Process Development of a GCS Inhibitor Including Demonstration of

Subscriber access provided by UNIV OF NEBRASKA - LINCOLN

Full Paper

Process Development of a GCS Inhibitor Including Demonstration of Lossen Rearrangement on Kilogram Scale Jin Zhao, Rayomand Gimi, Sanjeev Katti, Michael Reardon, Vitaly Nivorozhkin, Paul Konowicz, Edward Lee, Lynne M Sole, Jerome Green, and Craig S Siegel Org. Process Res. Dev., Just Accepted Manuscript • DOI: 10.1021/op500379a • Publication Date (Web): 02 Apr 2015 Downloaded from http://pubs.acs.org on April 4, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Organic Process Research & Development is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Organic Process Research & Development

Process Development of a GCS Inhibitor Including Demonstration of Lossen Rearrangement on Kilogram Scale

Jin Zhao,*† Rayomand Gimi, † Sanjeev Katti,# Michael Reardon,‡ Vitaly Nivorozhkin, # Paul Konowicz, ‡ Edward Lee, # Lynne Sole, # Jerome Green, # and Craig S. Siegel *† †

Synthesis Development, Sanofi U.S. R&D, 153 Second Ave, Waltham, MA 02451, U.S.A.

‡

Genzyme, Sanofi U.S. R&D, 270 Albany Street, Cambridge, MA 02193, U.S.A.

#

Members of Chemical Process Development, Genzyme, Waltham, MA, at the time this work

was conducted.

*

Authors to whom correspondences should be sent via email: [email protected],

[email protected]

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 21

ABSTRACT: A small molecule was under investigation as an inhibitor of glucosylceramide synthase (GCS) for potential use in Fabry disease. To support preclinical activities, a 4-step synthesis was developed and used to prepared kilogram quantities of the drug substance. The new route features a scalable CDI-mediated Lossen rearrangement as a substitution for hazardous azide chemistry that was employed in the original route.


2

Page 3 of 21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION Fabry disease is a rare X-linked genetic disorder that leads to the progressive accumulation of glycosphingolipids in lysosomes of a variety of cell types and tissues. Compound 1 is under investigation as an inhibitor of glucosylceramide synthase for potential use in Fabry and other neuropathic diseases.1, 2 In this paper, we report the development of a safe and scalable synthetic process that enabled kilogram-scale production of the required target compound.

RESULTS AND DISCUSSION The original small-scale synthesis of 1 by Discovery Chemistry involved four steps synthesis and

three

chromatographic

purifications

(Scheme

1):

formation

of

ethyl

2-(2-(4-

fluorophenyl)thiazol-4-yl)acetate 2 and a column purification; dimethylation using CH3I and sodium hydride in dimethylformamide, subsequent hydrolysis to acid 3 and a column purification; formation of the corresponding acyl azide 4 using sodium azide; Curtius rearrangement3 to isocyanate 5 and finally the formation of carbamate 1 upon treatment with (S)(+)-quinuclidinol and a column purification. This linear synthesis was fairly reliable for preparing 1 and related analogues because starting materials were commercially available, the Hantzsch thiazole ring formation normally gave good to excellent yields,4 and dimethylation and the carbamate formation through the isocyanate were both reliable reactions. While suitable for generating small supplies of 1, the early synthetic route posed challenges for scale up including a problematic dialkylation protocol, performing hazardous azide chemistry and highly-energetic


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 21

intermediates, and the need for chromatographic purifications in multiple steps. Thus, a chemical development effort commenced to address these process safety concerns and other scaling issues.

Scheme 1. First Synthesis of 1 Synthesis of Thiazole 2. The original batch-mode process to prepare thiazole 2 required heating ethyl 4-chloroacetoacetate and 4-fluorothiobenzamide in ethanol and was found to be exothermic with initiation at about 40 °C. The feasibility of performing this reaction in a dose-controlled mode was investigated in a calorimetry study. A solution of 4-fluorothiobenzamide in ethanol was adjusted to 55 °C. Ethyl 4-chloroacetoacetate was then dosed over a period of 30 min. The reaction was found to commence immediately with no inductive period and with little accumulation of reagent. The heat of reaction was -98 kJ/mol and the adiabatic temperature rise was 33 ˚C. This addition-controlled process was further developed and performed on kilogram scales. The thiobenzamide in ethanol was heated to gentle reflux, then ethyl 4-chloroacetoacetate


4

Page 5 of 21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


was added over a 2 h period to maintain the reaction at or below steady reflux. The reaction was kept at reflux for an additional 3 h to ensure its completion (HPLC analysis). During aqueous work up, the product was extracted into tert-butyl methyl ether (MTBE) and then solvent was swapped with heptane. Upon cooling at 0 ˚C, the thiazole ester 2 crystallized as a low-melting waxy solid in 65-80% yield with a purity of 98 A%, and was used directly in next step without further purification. Formation of intermediate 3 and control of impurities. In the discovery procedure, the dimethylation was achieved by adding excess iodomethane to a stirred mixture prepared from sodium hydride and ethyl 2-(2-(4-fluorophenyl)thiazol-4-yl)acetate in dimethylformamide (DMF). Initial attempts to replace the hazardous NaH/DMF5 reagent system involved evaluating iodomethane and 50% aqueous sodium hydroxide as dimethylation reagents in dimethyl sulfoxide (DMSO) as solvent. In this reaction, 4 equivalents of 50% aqueous sodium hydroxide were slowly added to a vigorously stirred solution of ethyl 2-(2-(4-fluorophenyl)thiazol-4yl)acetate and 4 equivalents of iodomethane in DMSO at 22 °C. Dimethylation was complete after 2 h. The product 6, along with about 10% of the methyl ester 6a that had formed was isolated in 96% combined yield and were saponified to the corresponding acid 3 in 85% yield (Scheme 2). Although this process showed feasibility, there were concerns regarding the use of aqueous sodium hydroxide in glass-lined equipment, and presence of residual amounts of DMSO in the isolated product and down stream products. After screening a variety of bases and solvents, an alternative process was developed which utilized potassium tert-butoxide and iodomethane in THF as an alternative reagent system. In order to achieve complete dimethylation, 4 equivalents each of the base and iodomethane were employed. The ethyl ester 2 was deprotonated by adding it as a solution in THF to a stirred


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 21

cloudy mixture of potassium tert-butoxide in THF. Iodomethane was then introduced slowly as a solution in THF at about 10 ˚C. The methylation reaction was essentially an instant reaction as iodomethane was introduced as monitored by HPLC. In addition, RC-1 calorimetry studies showed a pattern of sharp spikes in heat release after each increamental amount of iodomethane was added and subsequent fall almost to the baseline before more iodomethane was added. This saw-tooth profile of Qr vs. time was consistent with high reaction rate. Indeed, immediately after the addition was complete, >95% of the total conversion had already occurred. The reaction was deemed complete (>98% product) after stirring for 1 h at 10 oC. Remaining monomethylated impurity 8 was monitored at very low level (

Process Development of a GCS Inhibitor Including Demonstration of

Recommend Documents