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Exploring polymorphism: hydrochloride salts of pitolisant and analogues

Exploring polymorphism: hydrochloride salts of pitolisant and analogues
Exploring polymorphism: hydrochloride salts of pitolisant and analogues
Pitolisant hydrochloride is used to treat excessive daytime sleepiness in adults with narcolepsy. The drug is formulated as a crystalline solid, and a monoclinic P21 form has been claimed in patents, but little additional information about the structure and polymorphism of the compound has been published. No new forms were obtained when we grew crystals from solution under various conditions. Reexamination of the crystals revealed a disordered and partially hydrated structure that resembles the one reported earlier but is not identical. Further insight was obtained by synthesizing analogues of pitolisant with its Cl substituent replaced by Me, F, and Br, followed by structural analysis of the hydrochloride salts by X-ray diffraction. Pitolisant hydrochloride and its three analogues showed very similar solid-state behavior, and each compound yielded new metastable forms when crystallized from melts. The lifetime of metastable Form III of pitolisant hydrochloride could be extended significantly by adding small amounts of the fluoro analogue, but none of the metastable forms could be obtained as single crystals suitable for structural analysis. Computational predictions of the polymorphic landscapes of pitolisant hydrochloride and its analogues identified possible structures of the metastable forms. Dual experimental and computational approaches are already widely used in polymorphic screening, but our work shows the value of broadening these searches to include sets of structural analogues.
crystal structure prediction, polymorphism
1528-7483
1268-1283
Patel, Jessica
e61d0fb5-c233-4dfb-935e-ae0819781b5c
Leduc, Zachary
820f827d-bc98-482c-ba5b-35117b319b7a
Avila, Aaron Gabriel Nunez
8b031a01-2f7c-4160-a6b3-614fbe1fd8ab
Glover, Joseph
27469618-4dd0-44c1-8267-ff955bce66b7
Wu, Kelin
c7021cf2-abd3-4c1f-99f8-25b1be2c4df6
Zhang, Yuxing
d4b4659f-3b29-4a9a-b77f-6c94a9a0e43f
Zhang, Jing
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Zhai, Xiaoting
5049cedf-af24-4ad4-b14c-d92cbd6fc5b6
Jing, Huize
69b626eb-3c8e-48be-9747-a84fee3b5ac9
Chen, Alex M.
aca45724-dd5c-4102-9f22-3c249e589918
Chartrand, Daniel
a9278217-d2a0-483f-8359-d497118a07f7
Maris, Thierry
58297798-213a-4041-bf9d-3982eeb39778
Day, Graeme M.
e3be79ba-ad12-4461-b735-74d5c4355636
Wuest, James D.
6ebbbf8a-d744-4dcf-88ec-db273226ab77
Patel, Jessica
e61d0fb5-c233-4dfb-935e-ae0819781b5c
Leduc, Zachary
820f827d-bc98-482c-ba5b-35117b319b7a
Avila, Aaron Gabriel Nunez
8b031a01-2f7c-4160-a6b3-614fbe1fd8ab
Glover, Joseph
27469618-4dd0-44c1-8267-ff955bce66b7
Wu, Kelin
c7021cf2-abd3-4c1f-99f8-25b1be2c4df6
Zhang, Yuxing
d4b4659f-3b29-4a9a-b77f-6c94a9a0e43f
Zhang, Jing
715e718b-73ec-4137-b7d0-56c3067f1924
Zhai, Xiaoting
5049cedf-af24-4ad4-b14c-d92cbd6fc5b6
Jing, Huize
69b626eb-3c8e-48be-9747-a84fee3b5ac9
Chen, Alex M.
aca45724-dd5c-4102-9f22-3c249e589918
Chartrand, Daniel
a9278217-d2a0-483f-8359-d497118a07f7
Maris, Thierry
58297798-213a-4041-bf9d-3982eeb39778
Day, Graeme M.
e3be79ba-ad12-4461-b735-74d5c4355636
Wuest, James D.
6ebbbf8a-d744-4dcf-88ec-db273226ab77

Patel, Jessica, Leduc, Zachary, Avila, Aaron Gabriel Nunez, Glover, Joseph, Wu, Kelin, Zhang, Yuxing, Zhang, Jing, Zhai, Xiaoting, Jing, Huize, Chen, Alex M., Chartrand, Daniel, Maris, Thierry, Day, Graeme M. and Wuest, James D. (2024) Exploring polymorphism: hydrochloride salts of pitolisant and analogues. Crystal Growth & Design, 24 (3), 1268-1283. (doi:10.1021/acs.cgd.3c01245).

Record type: Article

Abstract

Pitolisant hydrochloride is used to treat excessive daytime sleepiness in adults with narcolepsy. The drug is formulated as a crystalline solid, and a monoclinic P21 form has been claimed in patents, but little additional information about the structure and polymorphism of the compound has been published. No new forms were obtained when we grew crystals from solution under various conditions. Reexamination of the crystals revealed a disordered and partially hydrated structure that resembles the one reported earlier but is not identical. Further insight was obtained by synthesizing analogues of pitolisant with its Cl substituent replaced by Me, F, and Br, followed by structural analysis of the hydrochloride salts by X-ray diffraction. Pitolisant hydrochloride and its three analogues showed very similar solid-state behavior, and each compound yielded new metastable forms when crystallized from melts. The lifetime of metastable Form III of pitolisant hydrochloride could be extended significantly by adding small amounts of the fluoro analogue, but none of the metastable forms could be obtained as single crystals suitable for structural analysis. Computational predictions of the polymorphic landscapes of pitolisant hydrochloride and its analogues identified possible structures of the metastable forms. Dual experimental and computational approaches are already widely used in polymorphic screening, but our work shows the value of broadening these searches to include sets of structural analogues.

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Patel_CGD_Pitolisant_Manuscript_Revised_2 - Accepted Manuscript
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More information

Accepted/In Press date: 3 January 2024
e-pub ahead of print date: 23 January 2024
Published date: 23 January 2024
Additional Information: Publisher Copyright: © 2024 American Chemical Society
Keywords: crystal structure prediction, polymorphism

Identifiers

Local EPrints ID: 485976
URI: http://eprints.soton.ac.uk/id/eprint/485976
ISSN: 1528-7483
PURE UUID: a11a81d3-cfc8-4922-b999-899430c638b1
ORCID for Joseph Glover: ORCID iD orcid.org/0000-0002-5281-6664
ORCID for Graeme M. Day: ORCID iD orcid.org/0000-0001-8396-2771

Catalogue record

Date deposited: 04 Jan 2024 18:25
Last modified: 30 Aug 2024 02:01

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Contributors

Author: Jessica Patel
Author: Zachary Leduc
Author: Aaron Gabriel Nunez Avila
Author: Joseph Glover ORCID iD
Author: Kelin Wu
Author: Yuxing Zhang
Author: Jing Zhang
Author: Xiaoting Zhai
Author: Huize Jing
Author: Alex M. Chen
Author: Daniel Chartrand
Author: Thierry Maris
Author: Graeme M. Day ORCID iD
Author: James D. Wuest

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