Modular assembly of chiral amino acid derivatives and peptides from commonly available feedstocks

Domain: chemistry
Published: 2025-12-30
Editorial outcome: minor_revision

Abstract
α-Amino acids are fundamental components of proteins and natural molecules, with non-natural variants highly valued in both academia and industry for their ability to tune chemical, physical, and pharmaceutical properties. Herein, we report a photoredox-catalyzed protocol for the synthesis of optically active α-amino amides from readily available aldehydes, amines, and formamides. A dual catalytic system combining a chiral sodium phosphate with tetrabutylammonium decatungstate (TBADT) under visible light enables this transformation. The process achieves high enantioselectivity and allows two-step conversion to free amino acids without significant racemization. Consequently, diverse, synthetically useful structures—including β-branched and α,β-diamino acid derivatives, glycosylated amino acids, isotopically labeled compounds (deuterium and 15N), and peptides—have been rapidly constructed. Flow chemistry further broadens substrate tolerance and eliminates prefunctionalization steps. Here, we show that leveraging TBADT-driven carbamoyl radical generation and chiral catalysis provides a practical route to diverse chiral scaffolds, thereby advancing peptide synthesis and drug discovery.

Introduction
Amino acids serve as fundamental building blocks in nature, constituting core structural motifs of proteins and numerous other biologically important molecules (Fig. 1a)1–5. Beyond their natural functions, amino acids and their derivatives—particularly non-proteinogenic variants—have gained increasing importance in pharmaceutical development, material science, and asymmetric catalysis6. The recent surge in peptide-based therapeutics, accelerated by advances in screening technologies like mRNA display, has intensified the demand for structurally diverse amino acids with precise stereochemical control7. This technology enables the incorporation of non-natural amino acids into vast peptide libraries, significantly expanding the structural and functional diversity of potential drug candidates8. Consequently, developing efficient, scalable, and economical methods for synthesizing enantiomerically pure amino acids from readily available precursors has become increasingly urgent for advancing peptide drug discovery and development9. Traditional approaches to synthesizing chiral α-amino acids rely predominantly on polar/heterolytic processes10. These include asymmetric hydrogenations of dehydroamino acids11 or α-imino esters12,13, electrophilic aminations of enolates14, alkylations of glycine derivatives via phase-transfer catalysis15 and through Pd/Cu synergistic catalytic systems16,17, and nucleophilic additions to α-imino esters18. More recent advances include asymmetric Ugi-type multicomponent reactions, which are highly valuable but involve odorous and toxic isocyanides19. Other developments involve stereocontrolled 1,3-nitrogen migration via metal-catalyzed nitrene insertion that relies on activated nitrogen sources20,21.

In recent years, radical-based methods22,23 have emerged as promising alternatives for asymmetric amino acid synthesis. Notably, nickel-catalyzed enantioconvergent cross-coupling of racemic α-haloglycine derivatives with alkylzinc reagents (Fig. 1b), and cobalt-catalyzed asymmetric reductive alkylation of dehydroglycine derivatives with alkyl halides (Fig. 1c) have demonstrated the potential of radical chemistry to overcome limitations of traditional approaches24–26, albeit that pre-prepared substrates with specific activation groups are still required. Among various radical species, carbamoyl radicals are particularly attractive for amino acid synthesis due to their nucleophilic character and potential for direct amide bond formation27. However, prevalent strategies for harnessing carbamoyl radicals typically rely on 4-substituted-1,4-dihydropyridines (DHPs) as precursors28–30, requiring multi-step synthesis and offering limited substrate scope, albeit that the generation of carbamoyl radicals from formamides via hydrogen atom transfer (HAT) is known for racemic Minisci-type carbamoylations31,32 and hydrocarbamoylations33. The most recent approach employs visible light and Lewis acid activation of DHPs to generate carbamoyl radicals for three-component reactions with in situ-formed imines or iminiums34, yet asymmetric variants remain undeveloped (Fig. 1d). Alternative strategies using simple formamides as carbamoyl anion precursors require strong bases (e.g., LDA) and chiral auxiliaries35, limiting practical applications (Fig. 1e). Thus, a general, catalytic asymmetric strategy to harness carbamoyl radicals from simple formamides for the synthesis of amino acid derivatives remains an unmet challenge.

Herein, we report a dual catalytic system that integrates a HAT-mediated carbamoyl radical generation with a stereocontrolled ionic and H-bonding activated asymmetric addition between carbamoyl radical and an in situ formed imine. This strategy enables rapid and modular assembly of α-amino amides from readily available aldehydes, amines, and formamides (Fig. 1f). We sort out the cumulative challenges that compatibility among the individual species in the reaction mixture (catalysts, substrates, intermediates), side reactions, catalyst deactivation, realization of broad substrate scope. The developed protocol affords a wide range of α-amino amide derivatives (>80 examples) with up to >99% yield and >99% enantioselectivity.

Results
Reaction optimization
We initiated our investigation with a reaction of N-tert-butylformamide (1a), cyclohexanecarbaldehyde (2a), and 3,4,5-trimethoxyaniline (3a, TMP-NH₂) to synthesize chiral α-amino amide 4a. Tetrabutylammonium decatungstate (TBADT), a well-established hydrogen atom transfer (HAT) catalyst36,37, was selected to generate a carbamoyl radical from formamide 1a under irradiation with a 10W 390 nm LED at room temperature. This nucleophilic radical was anticipated to undergo addition to the in situ formed imine, affording product 4a. Initial experiments conducted without a Brønsted acid co-catalyst38,39 yielded the desired product in 81% yield, albeit in racemic form (Table 1, entry 1). Although the introduction of chiral phosphoric acid 5a only induced 6% ee (entry 2), employing the more sterically demanding TRIP catalyst (5b) significantly improved enantioselectivity to 37% ee, suggesting that the chiral Brønsted acids could control the stereochemical outcome by activating the imine substrate (entry 3). The enhanced enantioselectivity likely results from more effective facial discrimination of the imine intermediate due to the increased steric bulk around the active site.

We then explored the effect of various counterions by evaluating the corresponding phosphate salts (entries 4–7). The sodium salt catalyst exhibited the most promising results in terms of both yield and enantioselectivity. We hypothesize that the sodium cation provides an optimal balance of Lewis acidity for imine activation while maintaining appropriate solubility and catalyst conformation40,41. Modification of the 3,3’-position on the BINOL backbone from TRIP to 2,4,6-tricyclopentylphenyl substituents (Na[5c]) afforded quantitative yield with slightly enhanced enantioselectivity (entry 8 vs. entry 4), supporting our strategy of tuning the chiral pocket’s steric environment. Further optimization of reaction parameters revealed that the solvent composition and ratio (MeCN:DCM) substantially influenced both yield and enantioselectivity (entries 9–10). This solvent effect likely stems from changes in the imine formation equilibrium and the organization of the transition state assembly. Lowering the reaction temperature to −30°C considerably improved enantioselectivity to 68% (entry 11). Increasing the light source power to 40W further enhanced the ee to 74% (entry 12). When the reaction was conducted at −78°C, the enantioselectivity increased dramatically to 93% ee, albeit with diminished yield (58%, entry 13). Extending the reaction time to 48 h at −78°C proved optimal, furnishing product 4a in 85% yield with excellent enantioselectivity (96% ee, entry 14). Chiral Brønsted acid 5c instead of its sodium salt provided the product with diminished yield and similar enantioselectivity (67%, 95% ee; entry 15 vs. entry 14). Notably, reducing the sodium chiral phosphate catalyst loading to 10 mol% (entry 16) resulted in only slightly diminished yield and enantioselectivity, indicating that lower catalyst loadings remain viable for practical applications.

Substrate scope
Having established optimal reaction conditions, we proceeded to explore the substrate scope of this transformation. We began by investigating various formamide derivatives while maintaining cyclohexanecarbaldehyde (2a) and 3,4,5-trimethoxyaniline (3a) as standard coupling partners (Fig. 2). The optimized conditions proved effective across a diverse range of formamides. Primary formamide was also tolerated, affording product 4b in 95% yield, albeit with lower enantioselectivity (73% ee) compared to 4a, suggesting that increased steric bulk on the formamide might be beneficial for enantiocontrol. Under this guidance, we found N-methyl (4c), N-ethyl (4d), N-isopropyl (4e) and other formamides (4f, 4g) were well-tolerated, delivering the desired products in moderate to excellent yields (53-91%) and higher enantioselectivities (83-93% ee). Notably, the reaction accommodated formamides bearing cyclic motifs of varying ring sizes. The cyclopropyl derivative 4h (96% yield, 65% ee) and cyclohexyl derivative 4i (98% yield, 93% ee) were obtained in excellent yields, though with some variation in enantioselectivity. Sterically demanding formamides (4j, 4k) afforded the corresponding products in lower yields but maintained good stereoselectivity. N-Aryl formamide could also undergo the reaction, albeit with lower yield and enantioselectivity (4l). We next examined the scope with respect to the aniline component. Aniline (4m) and para-substituted anilines bearing various functional groups including F (4n), Cl (4o), Br (4p), Me (4q), OMe (4r), and OPMP (4s) were all compatible with the reaction conditions, furnishing products in generally high yields (68-98%) and excellent enantioselectivities (82-95% ee). Meta-substituted anilines (4t-4y) displayed similar reactivity, with yields ranging from 63% to 78% and consistently high enantioselectivities (88–94% ee). Ortho-substituted anilines were not tolerated, probably due to steric effect. The formamides derived from secondary amines (e.g., DMF) could not undergo the reaction (Please see Supplementary Information for details, Page S54). The methodology also accommodated more elaborate substitution patterns, as exemplified by products 4z-4ad (67–93% yield, 80–94% ee).

Having established the broad compatibility of formamides and anilines, we next explored the scope with respect to the aldehyde components (Fig. 3). Cyclic aliphatic aldehydes performed exceptionally well, with cyclopentyl (6a) and 4,4-difluoro-cyclohexyl (6b) derivatives providing high yields (88-99%) and excellent enantioselectivities (93–95% ee). Aldehydes derived from tetrahydropyran (6c) and N-Boc piperidine (6d) maintained high stereoselectivity (94–98% ee). Other aliphatic aldehydes (6e-6l), including simple unbranched and variously branched structures, consistently delivered the desired products with high enantioselectivities (78–92% ee). Notably, the protocol accommodated diverse functional groups including alkenes (6m), alkynes (6n), halogens (6o, 6p), and protected functionalities (6q, 6r), providing orthogonal functionalities for subsequent molecular assembly, all delivering products with good stereoselectivity (86–94% ee). Aliphatic aldehydes with aromatic substituents, 6s-6u, also delivered high enantioselectivities (85–90% ee). Aromatic aldehydes could also undergo the reaction, albeit with much lower yield and enantioselectivity, e.g., benzaldehyde (Ar-TM, 46%, 37% ee). α-Substituted racemic aldehydes (6v-6x) afforded β-branched non-canonical amino acid derivatives, valuable molecules in modern drug development efforts42, with up to 8:1 diastereoselectivities and moderate to high enantioselectivities (71–85% ee). These products exhibited syn-selectivity, which aligns well with the Felkin-Anh model43 for α-substituted imines44,45, as shown in TS-1. The methodology could also be applied to more complex substrates. For example, oleic aldehyde (6y), aldehyde derived from erucic acid (6z), citronellal (6aa), and cyclamen aldehyde (6ab) were successfully transformed with good stereoselectivity (78–92% ee/de). The methodology’s compatibility with bioactive molecule-derived components was demonstrated through the successful incorporation of orlistat (6ac) and dopamine (6ad) moieties, underlining potential applications in medicinal chemistry and late-stage functionalization.

To demonstrate the broader utility of our methodology, we extended its application to more structurally complex and biologically important targets, including α,β-diamino amides46,47, glycosylated amino acids48, and peptides (Fig. 4). First, the reaction was applied to chiral N-Boc α-amino aldehydes for synthesizing α,β-diamino amides. Under standard conditions, the aldehyde derived from L-phenylalanine afforded the corresponding syn-α,β-diamino amide syn-7a with excellent diastereoselectivity, 38% yield and 98% ee. Interestingly, conducting the reaction at −30°C without the chiral sodium phosphate catalyst still provided syn-7a with 34% yield and 93% ee. This high intrinsic diastereoselectivity likely originates from substrate control49, and the anti-Felkin-Anh selectivity could be attributed to TS-2, featuring an intramolecular hydrogen bond between the Boc-N-H and the imine. Analogous behavior was observed in the aldol-type reaction of N-Boc α-amino aldehydes50. The temperature-dependent erosion of the ee is attributed to partial racemization of the chiral aldehyde (Supplementary Table S2). High diastereoselectivity (>20:1 dr) and excellent enantioselectivity (>90% ee) were consistently observed for other N-Boc α-amino aldehydes, yielding products 7b and 7c. The protocol also proved effective in carbohydrate chemistry, converting galactopyranose-derived aldehydes into complex glycosylated amino acid derivatives (7e-7g) and glycopeptide 7h with high diastereoselectivity. Consistent with the α-amino aldehyde results, significant substrate-induced diastereocontrol was observed, allowing for high selectivity even without the chiral catalyst. The absolute and relative configuration of 7g was unambiguously determined by single-crystal X-ray analysis. Furthermore, the methodology was successfully applied to peptide synthesis—a critical area in chemical biology and medicinal chemistry51—by employing N-formyl amino esters or peptides. This approach generated a series of dipeptides (7i-7m) in good to excellent yields (65–90%) with high levels of stereoselectivity (89-90% ee for achiral formyl glycinate; 87–88% de for chiral N-formyl amino esters). The method proved compatible with diverse amino acid side chains, as exemplified by glycine (7i, 7j), valine (7k), leucine (7l) and tert-leucine (7m). Notably, for these substrates, the diastereoselectivity appeared to be primarily governed by the chiral catalyst rather than the substrate’s stereocenter (7a-7h), likely due to the greater distance between the existing chiral center and the reacting prochiral imine (Please see Supplementary Information for details, Page S52). This strategy was readily extended to tripeptide synthesis, furnishing derivatives 7n-7r with high diastereoselectivities (74–90% de) using N-formyl dipeptides as precursors.

The practical utility and scalability of our protocol were demonstrated by conducting the synthesis of α-amino amides 4a and 4z on 1.0 mmol scale, achieving good yields (70 (64)% and 68%, respectively) and high enantioselectivities (94 (84)% and 93% ee) (Fig. 5a). Albeit with slightly lower yield and ee, a significant improvement in reaction efficiency was realized in flow (e.g., 1 mmol scale of 4a prepared in around 3.8 h in flow vs. 72 h in batch). Importantly, these amide products could be efficiently converted into the valuable free α-amino acids. For instance, 4a and 4z underwent a two-step sequence involving oxidative removal of the aryl amine moiety using TCCA/HCl52, followed by tert-butylamide hydrolysis with 6 M HCl, to afford the corresponding free amino acids 8 (95% yield, 91% ee from 4a; 90% yield from 4z) with minimal erosion of stereochemical integrity. Furthermore, the method readily facilitates the incorporation of isotopic labels (Fig. 5b). Using ¹⁵N-labeled aniline (9) yielded the ¹⁵N-containing amino amide 10 with excellent conversion and high enantioselectivity (88% ee). Access to α-deuterated derivatives was demonstrated using D₁-3-phenylpropanal, providing D₁-6s in 67% yield and 89% ee. Showcasing compatibility with in situ generated substrates, D₁₁-cyclohexanecarbaldehyde—prepared via TBADT-photocatalyzed carbonylation53,54 of D₁₂-cyclohexane under CO atmosphere and light irradiation—was directly utilized in the three-component reaction to furnish the heavily deuterated product D₁₁-4a (16%, >99% ee). These results underscore the methodology’s robustness, scalability, and adaptability for preparing structurally diverse and isotopically labeled amino acid derivatives.

Proposed mechanism
To gain insight into the reaction mechanism, several control experiments were conducted (Fig. 5c–f). Subjecting cyclopropanecarbaldehyde (2b) to the standard conditions afforded the corresponding α-amino amide 11 in 65% yield, with no evidence of cyclopropane ring-opening. This suggests that the reaction likely proceeds via the addition of a relatively nucleophilic radical intermediate55, avoiding intermediates prone to inducing ring-opening. The involvement of radical species was further substantiated by adding the radical scavenger TEMPO (1.0 equiv) to the standard reaction involving cyclohexanecarbaldehyde 2a. This resulted in a significantly decreased yield of the desired product 6a (34%) and the detection by HRMS of the TEMPO adduct of the carbamoyl radical (12) as well as the adduct (13) derived from trapping the subsequent α-amino radical intermediate formed after C-C bond formation. Conversely, species 14, potentially arising from single-electron reduction of the imine intermediate, was not detected. Additionally, light on/off experiments demonstrated that product formation ceased in the dark and resumed upon re-irradiation, confirming the reaction’s dependence on light energy and suggesting a photocatalytic process rather than a self-sustaining radical chain mechanism (Fig. 5d). We conducted an experiment to investigate the relationship between the ee of Na[5b] and the ee of product 4a. A linear correlation was observed, suggesting that a single molecule of the Na[5b] catalyst is involved in the enantio-determining step (Fig. 5e). Based on these experimental findings and relevant literature56–59, we propose a plausible catalytic cycle (Fig. 5f). Initially, visible light excitation of the photocatalyst TBADT (PC) generates its excited state (PC*). This excited state abstracts a hydrogen atom (HAT) from formamide 1 to produce the key carbamoyl radical intermediate (I) and the reduced form of photocatalyst (PC-H). Concurrently, aldehyde 2 and amine 3 reversibly condense to form imine II. The chiral sodium phosphate catalyst (Na[5c]) then coordinates to, activates and stabilize imine II, setting the stage for the enantioselective addition of the carbamoyl radical I. This forms a transient α-amino radical species which, upon subsequent oxidation (likely involving PC-H regenerating PC) and protonation, yields the final α-amino amide product 4 and finishes the catalytic cycle. We propose transition state TS-3 to describe the enantioselective addition of carbamoyl radical I. The chiral sodium phosphate catalyst plays a multifunctional role: (i) Na⁺ acts as a Lewis acid to activate the imine intermediate; (ii) Na⁺ stabilizes the transition state via cation–π interactions; and (iii) the P=O moiety serves as a hydrogen bond acceptor for the formamide N–H, which increases electron density on the nitrogen and thereby enhances the nucleophilicity of the carbamoyl radical. This proposed hydrogen bonding interaction is supported by the observation that formamides derived from secondary amines, which lack the N–H bond, failed to yield the desired products (see Supplementary Information, pages S54 and S69).

Methods
General procedure for the synthesis of chiral amino acid derivatives
A flame-dried 10 mL Schlenk tube was charged with aniline 3 (0.125 mmol, 2.5 equiv), TBADT (0.0045 mmol, 9 mol%), and (R)-Na[5c] (0.010 mmol, 20 mol%). The vessel was subjected to three cycles of evacuation and backfilling with N2. Then, MeCN, DCM, 1 (0.05 mmol, 1.0 equiv), and 2 (0.1 mmol, 2.0 equiv) were added. The resulting mixture was frozen in liquid nitrogen, and the headspace was evacuated. The resulting solution was stirred under LED (390 nm 40 W) at −78°C for 48 h. After completion, the mixture was removed from irradiation and concentrated under reduced pressure. Purification by silica gel chromatography (petroleum ether/ethyl acetate) afforded the target products.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In this manuscript, Han, Gong and co-workers have reported an enantioselective photochemical method for direct synthesis of chiral α-amino amides from simple aldehydes, amines, and formamides by integrating TBADT HAT catalyst and a chiral sodium phosphate as a dual catalytic system. The multi-component strategy circumvents pre-functionalization steps, marking a notable advance in asymmetric amide synthesis. This dual catalytic enantioselective study is well-conceived and operationally simple, demonstrating good substrate scope, including α,β-diamino acids, glycosylated derivatives, and peptides. The clarification regarding mechanistic insights and the role of each catalyst in enantioinduction would further enhance the impact and understanding of the study. Overall, the work represents a significant contribution to asymmetric catalysis and photoredox chemistry. The reviewer recommends for the publication after the following points are addressed.\nPoints to be addressed:\n(1) The screening data of chiral Brønsted acid 5c should be provided in the optimization table.\n(2) The aromatic aldehydes are not used in this study. The authors should comment on the omission of such coupling partner in this study. The comment should be added to the manuscript.\n(3) Formamides derived from primary amines have successfully been used in this study. However, the reviewer is curious to know whether formamides derived from secondary amines could also be used. The results or comment should be added to the manuscript.\n(4) The linearity test should be conducted, plotting ee of product vs ee of catalyst.\n(5) In this study, sodium salt of chiral Brønsted acid is performing better than the chiral acid. While acid can activate better the imine intermediate and lower LUMO energy for subsequent nucleophilic radical addition than sodium salt, nevertheless, the outcome seems to be reverse. “The hydrogen atom of the formamide group in the primary amine engages in hydrogen bonding with the imine, generating a partially positively charged iminium ion that forms an ion pair with the chiral phosphate. Simultaneously, the partial negative charge developed on the formamide nitrogen may enhance the radical-philicity of the nucleophilic radical.” The authors should check such possibilities.\n(6) In this supporting information, 13C NMR spectral data should be reported as single digit after point decimal, like d = 148.9 ppm, instead of d = 148.90 ppm.\n(7) The signal-to-noise ration is high in 13C NMR of following compounds. The 13C NMR for the same should be remeasured and better spectra should be reported.", "reviewer_2": "The manuscript by Gong and Han et al. describes a dual photoredox and chiral Brønsted acid-catalyzed three-component reaction for the synthesis of enantiomerically enriched α-amino amides from formamides, aldehydes, and anilines. The methodology is notable for its broad substrate scope, high enantioselectivities, and impressive applications in the synthesis of complex molecules, including peptides and isotopically labeled compounds. The mechanistic investigations provide solid evidence for the proposed pathway. This work represents a significant and practical advance in the field of asymmetric synthesis, offering a modular and efficient route to valuable chiral building blocks from simple feedstocks. I recommend publication in Nature Communications following minor revisions that will serve to clarify a few points and strengthen the overall discussion.\nMajor Strengths of the Manuscript\n1. Practicality and High Utility: The use of readily available and inexpensive starting materials—formamides, aldehydes, and amines—makes this methodology highly attractive and practical. The ability to convert the products to free α-amino acids with minimal erosion of stereochemical integrity further underscores its synthetic value.\n2. Broad Substrate Scope: The authors have conducted an extensive investigation of the reaction scope, successfully demonstrating its applicability to over 80 examples. The method tolerates a wide variety of substituents on the formamide, aniline, and aldehyde components, including those with functional groups useful for further elaboration.\n3. Excellent Stereocontrol: The dual catalytic system generally provides exceptional levels of enantioselectivity (up to 98% ee) and, where applicable, high diastereoselectivity.\n4. Impressive Synthetic Applications: The extension of this methodology to the synthesis of complex targets, such as α,β-diamino acids, glycosylated amino acids, and di- and tripeptides, is a major strength of this work and highlights its potential impact in medicinal chemistry and chemical biology.\nPoints for Revision The manuscript is well-written and the experiments are thoroughly executed. The following points are intended to further enhance the clarity and impact of the manuscript.\n1. Novelty and Conceptual Advance: The primary criticism one might have is that the work combines two well-known catalyst classes. While the individual catalysts (TBADT for HAT and chiral phosphates for enantiocontrol) are indeed established, their synergistic application in this specific three-component radical addition is novel and highly effective. To preempt this critique, I suggest the authors add a sentence or two to the introduction to more explicitly frame the conceptual advance. For instance, they could highlight the challenge of merging a radical HAT cycle with a stereocontrolling ionic or H-bonding activation manifold for this multicomponent transformation.\n2. Role of the Sodium Cation: The authors propose that the sodium cation plays a role in \"Lewis acid activation\" of the imine. While this is a plausible hypothesis supported by the screening of different counterions, the manuscript would be strengthened by a brief discussion of alternative or complementary roles. For instance, could the authors comment on the function of the chiral phosphate primarily as a chiral counterion that organizes the radical and the imine in the transition state through ion pairing? A brief mention of this possibility would provide a more complete mechanistic picture without requiring new experimental data.\n3. Substrate Control vs. Catalyst Control: The authors astutely observe a high degree of substrate control in the synthesis of α,β-diamino acids (e.g., syn-7a), where high diastereoselectivity is achieved even without the chiral catalyst. This is an interesting and important finding. To improve the narrative, I suggest the authors expand this discussion slightly to more explicitly contrast these cases with others (e.g., the peptide couplings 7i-7r) where catalyst control appears to be the dominant factor. This would offer readers a more nuanced understanding of the stereocontrol elements at play across the full scope of the methodology.\n4. Enantioselectivity with Primary Formamide: A minor clarification would be helpful regarding the observation that the primary formamide (leading to product 4b, 73% ee) provides lower enantioselectivity than various N-alkyl formamides (e.g., 4a, 96% ee; 4c, 85% ee). A brief mechanistic rationale, perhaps related to differences in steric interactions or the potential for hydrogen bonding in the transition state, would be beneficial for the reader.\n5. Efficiency of Flow Chemistry: The use of flow chemistry is presented as a key feature for broadening substrate tolerance. The data in the Supporting Information (p. 51-52) also indicates a significant improvement in reaction efficiency and throughput (e.g., 1 mmol of 4a prepared in 150 minutes in flow vs. 72 hours in batch). This is a powerful advantage, and I recommend the authors highlight this improved productivity more explicitly in the main text when discussing the scalability of the reaction.\nIn summary, this manuscript presents a highly valuable and broadly applicable method for the asymmetric synthesis of α-amino amides. The work is comprehensive, and the results are of high quality and impact. The minor points raised above are intended to further strengthen the manuscript's clarity and discussion. I am confident the authors can address these points satisfactorily, and I recommend the manuscript for publication in Nature Communications.", "reviewer_3": "In this manuscript, Gong and colleagues report a photocatalytic multicomponent protocol that combines aldehydes, primary amines, and formamides to furnish a variety of non-natural chiral α-amino acid derivatives. The reaction exhibits good enantioselectivity, a broad substrate scope, and good functional-group tolerance. Various synthetic utilities are also demonstrated, including up-scale reactions, the construction of other synthetically valuable scaffolds, and the use of flow chemistry, further highlighting the robustness of this methodology. Overall, this represents a useful approach for the preparation of non-natural α-amino acids from readily available starting materials, and it should be of interest to the readership of Nature Communications.\nSeveral key points, however, still need to be addressed. In the Introduction section, the authors mention current methods for the preparation of chiral amino acids, such as glycine alkylation via phase-transfer catalysis. In fact, many recent studies have reported glycine alkylation through bimetallic cooperative catalysis (e.g., Pd/Cu systems), which should be cited here.\nIn the Optimization section, the loading of the photocatalyst TBADT appears to be quite high. Would reducing the catalyst loading result in a significant loss of efficiency?\nWhile the substrate scope is impressively broad, the structure of the formamide exerts a significant influence on the enantioselectivity. In addition, the presence of a free proton seems to be essential. How does the enantioselectivity behave when secondary formamides are employed?\nThe extension of this methodology to peptide derivatives is particularly interesting. However, the efficiency and stereoselectivity in this case appear modest. In addition, the authors employ a superstoichiometric amount of peptide formamide, which is not commercially available and requires multistep synthesis. (The Supplemental Information does not provide the synthetic procedure; it is recommended that the authors include it.) Furthermore, can the peptide formamide be recovered after the reaction? These limitations reduce the overall attractiveness of the method. Further optimization of this section, ideally using peptide amides as the limiting reagent, would therefore be valuable.\nFinally, preliminary mechanistic studies are provided, confirming the involvement of a carbamoyl radical intermediate. Nevertheless, the reaction system contains two distinct acyl C–H bonds. The reaction appears to selectively undergo hydrogen-atom transfer (HAT) from the formamide rather than the aldehyde. Did the authors observe any HAT processes from the aldehyde? The origin of this high selectivity should be clarified.\nSome Minor Points:\nSome references are missing page and volume numbers, such as Ref. 17.\nFor the HPLC trace of compound 4ac, the integration of the chiral trace may be incorrect. The minor peak should appear at 5.17 min, and the authors are advised to re-examine this result.\nMost of the NMR spectra are clean; however, some compounds (7n, 7o, 7q, 7r) display noticeable ethyl acetate solvent peaks."}, "author_response": "Response: We sincerely thank the reviewer for the positive evaluation of our work and for the constructive comments. We have addressed each point as detailed below.\nPoints to be addressed:\n(1) The screening data of chiral Brønsted acid 5c should be provided in the optimization table.\nResponse: We thank the reviewer for this suggestion. We have now included the screening data\nfor chiral Brønsted acid 5c in the optimization table (Table 1, entry 15). The results show a\ndiminished yield but similar enantioselectivity (67% yield, 95% ee; entry 15 vs. entry 14).\nDetailed results are provided in the revised manuscript and also presented below:\n(2) The aromatic aldehydes are not used in this study. The authors should comment on the\nomission of such coupling partner in this study. The comment should be added to the manuscript.\nResponse: We appreciate the reviewer's comment. We have now evaluated benzaldehyde as an\naromatic aldehyde substrate under the current catalytic conditions, which afforded the desired\nproduct in moderate yield (46%) but with low enantioselectivity (37% ee). This result suggests\nthat aromatic imines are not well-suited for the reaction, likely due to their distinct electrophilicity\nand stability compared to aliphatic imines. These findings have been added to the revised\nmanuscript and the Supporting Information (page S53). Detailed results are shown below:\n(3) Formamides derived from primary amines have successfully been used in this study. However,\nthe reviewer is curious to know whether formamides derived from secondary amines could also be\nused. The results or comment should be added to the manuscript.\nResponse: We thank the reviewer for raising this point. Our experiments indicate that formamides\nderived from secondary amines (e.g., DMF) are not viable substrates in the current catalytic\nsystem. When 25 equiv. of DMF was used, no product derived from the carbamoyl radical was\ndetected; instead, a by-product arising from an alkyl radical was observed. This is likely because\nthe C–H bonds of the methyl groups in DMF can also undergo HAT, competing with and\nsuppressing carbamoyl radical formation (calculated BDEs of DMF: H–CO, 94.7 kcal/mol; trans-\nC–H, 94.0 kcal/mol; cis-C–H, 93.9 kcal/mol; J. Org. Chem. 2013, 78, 5909–5917). Similar\nobservations have been reported previously (Org. Lett. 2023, 25, 7014–7019). Additionally, the\nacidic N–H bond in primary formamides may form a hydrogen bond with the P=O moiety of the\ncatalyst, rendering the carbamoyl radical more nucleophilic. Formamides derived from secondary\namines lack this N–H bond and therefore cannot benefit from this \"reactivity enhancement\" effect.\nThese results have been added to the revised manuscript and Supporting Information (page S54).\n(4) The linearity test should be conducted, plotting ee of product vs ee of catalyst.\nResponse: We thank the reviewer for this suggestion. We conducted experiments to investigate\nthe relationship between the ee of the catalyst Na[5b] and the ee of product 4a. A linear correlation\nwas observed, suggesting that a single molecule of Na[5b] is involved in the enantiodetermining\nstep. These results have been added to the revised manuscript and the Supporting Information\n(page S67). Detailed results are shown below:\n(5) In this study, sodium salt of chiral Brønsted acid is performing better than the chiral acid.\nWhile acid can activate better the imine intermediate and lower LUMO energy for subsequent\nnucleophilic radical addition than sodium salt, nevertheless, the outcome seems to be reverse.\n“The hydrogen atom of the formamide group in the primary amine engages in hydrogen\nbonding with the imine, generating a partially positively charged iminium ion that forms an ion pair with\nthe chiral phosphate. Simultaneously, the partial negative charge developed on the formamide\nnitrogen may enhance the radical-philicity of the nucleophilic radical.” The authors should check\nsuch possibilities.\nResponse: We appreciate the reviewer's insightful comment. We agree that hydrogen bonding\ninvolving the formamide N–H plays an important role in this transformation. However, given the\nweak acidity of the formamide N–H, we consider it unlikely to generate a sufficiently stable\niminium ion for the chiral phosphate to consistently act as a counter anion throughout the reaction\nprocess. Instead, we propose that the formamide N–H forms a hydrogen bond with the P=O\nmoiety of the chiral catalyst, which enhances the nucleophilicity of the carbamoyl radical. This\nproposed hydrogen bonding interaction is supported by the observation that formamides derived\nfrom secondary amines, which lack the N–H bond, failed to yield the desired products\nBased on reported literature (Science 2018, 360, 419–422; ChemCatChem 2024, 16,\ne202400328) and our experimental observations, we propose three transition states: TS-1\n(background reaction without catalyst), TS-2 (with chiral phosphoric acid), and TS-3 (with chiral\nsodium phosphate). We attribute the superior performance of the sodium salt to the following\nfactors:\ni) The Lewis acidity of Na⁺ can activate the imine intermediate; ii) Na⁺ stabilizes the transition\nstate via cation–π interactions (ChemCatChem 2024, 16, e202400328); iii) The P=O moiety serves\nas a hydrogen bond acceptor for the formamide N–H, enhancing the nucleophilicity of the\ncarbamoyl radical.\nThese have been added to the revised manuscript.\n(6) In this supporting information, 13C NMR spectral data should be reported as single digit after\npoint decimal, like d = 148.9 ppm, instead of d = 148.90 ppm.\nResponse: We thank the reviewer for pointing this out. We have revised the 13C NMR spectral\ndata to report chemical shifts with one digit after the decimal point throughout the Supporting\nInformation.\n(7) The signal-to-noise ration is high in 13C NMR of following compounds. The 13C NMR for\nthe same should be remeasured and better spectra should be reported.\nResponse: We sincerely appreciate the reviewer for the constructive comments. We checked all\nthe 13C NMR, 4b, 6u, 6ad, 7c, 7d, 7n, 7o, 7q, 7r were remeasured and better spectra were\nreported in the revised Supporting Information.\nResponse: We are grateful for the reviewer's positive assessment of our work and the constructive\nsuggestions. We have addressed each point as detailed below.\nThe following points are intended to further enhance the clarity and impact of the manuscript.\n1. Novelty and Conceptual Advance: The primary criticism one might have is that the work\ncombines two well-known catalyst classes. While the individual catalysts (TBADT for HAT and\nchiral phosphates for enantiocontrol) are indeed established, their synergistic application in this\nspecific three-component radical addition is novel and highly effective. To preempt this critique, I\nsuggest the authors add a sentence or two to the introduction to more explicitly frame the\nconceptual advance. For instance, they could highlight the challenge of merging a radical HAT\ncycle with a stereocontrolling ionic or H-bonding activation manifold for this multicomponent\ntransformation.\nResponse: We sincerely appreciate the reviewer for the constructive comments. We have added\nthe following sentence to the introduction to highlight the conceptual advance: ‘Herein, we report\na dual catalytic system that integrates a HAT-mediated carbamoyl radical generation with a\nstereocontrolled ionic and H-bonding activated asymmetric addition between carbamoyl radical\nand an in situ formed imine. This strategy enables rapid and modular assembly of α-amino amides\nfrom readily available aldehydes, amines, and formamides (Fig. 1f). We sort out the cumulative\nchallenges that compatibility among the individual species in the reaction mixture (catalysts,\nsubstrates, intermediates), side reactions, catalyst deactivation, realization of broad substrate\nscope. The developed protocol affords a wide range of α-amino amide derivatives (>80 examples)\nwith up to >99% yield and >99% enantioselectivity.’ Please see our revised manuscript for details.\n2. Role of the Sodium Cation: The authors propose that the sodium cation plays a role in \"Lewis\nacid activation\" of the imine. While this is a plausible hypothesis supported by the screening of\ndifferent counterions, the manuscript would be strengthened by a brief discussion of alternative or\ncomplementary roles. For instance, could the authors comment on the function of the chiral\nphosphate primarily as a chiral counterion that organizes the radical and the imine in the transition\nstate through ion pairing? A brief mention of this possibility would provide a more complete\nmechanistic picture without requiring new experimental data.\nResponse: We sincerely appreciate the reviewer for the constructive comments. We propose\ntransition state TS-3 to describe the enantioselective addition of carbamoyl radical I. The chiral\nsodium phosphate catalyst plays a multifunctional role: (i) Na⁺ acts as a Lewis acid to activate the\nimine intermediate; (ii) Na⁺ stabilizes the transition state via cation–π interactions; and (iii) the\nP=O moiety serves as a hydrogen bond acceptor for the formamide N–H, which increases electron\ndensity on the nitrogen and thereby enhances the nucleophilicity of the carbamoyl radical. This\nproposed hydrogen bonding interaction is supported by the observation that formamides derived\nfrom secondary amines, which lack the N–H bond, failed to yield the desired products Please see\nthe response ( Reviewer #1, comment 5), our revised manuscript and Supporting Information page\nS69 for details.\n3. Substrate Control vs. Catalyst Control: The authors astutely observe a high degree of substrate\ncontrol in the synthesis of α,β-diamino acids (e.g., syn-7a), where high diastereoselectivity is\nachieved even without the chiral catalyst. This is an interesting and important finding. To improve\nthe narrative, I suggest the authors expand this discussion slightly to more explicitly contrast these\ncases with others (e.g., the peptide couplings 7i-7r) where catalyst control appears to be the\ndominant factor. This would offer readers a more nuanced understanding of the stereocontrol\nelements at play across the full scope of the methodology.\nResponse: We thank the reviewer for this suggestion. We have expanded the discussion in the\nmanuscript to contrast the cases of substrate control (e.g., 7a–7h) and catalyst control (e.g., 7i–7r).\nFor 7a–7h, the high diastereoselectivity is governed by the substrate's stereocenter (see Supporting\nInformation, page S38). In contrast, for 7i–7r, the diastereoselectivity is primarily controlled by\nthe chiral catalyst, as the existing chiral center is too remote to exert significant influence. We\nconfirmed this by measuring the de values of 7k, 7l, 7n, and 7p in the absence of the chiral\ncatalyst at 25 ℃, which showed low substrate control and the de decreased with increasing\ndistance. See Supporting Information for details (see Supporting Information, page S52) and\ndetailed results were also presented below (Ar1, 4-bromo-3,5-dimethylphenyl):\nWe expanded the discussion and added in the manuscript as below: Notably, for these\nsubstrates, the diastereoselectivity appeared to be primarily governed by the chiral catalyst rather\nthan the substrate's stereocenter (7a-7h), likely due to the greater distance between the existing\nchiral center and the reacting prochiral imine.\n4. Enantioselectivity with Primary Formamide: A minor clarification would be helpful regarding\nthe observation that the primary formamide (leading to product 4b, 73% ee) provides lower\nenantioselectivity than various N-alkyl formamides (e.g., 4a, 96% ee; 4c, 85% ee). A brief\nmechanistic rationale, perhaps related to differences in steric interactions or the potential for\nhydrogen bonding in the transition state, would be beneficial for the reader.\nResponse: We sincerely appreciate the reviewer's constructive comment. We attribute this trend\nprimarily to differences in steric interactions in the transition state. As demonstrated by products\n4a–4e, enantioselectivity increases with the steric bulk of the N-substituent on the formamide. The\nsmaller N–H group in primary formamide provides less effective steric differentiation between the\ntwo prochiral faces of the imine, resulting in lower enantiocontrol. This observation has been\nclarified in the revised manuscript.\n5. Efficiency of Flow Chemistry: The use of flow chemistry is presented as a key feature for\nbroadening substrate tolerance. The data in the Supporting Information (p. 51-52) also indicates a\nsignificant improvement in reaction efficiency and throughput (e.g., 1 mmol of 4a prepared in 150\nminutes in flow vs. 72 hours in batch). This is a powerful advantage, and I recommend the authors\nhighlight this improved productivity more explicitly in the main text when discussing the\nscalability of the reaction.\nResponse: We sincerely appreciate the reviewer for the constructive comments. The volume of the\nflow system was 10 mL and the velocity of liquid was 0.66 mL/min. The reaction time of each\nliquid segment was around 150 min. And 1 mmol scale reaction (15 mL solution) taken around\n227 min. We highlight this improved productivity more explicitly and revised the time in SI and\nmanuscript. Please see our revised manuscript for details: Albeit with slightly lower yield and ee, a\nsignificant improvement in reaction efficiency was realized in flow (e.g., 1 mmol scale of 4a\nprepared in around 3.8 h in flow vs. 72 h in batch).\nIn summary, this manuscript presents a highly valuable and broadly applicable method for the\nasymmetric synthesis of α-amino amides. The work is comprehensive, and the results are of high\nquality and impact. The minor points raised above are intended to further strengthen the\nmanuscript's clarity and discussion. I am confident the authors can address these points\nsatisfactorily, and I recommend the manuscript for publication in Nature Communications.\nResponse: We sincerely thank this reviewer for the favorable comments on our work.\nResponse: We sincerely thank the reviewer for the positive comments and valuable suggestions.\nWe have addressed each point as detailed below.\nSeveral key points, however, still need to be addressed. In the Introduction section, the authors\nmention current methods for the preparation of chiral amino acids, such as glycine alkylation via\nphase-transfer catalysis. In fact, many recent studies have reported glycine alkylation through\nbimetallic cooperative catalysis (e.g., Pd/Cu systems), which should be cited here.\nResponse: We thank the reviewer for this suggestion. We have now cited recent studies on glycine\nalkylation via Pd/Cu synergistic catalysis (J. Am. Chem. Soc. 2025, 147, 20359–20371; Science\n2024, 385, 972–979) in the revised manuscript.\nIn the Optimization section, the loading of the photocatalyst TBADT appears to be quite high.\nWould reducing the catalyst loading result in a significant loss of efficiency?\nResponse: We thank the reviewer for this comment. As shown in Table S1 (Supporting\nInformation, page S2), reducing the TBADT loading to 6 mol% resulted in a slight decrease in\nyield (80% vs. 93% with 9 mol%) without affecting enantioselectivity. We therefore selected 9\nmol% TBADT as the optimal loading. The results are summarized below:\nConditions Yield % ee %\nwith 9 mol% TBADT 93 38\nwith 6 mol% TBADT 80 37\nwith 12 mol% TBADT 92 36\nWhile the substrate scope is impressively broad, the structure of the formamide exerts a significant\ninfluence on the enantioselectivity. In addition, the presence of a free proton seems to be essential.\nHow does the enantioselectivity behave when secondary formamides are employed?\nResponse: We thank the reviewer for this comment. As noted in our response to Reviewer #1,\ncomment (3), secondary formamides (e.g., DMF) did not yield the desired products. This is likely\ndue to competing HAT from the N-alkyl groups and the absence of the N–H bond, which we\npropose enhances the nucleophilicity of the carbamoyl radical via hydrogen bonding with the\ncatalyst. Consequently, enantioselectivity data for secondary formamides could not be obtained.\nThe extension of this methodology to peptide derivatives is particularly interesting. However, the\nefficiency and stereoselectivity in this case appear modest. In addition, the authors employ a\nsuperstoichiometric amount of peptide formamide, which is not commercially available and\nrequires multistep synthesis. (The Supplemental Information does not provide the synthetic\nprocedure; it is recommended that the authors include it.) Furthermore, can the peptide formamide\nbe recovered after the reaction? These limitations reduce the overall attractiveness of the method.\nFurther optimization of this section, ideally using peptide amides as the limiting reagent, would\ntherefore be valuable.\nResponse: We sincerely appreciate the reviewer for the constructive comments.\nPeptide formamides for the reaction:\nN-Formyl amino acid esters: sub-7i, sub-7j, sub-7k, sub-7l and sub-7m were commercially\navailable from ‘Energy-Chemical’ and ‘Bidepharm’ companies. sub-7n-r were prepared from the\nfollowing synthetic procedure:\nThe revised SI provided the synthetic procedure and NMR spectra. Please see our revised\nSupporting Information page S44 for details.\nMaterial Recovery:\nWe have conducted the material recovery experiment as shown above. About 87% of the\nunreacted peptide formamide sub-7q was recovered.\nPeptide amides as the limiting reagent:\nWe also attempted to use peptide formamide as the limiting reagent (e.g., sub-7q). However,\ndue to the low reactivity of sub-7q at –78 °C, an excess was required to maintain sufficient\nconcentration for efficient HAT. When sub-7q was used as the limiting reagent (0.1 mmol) under\nstandard conditions, product 7q was obtained in only 28% yield (90% de). Further optimization\n(longer reaction time, varying equivalents, and elevated temperature) did not improve the yield,\nand raising the temperature led to a significant decrease in diastereoselectivity. Therefore, an\nexcess of peptide formamide is currently necessary to achieve acceptable diastereoselectivity.\nFinally, preliminary mechanistic studies are provided, confirming the involvement of a carbamoyl\nradical intermediate. Nevertheless, the reaction system contains two distinct acyl C–H bonds. The\nreaction appears to selectively undergo hydrogen-atom transfer (HAT) from the formamide rather\nthan the aldehyde. Did the authors observe any HAT processes from the aldehyde? The origin of\nthis high selectivity should be clarified.\nResponse: We thank the reviewer for this insightful comment.\nObservation of HAT from the aldehyde:\nAs shown below, when the reaction was performed at 25 oC with excess aldehyde, byproduct\narised from the addition of acyl radical (from the aldehyde) could be observed. Only trace amount\nof the by-product was detected under our standard conditions (-78 ℃, aldehyde : aniline = 0.1 :\n0.125).\nOrigin of the high selectivity:\nDuring our optimization process, we found that using excess aniline accelerates imine\nformation, which consumes the aldehyde and suppresses acyl radical generation. Meanwhile, the\ncarbamoyl radical accumulates and undergoes rapid addition to the imine. Thus, the high\nselectivity arises from the reaction stoichiometry rather than intrinsic differences in HAT rates.\nSome Minor Points:\nSome references are missing page and volume numbers, such as Ref. 17.\nResponse: We sincerely appreciate the reviewer for the constructive comments. We have checked\nand corrected all references, including Ref. 17, 34, and 35.\nFor the HPLC trace of compound 4ac, the integration of the chiral trace may be incorrect. The\nminor peak should appear at 5.17 min, and the authors are advised to re-examine this result.\nResponse: We sincerely appreciate the reviewer for the constructive comments. We re-examined\nthe HPLC of asymmetric 4ac. We also revised the ee of 4ac in SI and manuscript.\nMost of the NMR spectra are clean; however, some compounds (7n, 7o, 7q, 7r) display noticeable\nethyl acetate solvent peaks.\nResponse: We have remeasured the NMR spectra for 7n, 7o, 7q, and 7r and now provide\nimproved spectra in the Supporting Information.\nWe sincerely thank all the reviewers for their time and valuable comments, which have\nsignificantly improved the quality of our manuscript."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have addressed most of the comments from this reviewers.\nHowever, the reviewer have not seen the example of aromatic aldehyde derived product in substrate scope table in manuscript, although it is added to the supporting information. The HPLC chromatogram for the same is missing.\nThe supporting information that reviewer received has no page numebering.\nThe manuscript can be accepted once these minor corrections are made.", "reviewer_2": "The authors have satisfactorily addressed my previous comments, and the manuscript is now clearer and more compelling.\nThe Introduction better highlights the conceptual novelty of combining HAT-mediated carbamoyl radical generation with a stereocontrolled ionic/H-bonding activation manifold in a multicomponent system. The expanded mechanistic discussion, including the TS model for the chiral sodium phosphate and its multiple roles, provides a more comprehensive rationale for the observed selectivities. The comparison between substrate-controlled and catalyst-controlled stereochemistry across different product classes is now clearly documented, and the discussion of reduced enantioselectivity with primary formamides is reasonable and consistent with the reported data. In addition, the flow chemistry section has been clarified with precise information on reactor volume, residence time, and productivity, appropriately emphasizing the practical advantages over batch conditions. I have no further substantive concerns, and I recommend publication after minor editorial polishing.", "reviewer_3": "Author has addressed all of reviewer's comments well, I think this paper is now suitable for publication in NC as it is."}, "author_response": "Response to Reviewers’ Comments\nReviewer #1:\nThe authors have addressed most of the comments from this reviewer. However, the reviewer have\nnot seen the example of aromatic aldehyde derived product in substrate scope table in manuscript,\nalthough it is added to the supporting information. The HPLC chromatogram for the same is\nmissing. The supporting information that reviewer received has no page numebering. The\nmanuscript can be accepted once these minor corrections are made.\nResponse: We thank the reviewer for the constructive feedback. Per your comments, the example\nof the aromatic aldehyde–derived product (labeled as Ar‑TM) has been added to the substrate\nscope (Fig. 3) in the manuscript, and the corresponding HPLC chromatogram is now included in\nthe Supporting Information (page S249), which has been updated with full page numbering.\nReviewer #2:\nThe authors have satisfactorily addressed my previous comments, and the manuscript is now\nclearer and more compelling. The Introduction better highlights the conceptual novelty of\ncombining HAT-mediated carbamoyl radical generation with a stereocontrolled ionic/H-bonding\nactivation manifold in a multicomponent system. The expanded mechanistic discussion, including\nthe TS model for the chiral sodium phosphate and its multiple roles, provides a more\ncomprehensive rationale for the observed selectivities. The comparison between substrate-\ncontrolled and catalyst-controlled stereochemistry across different product classes is now clearly\ndocumented, and the discussion of reduced enantioselectivity with primary formamides is\nreasonable and consistent with the reported data. In addition, the flow chemistry section has been\nclarified with precise information on reactor volume, residence time, and productivity,\nappropriately emphasizing the practical advantages over batch conditions. I have no further\nsubstantive concerns, and I recommend publication after minor editorial polishing.\nResponse: We are very grateful to the reviewer for their supportive feedbac. We appreciate the\nreviewer’s time and constructive comments, which have helped strengthen the manuscript. We\nhave carefully proofread the manuscript to ensure it meets the journal's editorial standards.\nReviewer #3:\nAuthor has addressed all of reviewer's comments well, I think this paper is now suitable for\npublication in NC as it is.\nResponse: We sincerely thank the reviewer for the positive evaluation and recommendation for\npublication.\nWe sincerely appreciate the reviewers’time and thoughtful comments, which have been\ninstrumental in improving the manuscript. We are also grateful for their positive assessment and\nrecommendation for publication."}]

Decision letter