Obtainment of Threo and Erythro Isomers of the 6-Fluoro-3-(2,3,6,7,8,9-hexahydronaphtho[2,3-b][1,4]dioxin-2-yl)-2,3-dihydrobenzo[b][1,4]dioxine-5-carboxamide

Round 1

Reviewer 1 Report

The manuscript contains interesting results in the field of organic synthesis. For its publication, it is necessary to remove the discrepancy - in the discussion it is stated that the main products of the synthesis are stereoisomers 1a and the side products are stereoisomers 1b, but in the description of the experiments in the experimental part only the isolation of stereoisomers 1b is mentioned. Also the conversions of stereoisomers 1a to the corresponding stereoisomers 1b, which are mentioned in the discussion, are missing in the experimental part.

 Other comments:

The values of substance amounts should be rounded to match the accuracy of the mass values (volume value in the case of bromine): line 192, 10.1 mmol; line 175, 20.1 mmol; line 194, 10 mmol; line 211, 5.8 mmol; line 218, 2.9 mmol; line 236, 2.1 mmol; line 237, 2.0 and 2.2 mmol; line 253, 1.3 mmol.

Line 219: "a 0°C" should be corrected to "at 0 °C".

Line 242: "2 erythro" should be corrected to "1b erythro" and if the product weight is correctly 0.19 g, the yield is 24%.

Lines 243 and 255: Calculated mass is 408.1218 (smaller by the difference in the masses of Na and Na⁺), m/z value 140.1289 and 140.1277 respectively, should be interpreted.

Line 254: The temperature at which decomposition starts should be given.

Reference [1] appears to be incomplete (web address and download date, eventually date of publication are not given).

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The authors Valentina Straniero and co-workers submitted the manuscript entitled „6-Fluoro-3-(2,3,6,7,8,9-hexahydronaphtho[2,3-b][1,4]dioxin-2-yl)-2,3-dihydrobenzo[b][1,4]dioxine-5-carboxamide (threo and erythro isomers)” to the MDPI journal “molbank” in order to be considered for publication as a short note.

The manuscript reports on the chemical synthesis and analytical characterization of Erythro 6-Fluoro-3-(2,3,6,7,8,9-hexahydronaphtho[2,3-b][1,4]dioxin-2-yl)-2,3-dihydrobenzo[b][1,4]dioxine-5-carboxamide respectively the Threo isomer, both occurring as side products in the synthesis of carboxamide-based compounds designed as antibacterial compounds targeting FtsZ. The manuscript is clearly structured and well written. However, I would like to make some suggestions that could help to further improve the manuscript:

“…worrying problem of antimicrobial resistance” Personally, I would briefly give some examples here of what resistance development is due to, such as efflux pumps (e.g., https://doi.org/10.1186/s12866-021-02250-x), porin protein loss causing reduced antibiotic uptake (e.g., https://doi.org/10.1128/spectrum.00148-22) among others (e.g., https://doi.org/10.1016/j.micpath.2021.104915). This highlights the complexity of the underlying mechanisms and underscores the importance of developing new antibacterial drugs, as the authors of the study have followed.

“In the last years, a huge number of FtsZ inhibitors have been developed” It is suggested to consider recent reviews also from other research groups, e.g.: https://doi.org/10.1016/j.bioorg.2019.103169 and https://doi.org/10.1111/febs.15489

Perhaps it is possible to include the chemical structure of PC190723 in Figure 1 to allow comparison?

“having a fluorescent analogue (Figure 2) for investigating the mechanism of action” Can the authors briefly outline what the studies should look like, that it absolutely requires coupling to a fluorescent indicator. Distribution in the cells? The authors should briefly mention in the manuscript why the fluorine atoms present are not used for this, in the context of PET (https://doi.org/10.1002/anie.202204955) NMR (https://meetings.aps.org/Meeting/MAR23/Session/N00.327), or MAS (https://doi.org/10.1039/C9DT03330K) studies. By adding a fluorescent dye, a new chemical entity is created. If the analysis were based on fluorine, this would not be the case.

Scheme 1: It is somewhat surprising that the tetrahydronaphthalenediol is not assigned compound number 1 (no number at all), but the final product is formed from intermediate 7 and is then titled with number 1.

“the first two hydrogens were the ones of the 1,4-dioxane and the second ones the two of the epoxide” Please provide the chemical shift in ppm.

“The purity was quantified at their λ max” Please provide the particular wavelengths.

Did the authors also perform IR spectroscopy to complete the data set for analytical characterization? The disappearance of the vibration of the alcohol could allow a distinction between 1a and 1b in each case (besides the loss of one fluorine substituent). The IR data of the final products could be provided by the authors as a supplement. And what about the CHN analysis? Did the authors waive it in favor of HRMS?

Although there will be a close editing by the MDPI publisher, the authors are kindly asked to correct formal errors and inconsistency, such as: Case shift (also SI), bold (e.g., Scheme 1), space with units, presentation of the references, writing out of numbers (e.g., line 126, 134), consistent use of abbreviations (e.g., min, h), typos, subscript (SI), use of dash (SI).

A short information about the antibacterial activity of the end products (and also of the by-products) would be interesting, but this is probably beyond the scope of the short note and will certainly be taken up in a comprehensive follow up paper. Then, FtsZ as a target of these compounds should also be verified experimentally.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Lines 2, 17, 80, 183, 192, 200, 210, 219, 226, 243, 244, 270, 272, 304, 306, and 400: "[2,3-b]" should be corrected to "[2,3-b]" ("b" in italics).

Line 228: Still need to correct "a 0°C" to "at 0°C".

Lines 243 and 270: One left parenthesis is missing from the compound names. The correct name is 2,6-difluoro-3-(2-(2,3,6,7,8,9-hexahydronaphtho[2,3-b][1,4]dioxin-2-yl)-2-hydroxyethoxy )benzamide.

Line 274: "1a and 1b erythro" should be "1a erythro and 1b erythro".

Line 280: The character δ should be added before the first chemical shift value.

The heading on lines 293 and 294 should be changed to "Conversion of 1a erythro to 1b erythro". A separate paragraph should then be devoted to the conversion of 1a threo to 1b threo (similarly to the preparation of 1a threo and 1b threo starting from 7 threo.

The abbreviation et al. should not be used in references; in references [5,15,19-21], it would be appropriate to add the authors instead.

Author Response

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