalski D, Lu Q, Townsend R, Bonate PL. Population pharmacokinetics of isavuconazole from phase 1 and phase 3 (SECURE) trials in adults and target attainment in patients with invasive infections due to Aspergillus and other filamentous fungi. Antimicrob Agents Chemother 2016; 60 (09) 5483-5491
• 4 Donnelley MA, Zhu ES, Thompson III GR. Isavuconazole in the treatment of invasive aspergillosis and mucormycosis infections. Infect Drug Resist 2016; 9: 79-86
• 5 Pasqualotto AC, Denning DW. New and emerging treatments for fungal infections. J Antimicrob Chemother 2008; 61 (Suppl. 01) i19-i30
• 6 Falci DR, Pasqualotto AC. Profile of isavuconazole and its potential in the treatment of severe invasive fungal infections. Infect Drug Resist 2013; 6: 163-174
• 7 Girmenia C. New generation azole antifungals in clinical investigation. Expert Opin Investig Drugs 2009; 18 (09) 1279-1295
• 8 Livermore J, Hope W. Evaluation of the pharmacokinetics and clinical utility of isavuconazole for treatment of invasive fungal infections. Expert Opin Drug Metab Toxicol 2012; 8 (06) 759-765
• 9 Ohwada J, Tsukazaki M, Hayase T. et al. Design, synthesis and antifungal activity of a novel water soluble prodrug of antifungal triazole. Bioorg Med Chem Lett 2003; 13 (02) 191-196
• 10 Odds FC. Drug evaluation: BAL-8557–a novel broad-spectrum triazole antifungal. Curr Opin Investig Drugs 2006; 7 (08) 766-772
• 11 Fukuda H, Hayase T, Mizuguchi E. N-substituted carbamoyloxyalkyl-azolium derivatives. U.S. Patent 6812238B1. November, 2004
• 12 Zhou WH, Yin QM, Gong RW. et al. Preparation method of isavuconazonium monosulfate through oxidation-reduction reactions [in Chinese]. CN Patent 106916152A. 2017
• 13 Dinarès I, Miguel C, Ibanez A, Mesquida MN, Alcalde E. Imidazolium ionic liquids: a simple anion exchange protocol. Green Chem 2009; 11: 1507-1510

Publikationsverlauf

Eingereicht: 20. Dezember 2021

Angenommen: 25. Februar 2022

Artikel online veröffentlicht:
04. Juli 2022