PONE-D-20-29935

Synthesis and analysis of 4-(3-fluoropropyl)-glutamic acid stereoisomers to determine the stereochemical purity of (4S)-4-(3-[18F]fluoropropyl)-L-glutamic acid ([18F]FSPG) for clinical use

PLOS ONE

Dear Dr. Hsin,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

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We look forward to receiving your revised manuscript.

Kind regards,

Yu-Hsuan Tsai

Academic Editor

PLOS ONE

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Additional Editor Comments (if provided):

Please address all points of the reviewers.

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Reviewers' comments:

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Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: 1: The half life of 18F is 109.7 min, it is more approprite to round its half life to 110 min, rather than109 min.

2: The separation resolution of four stereoisomers showed in Fig 7 is much better than in Fig 6.

Their corresponding HPLC separation conditions, ranging from column length, solvent (IPA vs MeCN), temperature (23 centigrade vs 22 centigrade) to running time (15 min vs 25 min) are differnt. Compared with Fig 6, which one (or several) is the key point for good resolution? In Fig 6, column temperature proves to be crucial, but in Fig 7, it is hard to draw any conclusions for the improved resolution performance. Studies in Fig 7 will be more helpful only if it could offer some useful advices for people who may use your HPLC condition for similar seperation, otherwise, it is confusing

3: More comparision studies need to be done to figure out what really matters for a good resolution. Temperature? Column length? Solvent or running time? The lack of such experiments devalues this paper.

Reviewer #2: The manuscript by Ling-Wei Hsin et al. submitted to Plos one described Synthesis and analysis of 4-(3-fluoropropyl)-glutamic acid stereoisomers to determine the stereochemical purity of (4S)-4-(3-[18F]fluoropropyl)-L-glutamic acid ([18F]FSPG). This study described in detail the synthesis of the four isomers of 4-(3-Fluoropropyl)-glutamic acid and their HPLC liquid phase conditions, as well as the radiolabeling of [18F]FSPG, which is of great value for clinically promoting the transformation of [18F]FSPG . But there are also the following issues that need to be further supplemented.

1: The F-19 NMR spectra and optical rotations of compounds (2S, 4S)1, (2S, 4R)1, (2R, 4R)1 and (2R, 4R)1 should be added in this manuscript.

2：Why (S) 8 can be converted to (2S,4R) 11, but the related literature of FSPG can only get (2S,4S) derivatives, this reason should be explained in this manuscript.

3: Since the purpose of this article is to promote the clinical production of [18F]FSPG, the detailed steps of radiolabeling in the article should be described, and the average yield of multiple high-dose labeling should be provided.

4：The physical and chemical properties of the final product [18F]FSPG should be provided.

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PONE-D-20-29935R1

Synthesis and analysis of 4-(3-fluoropropyl)-glutamic acid stereoisomers to determine the stereochemical purity of (4S)-4-(3-[18F]fluoropropyl)-L-glutamic acid ([18F]FSPG) for clinical use

PLOS ONE

Dear Dr. Hsin,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by Dec 24 2020 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

• A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.
• A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.
• An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

We look forward to receiving your revised manuscript.

Kind regards,

Yu-Hsuan Tsai

Academic Editor

PLOS ONE

Additional Editor Comments (if provided):

Thanks for submitting the revised manuscript, which has addressed the comments raised by the reviewers. However, there are three points I would like the authors to address.

1. Please add a statement about the use of CuSO4 at 2 mM. Why specifically at this concentration?

2. Most peaks in Figs S13, S15, S17 are difficult to observe, please provide an enlarge image to show those peaks with clear splitting patterns.

3. 13C of (2S,4R)-11 contains too much impurities. Please update the spectrum using pure material.

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

Synthesis and analysis of 4-(3-fluoropropyl)-glutamic acid stereoisomers to determine the stereochemical purity of (4S)-4-(3-[18F]fluoropropyl)-L-glutamic acid ([18F]FSPG) for clinical use

PONE-D-20-29935R2

Dear Dr. Hsin,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Kind regards,

Yu-Hsuan Tsai

Academic Editor

PLOS ONE