Synthesis of Stilbene and Chalcone Inhibitors of Influenza A Virus by SBA-15 Supported Hoveyda-Grubbs Metathesis

Round 1

Reviewer 1 Report

See attached file

Comments for author File: Comments.pdf

Author Response

Referee 1

Q1: The first one regards with the catalyst characterization, which in my point of view is rather limited. It will be at least very useful to provide the porosity of the material before and after grafting the ruthenium complex. So that, this could help to determine if the complexes are inside the pores or just on the surface and if the reaction takes place inside the material or simply on its surfaces.

A1: The textural parameters for SBA-15 before and after the grafting of ASIPr have been evaluated. A novel Table (Table 1) reporting BET surface area, void volume and average pore diameter has been inserted in the text, while the relative isotherms are in SI#1. The following sentence has been also introduced in the text to comment the data: “Nitrogen adsorption isotherms showed that SBA-15 retained the mesoporous structure and pore size distribution after the loading of ASIPr , in accordance with data previously reported [43]. BET surface area, void volume and average pore diameters of SBA-15 and ASIPr/SBA-15 are showed in Table 1; the relative isotherms are in SI#1. The slight decrease of the mesopore volume (from 1.12 to 0.98 cm³/g) and BET surface area (from 861 to 693 m²/g) confirmed the loading of the catalyst. Moreover, the variation in the average value of the pore diameter in ASIPr/SBA-15 with respect to native SBA-15 (from 5.5 to 5.4) suggested the presence of the complex inside the pore”. [Page: 3 Line: 108] In particular, textural data suggest that ASIPr is mainly loaded inside the pores of the Line:

Q2: My second concern regards with the amount of leached catalyst. It is not clear to me how this

leaching is computed. This may be detailed in the experimental section but I have the impression that this must be explicitly described in the main text and relate this amount of leached catalyst the amount of ruthenium in the final products. As mentioned this is a key point for biologically relevant species.

A2: The procedure for the evaluation of the leaching of ASIPr is now detailed in the text by the following sentence “The leaching of ruthenium in the recyclability experiments after any runs was evaluated by ICP-MS analysis of the reaction mixture after removal of the heterogeneous catalyst by filtration”. Moreover, the following sentence has been also added to comment the data: “The partial leaching of ASIPr during different runs may be responsible for the slight decrease in the conversion and yield of reactions, this leaching behavior being in accordance with data previously reported for similar catalyst”. [Page: 6 Line: 230].  Note that reaction products are further purified by flash-chromatography (as reported in the experimental part) before the biological test.

Q3: Finally, the total conversion and the final yield differ significantly. I wonder if this implies the

formation of side products. If this is the case authors should specify their nature. In particular,

how important are the homocoupling processes in the cross-metathesis reaction involving

two different substrates.

A3: A comment about the nature of the side products is now reported in the following sentence: “The low mass-balance of the self, cross and ring-closing metathesis reactions suggested the occurrence of oligomerization processes to yield high molecular weight products not isolable from the reaction mixture”. [Page: 5 Line: 199].  In the case of the cross metathesis some homo-coupled products were also obtained as reported in Table 2”.  As requested by the referee, the yield of homo-coupling products versus cross-coupling counterpart is now detailed in Table 2. As a general trend, the cross-coupling process prevailed on the homo-coupling side reaction under reported experimental conditions.

Q4: I would suggest to increase the number of reference to at least other Grubbs catalyst supported on silica materials. There is a large amount of examples, some of them with

a better characterization of the material than some of the reported ones.

A4: More references about Grubbs catalyst supported on SBA-15 have been added in the introduction paragraph.

Q5: I would include a general scheme in the introduction showing the main aim of the

work.

A5: In accordance with the referee suggestions a new general scheme has been introduced in the text

Reviewer 2 Report

The authors described application of Hoveyda-Grubbs catalyst immobilized on SBA-15 for metathesis applications. I recommend it for publication when considering my comments.

Literature – Balcar Coord Chem Rev 2013 discusses immobilization of metathesis catalysts in general needs to be discussed and compared. While the catalytic part is nicely prepared, there is no information about the support. What does it mean … ASIPr/SBA-15 was prepared by applying a slightly modified procedure reported in literature ? This is absolutely not sufficient. SBA-15 material is not characterized at all. Textural parameters are not provided. Catalyst prepared are characterized only by ICP-MS. How looks XRD pattern ? How looks adsorption isotherms before and after immobilization or even after catalytic runs.

Author Response

Referee 2

Q1: Literature – Balcar Coord Chem Rev 2013 discusses immobilization of metathesis catalysts in general needs to be discussed and compared.

A1: The reference suggested by the referee has been added in the introduction paragraph and discussed by the following sentence: “The preparation, structural characterization and application of mesoporous molecular sieves as advanced support for olephin metathesis catalyst is reviewed”. [Page: 1 Line: 66].

Q2: While the catalytic part is nicely prepared, there is no information about the support. What does it mean… ASIPr/SBA-15 was prepared by applying a slightly modified procedure reported in literature ? This is absolutely not sufficient. SBA-15 material is not characterized at all. Textural parameters are not provided. Catalyst prepared are characterized only by ICP-MS. How looks XRD pattern ? How looks adsorption isotherms before and after immobilization or even after catalytic runs.

A2: We agree with the referee suggestions, more structural data about ASIPr/SBA-15 and SBA-15 are now added in the revised version. In particular, the textural parameters for SBA-15 before and after the grafting of ASIPr have been evaluated. A novel Table (Table 1) reporting BET surface area, void volume and average pore diameter has been inserted in the text, while the relative isotherms are in SI#1. The following sentence has been also introduced in the text to comment the data: “Nitrogen adsorption isotherms showed that SBA-15 retained the mesoporous structure and pore size distribution after the loading of ASIPr , in accordance with data previously reported [43]. BET surface area, void volume and average pore diameters of SBA-15 and ASIPr/SBA-15 are showed in Table 1; the relative isotherms are in SI#1. The slight decrease of the mesopore volume (from 1.12 to 0.98 cm3/g) and BET surface area (from 861 to 693 m2/g) confirmed the loading of the catalyst. Moreover, the variation in the average value of the pore diameter in ASIPr/SBA-15 with respect to native SBA-15 (from 5.5 to 5.4) suggested the presence of the complex inside the pore”. [Page: 3 Line: 108] Since this data are full in accordance with results previously reported ref[43], XRD pattern is beyond the scope of the manuscript.

Reviewer 3 Report

The manuscript submitted reports (1) preparation of series of stilbene and chalcone derivatives using self-, cross- and ring-closing metathesis over Hoveyda-Grubbs type metathesis catalyst immobilized on SBA-15 molecular sieves and (2) testing of these compounds as concerns their antiviral activity against influenza A virus. Manuscript is worth to be published in Catalysts after following issues being addressed:

1.The recent review about metathesis catalyst on SBA-15 (Catalysts 2019, 9(9), 743) should be cited in Introduction. Similarly the article about preparation of hydroxystilbenoids ( J. Org. Chem. 2005, 3319–3325).

2.The origin of SBA-15 and especially its characteristics (pore size) should be given.

3.The amounts of catalyst used in metathesis experiments is missing. Please, add either Ru concentration in reaction medium or molar ratio substrate/Ru; it is important not only from catalytic point of view, but it enables to asses the product contamination by Ru.

4.Minor defects: (a) In definition of IC₅₀ (line 218) there should be probably µg/ml instead of mg/ml; (b) After complete disappearing of substrate….. (line 325) – 100% substrate conversion has not been achieved according Table 1, however; (c) The last part of the text I would call Conclusions instead of Discussion.

Author Response

Referee 3

Q1: The recent review about metathesis catalyst on SBA-15 (Catalysts 2019, 9(9), 743) should be cited in Introduction. Similarly the article about preparation of hydroxystilbenoids ( J. Org. Chem. 2005, 3319–3325).

A1: The novel references have been added in the introduction paragraph

Q2: The origin of SBA-15 and especially its characteristics (pore size) should be given.

A2: The section “ general procedure” including the origin of SBA-15 has been introduced in Materials and methods paragraph, moreover the  textural parameters for SBA-15 before and after the grafting of ASIPr are now reported in Table 1 and discussed in the text.

Q3: The amounts of catalyst used in metathesis experiments is missing. Please, add either Ru concentration in reaction medium or molar ratio substrate/Ru; it is important not only from catalytic point of view, but it enables to assess the product contamination by Ru. Note that reaction products are further purified by flash-chromatography (as reported in the experimental part) before the biological test.

A3: Data, on the molar ratio substrate/Ru are reported in the revised version. [Page: 3 Line: 131]

Q4. In definition of IC50 (line 218) there should be probably µg/ml instead of mg/ml;

A: Ok done.

Q5. After complete disappearing of substrate…. (line 325) – 100% substrate conversion has not been achieved according Table 1

A: The sentence has been modified accordingly. [Page: 10 Line: 360]

Q6 The last part of the text I would call Conclusions instead of Discussion.

A6: Ok Done

Round 2

Reviewer 2 Report

This is the second review - I have just a few marginal comments.

Author Response

Q1:Line 111 - the relative isotherms are in SI#1. - I supposed it should be related isotherms and not relative.

A: Text has been modified accordingly.

Q2:Table 2 - cData in parentheses are referred to self-metathesis by-products. - this should be specified in more detail.

A: A new sentence " ^cData in parentheses are referred to self-metathesis by-products obtained during the cross-metathesis reactions. Compound 9 is the side-product deriving from the homocoupling of 2; compound 10 is the side-product deriving from the homocoupling of 3; compound 12 is the side-product deriving from the homocoupling of 5." is now added at line 167.