The Methodological Value of HATU in Difficult Couplings: Reactivity Advantages, Stereochemical Retention, and Condition Management

1. The Value of HATU Lies Not Merely in High Reactivity, but in Its Methodological Advantages in Difficult Couplings

HATU[O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate] has long been used as a high-performance coupling reagent, but the real reason it merits separate discussion is not simply that reactions proceed faster. In couplings between ordinary carboxylic acids and ordinary amines, many reagent systems can accomplish bond formation. The real differences usually emerge in steps involving substantial steric hindrance, weakly reactive amine partners, more complex fragments, or higher demands on stereochemical retention. The experimental value of HATU is manifested mainly in such difficult couplings and stereochemically sensitive couplings, and it should not be reduced to a mere synonym for an “efficient coupling reagent.”

This positioning is based largely on studies of HOAt [1-hydroxy-7-azabenzotriazole] and related high-reactivity coupling systems. Work published in 1993 first showed that HOAt, used as a coupling additive, could significantly improve peptide bond formation efficiency, and this became an important foundation for the continued attention later given to systems such as HATU. A subsequent 1994 study on racemization control further showed that HOAt-related systems were more favorable than traditional benzotriazole-based systems for avoiding racemization in model solid-phase peptide synthesis. In other words, what truly makes HATU worth discussing on its own is not merely that it is “faster,” but that in some difficult couplings it has a better chance of converting its efficiency advantage into improved stereochemical outcomes.

1.1 Core Value and Positioning of HATU

Dimension of Focus	Core Judgment	Experimental Significance
Reactivity	The advantage of HATU is not merely faster reaction, but a greater likelihood of driving effective coupling for difficult substrates	Better suited for priority use in key difficult steps
Methodological value	The distinguishing features of HATU are more likely to emerge in systems with high steric hindrance, weak reactivity, complex fragments, or stereochemical sensitivity	Evaluation should focus on whether the difficult step is truly solved
Evaluation of results	One should not judge only by whether product is formed or whether the yield is acceptable	Reaction completion, stereochemical purity, and byproducts should also be assessed simultaneously
Selection logic	HATU is better viewed as a priority screening tool for highly challenging couplings, not the default answer for every coupling task	Reagent selection should be guided by substrate difficulty and stereochemical risk

2. Why High Reactivity Can Create an Opportunity for Better Stereochemical Retention

The key value of HATU is not simply that coupling is faster, but that faster coupling can, under certain conditions, improve stereochemical retention. For substrates prone to racemization or epimerization, the risk usually arises when the activated intermediate persists too long, when amine attack is too slow, when pre-activation is prolonged, or when the local basic environment is too strong. The importance of the HOAt [1-hydroxy-7-azabenzotriazole] system lies in the fact that it not only improves coupling efficiency, but is also more favorable for reducing the loss of stereochemical integrity. The 1994 study further showed that HOAt-related high-reactivity coupling systems were more advantageous than traditional benzotriazole-based systems in avoiding racemization in model solid-phase peptide synthesis.

It should be noted, however, that HATU is not a reagent that is “inherently free from racemization.” A more accurate understanding is that HATU often helps move the coupling more rapidly from the activation stage to the target amide, thereby shortening the time window during which certain side reactions can occur. Whether this efficiency advantage can ultimately be translated into better stereochemical retention still depends on the intrinsic sensitivity of the substrate, the identity and equivalents of the base, the pre-activation time, the solvent environment, and the rate of amine attack.

2.1 Why HATU Can Favor Stereochemical Retention

Process Step	Possible Change	Significance for the Stereochemical Outcome
Carboxylic acid activation	More ready formation of an activated intermediate suitable for subsequent attack	Reduces stagnation in which the substrate is “activated but not yet converted into product”
Amine attack	The amine captures the activated intermediate more quickly	Shortens the exposure time of the intermediate
Competition from side reactions	The time window for some racemization or epimerization pathways is compressed	Creates a better opportunity to improve stereochemical retention
Final outcome	Under suitable conditions, the efficiency advantage can be translated into a stereochemical advantage	This advantage is condition-dependent, not automatically guaranteed

3. In Which Experimental Situations Is HATU More Worth Prioritizing

The situations in which HATU most deserves priority in screening are usually not general amidation steps, but rather coupling tasks with higher demands on reaction completion, stereochemical outcome, and side-reaction control. The reason HOAt/HATU systems are regarded as high-performance coupling systems is that they more often show methodological advantages with complex or challenging substrates. From the standpoint of experimental decision-making, HATU is better suited for priority use with highly hindered substrates, fragment couplings, weakly reactive amine partners, and stereochemically sensitive key steps, rather than as a universal solution for all coupling reactions.

3.1 Experimental Situations in Which HATU Deserves Priority Screening

Experimental Situation	Why HATU Deserves Priority Consideration	Key Experimental Focus
Coupling involving highly hindered carboxylic acids or amines	Greater likelihood of driving the reaction to completion and reducing stagnation after activation but before bond formation	Focus on reaction completion, not only final yield
Fragment coupling or linkage of complex intermediates	High-performance systems are more likely to create a meaningful difference in key steps	Monitor stereochemical purity and byproducts simultaneously
Weakly reactive amine partner	The value of faster capture of the activated intermediate becomes more evident	Pay attention to pre-activation time and total reaction time
Stereochemically sensitive amide bond formation	Greater opportunity to convert coupling efficiency into better stereochemical retention	Monitor ee, de, or diastereomer ratio
Ordinary amidation with low steric hindrance	HATU may not be strictly necessary	More economical or milder systems may be compared in parallel

A representative case is provided by the synthesis of acidiphilamide A–C. After comparing multiple coupling conditions, the authors found that, in the key coupling between dipeptide 18 and L-phenylalaninol 13, the HATU/N,N-diisopropylethylamine/N,N-dimethylformamide (HATU/DIPEA/DMF) conditions gave a diastereomeric ratio of 96:4, outperforming the PyBOP, T3P, DCC, and EDC·HCl conditions compared in the study. One judgment can be drawn from this result: when a key coupling step faces pressure from both bond-forming efficiency and stereochemical outcome, HATU deserves priority inclusion in screening.

4. In Evaluating HATU, the Key Issue Is Not Reagent Strength, but Substrate and Condition Management

Highly sensitive substrates most clearly reveal the condition dependence of HATU-based systems. A 2012 study on the solid-phase synthesis of O-linked glycopeptides showed that many common peptide coupling conditions led to significant epimerization at the α position; in some reactions, the non-natural epimer even reached as high as 80% and became the major product. The study also indicated that the intensified epimerization of such substrates was related to faster epimerization kinetics, the greater thermodynamic favorability of the non-natural epimer, and the overall slower rate of coupling. In that system, the use of 2,4,6-trimethylpyridine (TMP) as the base afforded higher coupling efficiency and lower epimerization. This result shows that for substrates with a high risk of epimerization, a high-performance coupling reagent alone cannot automatically solve the stereochemical problem; substrate properties and reaction conditions still require independent optimization.

Evaluation of HATU systems should not stop at the question of “whether HATU was used,” but should instead focus on substrate and condition management. For highly sensitive substrates, what truly determines the result is whether the activated intermediate is captured in a timely manner and whether the reaction conditions amplify the risk of epimerization. Whether the advantages of HATU can genuinely be translated into improved stereochemical outcomes depends on factors such as pre-activation control, base selection, substrate sensitivity, the rate of amine capture, as well as temperature and order of addition. HATU is therefore better regarded as a high-performance coupling system that requires careful optimization, rather than a default answer that automatically suppresses risk.

4.1 Key Factors Affecting the Performance of HATU-Based Systems

Key Factor	Main Risk	Key Experimental Focus
Pre-activation time	Excessive pre-activation prolongs exposure of the activated intermediate, increasing the risk of racemization or epimerization	Limit pre-activation to what is needed for activation; do not prolong it mechanically
Base identity and equivalents	Overly strong base or excessive base loading may amplify side reactions or stereochemical changes	Adjust independently according to substrate sensitivity
Substrate epimerization liability	Highly sensitive substrates, such as glycosylated amino acids, are more prone to epimerization	Conventional coupling conditions should not be applied without scrutiny
Rate of amine capture	Slow amine capture can weaken the efficiency advantage of HATU	Consider whether the substrate pairing is well matched
Temperature and order of addition	Improper settings can prolong the lifetime of the activated intermediate	Key coupling steps should be controlled with precision

5. In Assessing the Safety of HATU, Genetic Toxicology Findings Should Be Distinguished from Occupational Exposure Risks

The safety assessment of HATU should not be simplified to “safer” merely because one toxicological result is negative. A 2016 study showed that HOAt [1-hydroxy-7-azabenzotriazole] and HATU were negative in the bacterial reverse mutation test (Ames test), meaning that they did not show mutagenicity at this specific genetic toxicology endpoint. This conclusion primarily indicates that HOAt and HATU are not mutagenic at that particular endpoint; however, it does not mean that the overall laboratory risk is low, nor does it justify disregarding occupational exposure risks.

For laboratory practitioners, occupational exposure risks deserve separate and explicit attention. A 2022 systematic assessment of the occupational health hazards of peptide coupling reagents pointed out that skin sensitization is a major risk for this class of chemicals. Of the 25 peptide coupling reagents tested, 21 were positive for skin sensitization, and 15 of these were classified as strong or extreme sensitizers. The study also indicated that highly reactive peptide coupling reagents of the type to which HATU belongs require particular attention with respect to occupational exposure, and that the associated adverse effects may involve both skin and respiratory symptoms. From this perspective, a negative Ames result speaks only to the outcome at a specific mutagenicity endpoint, whereas occupational exposure control, personal protective equipment (PPE), and ventilation management belong to another equally important dimension of safety assessment.

5.1 How to Understand the Scope of Applicability of Safety-Related Conclusions for HATU

Existing Conclusion	What the Conclusion Indicates	What Still Needs to Be Considered
HOAt and HATU are negative in the Ames test	This indicates that they did not show mutagenicity at this specific genetic toxicology endpoint	This does not replace assessment of actual exposure risks in the laboratory; day-to-day handling should still be evaluated comprehensively with regard to sensitization, irritation, and exposure control
Occupational health studies on peptide coupling reagents indicate sensitization and irritation risks	This indicates that this class of reagents may still pose occupational health hazards during handling and exposure	Even for classical and widely used reagents, PPE, ventilation, and standardized operating practices still require close attention

6. Product Navigation Table for Research on HATU in Difficult Couplings (Choose Table 1–Table 3 by Research or Experimental Goal)

Current Research or Experimental Goal	Which Table to Consult First	Why This Table Should Be Prioritized	Which Table to Consult Next	Selection Guidance
Want to first establish the basic conditions for HATU coupling and determine which reagent system to start with	Table 2	Table 2 brings together HATU and its most common high-reactivity comparison systems, making it the most suitable starting point for defining the range of core coupling reagents	Then Table 1	It is easier to build an initial set of directly testable conditions by first selecting the main coupling reagent and then pairing it with an appropriate solvent and tertiary amine base.
Want to compare the differences among HATU, HBTU, TBTU, HCTU, PyAOP, PyBOP, COMU, and TOTU	Table 2	Table 2 directly compiles high-reactivity uronium and phosphonium systems, making it the most suitable for head-to-head comparison among the main reagents	Then Table 1	When comparing main reagents, the solvent and base should usually be kept as consistent as possible so that the differences arising from the coupling reagent itself can be seen more clearly.
Want to handle highly hindered substrates, difficult-to-couple amino acids, or key fragment couplings	Table 2	Difficult couplings should first be approached from the standpoint of highly reactive main reagents; Table 2 is better suited for screening whether the key bond-forming step can be driven forward successfully	Then Table 1	After the main reagent has been selected, comparison of DMF, NMP, and DCM, together with DIPEA and NMM, often makes it easier to improve conversion.
Want to focus on racemization control, stereochemical retention, or the coupling behavior of stereochemically sensitive substrates	Table 3	Table 3 concentrates components such as HOAt, HOBt, Oxyma, K-Oxyma, DEPBT, and DMTMM, which are better suited for discussing low-racemization behavior and differences in activation pathways	Then Table 2	It is easier to judge how “high reactivity” and “stereochemical retention” are balanced by first looking at low-racemization additives and alternative systems, and then returning to high-reactivity systems such as HATU, COMU, and PyAOP for comparison.
Want to establish comparison routes based on DIC, DCC, or EDC·HCl combined with additives	Table 3	Table 3 places carbodiimide systems together with their common supporting additives, making it most suitable for constructing comparison conditions such as DIC/HOBt, DIC/Oxyma, and EDC·HCl/Oxyma	Then Table 1	Carbodiimide systems are often influenced by the medium and base, so subsequent consultation of Table 1 is more suitable for fine adjustment of solvent and acid scavenger base.
Want to compare the HATU route with non-benzotriazole alternatives such as CDI, EEDQ, and DMTMM	Table 3	In Table 3, CDI, EEDQ, and DMTMM represent activation modes different from HATU/HOAt and are suitable for establishing alternative reference routes	Then Table 2	It is easier to judge when stronger activation is needed and when a milder route is sufficient by first examining the alternative systems and then reviewing high-reactivity systems such as HATU, COMU, and PyAOP.
Want to study the effects of additives such as HOAt, HOBt, Oxyma, and K-Oxyma on coupling outcomes	Table 3	Table 3 brings together several of the most common additives for suppressing side reactions and reducing racemization, making direct additive-level comparison more convenient	Then Table 2	Additive screening usually needs to be considered together with the specific main coupling reagent, so after returning to Table 2 it becomes easier to judge which “main reagent + additive” combination is more reliable.
Want to optimize solvents, tertiary amine bases, and the reaction medium to see whether changing conditions can improve difficult couplings	Table 1	Table 1 focuses on components such as DMF, NMP, DCM, DIPEA, and NMM, which most directly influence the coupling environment	Then Table 2	When the main coupling reagent has already been tentatively identified, adjusting the medium and base first is often more efficient than blindly replacing the main reagent.
Want to move stepwise from traditional coupling systems to HATU-based systems and compare the extent of improvement	Table 3	In Table 3, DCC, DIC, EDC·HCl, CDI, and EEDQ are better suited as baseline references for traditional or alternative systems	Then Table 2	It is easier to see where the key improvements come from by first establishing a baseline with traditional systems and then switching to high-reactivity systems such as HATU, COMU, and PyAOP.
Want to design a first-round condition-screening plan for a new substrate without making the system too broad at the outset	Table 2	First-round screening usually starts from representative high-reactivity main reagents, and Table 2 is better suited as the entry point for initial screening	Then Table 1 and Table 3	A common approach is to first select one or two main reagents from Table 2, then fine-tune the solvent and base using Table 1, and, if necessary, add low-racemization additives or alternative activation systems from Table 3.

Table 1 | Reaction Media and Supporting Organic Bases

Category	CAS No.	Aladdin Catalog No.	Name	Specification or Purity	Product Features and Applications
Common polar aprotic solvent for coupling reactions	68-12-2	D119450	N,N-Dimethylformamide (DMF)	Anhydrous, ≥99.8%	One of the most commonly used polar media for peptide coupling; dissolves reagents such as HATU, HBTU, and COMU well, and is suitable for establishing standard conditions for difficult couplings and for comparison with NMP- and DCM-based systems.
Common high-boiling polar aprotic solvent for coupling reactions	872-50-4	M119668	1-Methyl-2-pyrrolidinone (NMP)	Anhydrous, ≥99.5%	A high-boiling polar medium commonly used for substrates requiring higher solubility or for solid-phase systems; also suitable for comparing the effects of solvent polarity and viscosity on coupling efficiency.
Tertiary amine acid scavenger / non-nucleophilic organic base	7087-68-5	D109322	N,N-Diisopropylethylamine	Distilled grade, ≥99.5%	One of the most commonly used tertiary amine bases in HATU, HBTU, PyAOP, and COMU systems; used to promote bond formation after carboxylic acid activation and to neutralize acid generated during the reaction.
Tertiary amine acid scavenger / milder organic base	109-02-4	M104643	N-Methyl morpholine	Distilled grade, ≥99.5%	More commonly used in DMTMM systems, some phosphonium reagents, or specific solid-phase systems; suitable for comparing the effects of different tertiary amine bases on activation rate and side reactions.
Common low-boiling comparison solvent for coupling reactions	75-09-2	D116155	Dichloromethane	Super dry, H₂O ≤0.004%, stabilized with 50–150 ppm amylene	A low-boiling solvent convenient for workup; commonly used as a comparison solvent in phosphonium or some solution-phase coupling condition screening, and also suitable for comparison with DMF and NMP in solvent-effect studies.

Table 2 | Core High-Reactivity Coupling Reagents and Classical High-Reactivity Comparison Systems

Category	CAS No.	Aladdin Catalog No.	Name	Specification or Purity	Product Features and Applications
HOAt-type activating additive / low-racemization-promoting component	39968-33-7	H109328	1-Hydroxy-7-azabenzotriazole	≥99%	Commonly used together with carbodiimide or uronium/phosphonium systems to accelerate activation and suppress epimerization; suitable for comparing the differences among HOAt, HOBt, and Oxyma additives.
HOAt-type uronium coupling reagent / core reagent for difficult couplings	148893-10-1	H109327	HATU	≥99%	Commonly used for establishing conditions for highly hindered substrates, N-methyl amino acids, or key fragment couplings; also suitable for comparing reactivity and stereochemical retention against HBTU, PyAOP, and COMU.
HOBt-type uronium coupling reagent / classical high-reactivity comparison reagent	94790-37-1	H106174	HBTU	≥99%	A classical HOBt-type high-reactivity reagent, often used as a direct comparator to HATU for evaluating how differences in leaving groups affect coupling rate and side-reaction control.
Chlorobenzotriazole-type uronium coupling reagent / enhanced-reactivity comparison reagent	330645-87-9	C106175	O-(6-Chlorobenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate	≥98%	The chlorobenzotriazole leaving group makes this reagent useful for examining how stronger activation affects the yield and epimerization level of difficult bond-forming steps.
Benzotriazole-type uronium coupling reagent / classical high-reactivity comparison reagent	125700-67-6	T109338	TBTU	≥98%	Commonly used for baseline condition screening in solution-phase or solid-phase couplings, and also suitable for comparison with HBTU and HATU in activation efficiency and side-reaction behavior.
Oxyma-type uronium coupling reagent / new-generation high-reactivity comparison reagent	1075198-30-9	C340003	COMU	≥98%	One of the Oxyma-type highly reactive reagents; commonly used for screening bulky junctions or microwave coupling conditions, and also suitable for comparing Oxyma and benzotriazole systems in low-racemization performance.
Oxyma-type uronium coupling reagent / alternative high-reactivity comparison reagent	136849-72-4	E102847	TOTU	≥98%	Often used as a supplementary control among Oxyma-type uronium reagents for comparing the efficiency and byproduct control of different Oxyma-based leaving groups in difficult couplings.
HOAt-type phosphonium coupling reagent / high-reactivity fragment-coupling reagent	156311-83-0	A109335	(7-Azabenzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate	≥97%	An HOAt-type phosphonium reagent commonly used for fragment couplings requiring high reactivity and good stereochemical retention; also suitable for comparison with HATU in phosphonium versus uronium systems.
HOBt-type phosphonium coupling reagent / classical high-reactivity comparison reagent	128625-52-5	P109336	1H-Benzotriazol-1-yloxytripyrrolidinophosphonium Hexafluorophosphate	≥98%	One of the classical phosphonium coupling reagents, often used for comparison with BOP, HBTU, and HATU to evaluate the effects of different cation frameworks and leaving-group combinations on coupling performance.
Classical phosphonium coupling reagent / historical comparison reagent	56602-33-6	B106161	BOP Reagent	≥98%	A classical early phosphonium coupling reagent suitable as a historical benchmark for comparing the efficiency and side-reaction behavior of newer HOAt-, Oxyma-, or triazine-based reagents.

Table 3 | Classical Activating Reagents, Low-Racemization Additives, and Alternative Systems

Category	CAS No.	Aladdin Catalog No.	Name	Specification or Purity	Product Features and Applications
Quinoline-type activating reagent / classical non-uronium comparison reagent	16357-59-8	E109326	2-Ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline	≥99%	Can be used to establish milder non-uronium activation conditions and is also suitable for comparing substrate compatibility under different activation modes versus HATU, DMTMM, and CDI.
Carbodiimide dehydrating coupling reagent / classical comparison reagent	538-75-0	D106074	N,N′-Dicyclohexylcarbodiimide	≥99%	One of the most classical dehydrating coupling reagents, commonly used together with HOBt or HOAt; suitable for comparing carbodiimide systems with HATU systems in efficiency and workup characteristics.
Imidazole-type carbonyl activating reagent / non-uronium comparison reagent	530-62-1	C109315	N,N'-Carbonyldiimidazole (CDI)	≥99%	Activates through an acyl imidazole intermediate; suitable for establishing non-benzotriazole reference systems and comparing the performance of milder activation with that of highly reactive uronium systems.
Carbodiimide coupling reagent / common comparison reagent in solid- and solution-phase synthesis	693-13-0	N420184	N,N'-Diisopropylcarbodiimide	≥98.5%	A commonly used carbodiimide reagent in both solid-phase and solution-phase coupling, often paired with HOBt, HOAt, or Oxyma for comparison of byproduct filterability and efficiency in difficult couplings.
Water-soluble carbodiimide / solution-phase comparison reagent	25952-53-8	E106172	N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride	≥98%	A water-soluble carbodiimide commonly used for screening amidation conditions in solution phase or aqueous/mixed-phase systems; also suitable for comparison with DIC and DCC in process convenience.
Oxime-type low-racemization additive / supporting component for carbodiimide systems	3849-21-6	E138773	Ethyl (hydroxyimino)cyanoacetate	≥98%	Commonly used together with DIC or EDC·HCl to improve coupling efficiency and reduce epimerization; also suitable for comparing Oxyma with HOBt and HOAt additives.
Low-racemization coupling reagent / stereochemical-retention comparison reagent	165534-43-0	D100524	3-(Diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3H)-one	≥98%	Known for relatively low epimerization; suitable for control screening with stereochemically sensitive substrates, racemization-prone sites, or fragment-coupling steps.
Benzotriazole activating additive / classical anti-racemization component	123333-53-9	H106176	1-Hydroxybenzotriazole Monohydrate	≥97%	One of the classical supporting additives for carbodiimide systems, used to suppress side reactions arising from intermediates such as O-acylisoureas, and also serves as a baseline for comparison among HOBt, HOAt, and Oxyma systems.
Triazine-type coupling reagent / non-benzotriazole alternative system	3945-69-5	D110326	4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride hydrate (DMTMM)	≥97%	A triazine-type coupling reagent commonly used for establishing amidation conditions in non-benzotriazole routes, and also suitable for comparing bond formation under different media and milder conditions.
K-Oxyma potassium salt additive / supporting low-racemization component	158014-03-0	K468794	K-Oxyma	≥97%	The potassium salt form of Oxyma is convenient for use with carbodiimide systems and is suitable for comparing how salt-form additives affect solubility, ease of addition, and low-racemization performance.

Note: The products listed above are representative Aladdin products. For additional product specifications, please refer to the product list at the end of the article or search by “product name/CAS/catalog number” on the Aladdin website.

References

[1] Carpino LA. 1-Hydroxy-7-azabenzotriazole. An efficient peptide coupling additive. J Am Chem Soc. 1993;115(10):4397–4398. doi:10.1021/ja00063a082.

[2] Carpino LA, El-Faham A, Albericio F. Racemization studies during solid-phase peptide synthesis using azabenzotriazole-based coupling reagents. Tetrahedron Lett. 1994;35(15):2279–2282. doi:10.1016/0040-4039(94)85198-0.

[3] El-Faham A, Albericio F. Peptide coupling reagents, more than a letter soup. Chem Rev. 2011;111(11):6557–6602. doi:10.1021/cr100048w.

[4] Nicolette J, Neft RE, Vanosdol J, Murray J. Peptide bond-forming reagents HOAt and HATU are not mutagenic in the bacterial reverse mutation test. Environ Mol Mutagen. 2016;57(3):236–240. doi:10.1002/em.21997.

[5] Graham JC, Trejo-Martin A, Chilton ML, et al. An evaluation of the occupational health hazards of peptide couplers. Chem Res Toxicol. 2022;35(6):1011–1022. doi:10.1021/acs.chemrestox.2c00031.

[6] Zhang Y, Muthana SM, Farnsworth D, Ludek O, Adams K, Barchi JJ Jr, Gildersleeve JC. Enhanced epimerization of glycosylated amino acids during solid-phase peptide synthesis. J Am Chem Soc. 2012;134(14):6316–6325. doi:10.1021/ja212188r.

[7] Mallesham P, Raghavulu K, Miriyala V, Doddipalla R, Yennam S, Sanasi PD, Behera M. Synthesis of Acidiphilamide A–C: Secondary metabolites from the genus Streptacidiphilus. SynOpen. 2023;7(1):130–139. doi:10.1055/a-2035-9753.

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