Dedicated to a peptide chemist of few words and immense impact: Louis A. Carpino

Abstract

This issue of Peptide Science is a testimonial to brilliance packaged in a nontraditional way. We are honoring the contributions of Louis A. Carpino (“Lou” to many of us or “Louie” to a few), who passed away in January 2019 at the age of 91. Lou Carpino's contributions to peptide chemistry specifically, and organic chemistry more broadly, over the course of his career are truly stunning as summarized in the articles in this collection. Yet he pursued his work quietly and on his own terms, eschewing the usual accolades and attention that would come to one whose work is so influential. The compilation of papers in this issue constitutes a testament to the impact of Lou Carpino's research. However, the articles are only representative as there is little in the peptide chemistry field that has not been enabled and touched by the genius and chemical virtuosity of Lou Carpino. In addition to the research articles collected here, we have also gathered brief “In Memoriam” pieces from a number of Lou's colleagues. These pieces paint a fuller picture of Lou Carpino the mentor, Lou Carpino the teacher, and—to a small extent—Lou Carpino the father. A master of compartmentalization, Lou Carpino was for each of us only one thread of a complex fabric. We hope that this issue will give a better picture of the full fabric of Lou Carpino and, in so doing, reflect the masterful chemist and multifaceted human being he was. The field of peptide chemistry is richer for his stellar career-long contributions and poorer for the passing of this gentle and passionate man. Lou Carpino was born in 1927 in Des Moines, IA (U.S.A.). He took his academic position at the University of Massachusetts at Amherst in 1954 after completing his doctoral work at the University of Illinois with Harold R. Snyder and a short postdoctoral stint at the University of South Carolina with DeLos F. Detar. He published his first independent paper based on work at UMass Amherst in 1956, and many other single-author papers followed shortly. These were harbingers of the abundant and significant publications emanating from Lou Carpino's lab. Lou Carpino remained at UMass Amherst for his entire 65-year career, active until shortly before his death. We begin this issue with editorial pieces reflecting several aspects of Lou Carpino's career. First, we reprint an obituary written by Lou Carpino's longtime collaborator, Michael Beyermann. Lou Carpino worked for many years in a three-way collaboration with Michael Beyermann and Michael Bienert, and was also joined in this collaboration by Holger Wenschuh, then a graduate student. We include touching comments about the scientific partnership from Holger Wenschuh. Following these comments is a short piece by one of us (Fernando Albericio) putting Lou Carpino's contributions to peptide chemistry in perspective. Additional pieces from Ayman El-Faham, Khaled Nasr and Salvatore “Sal” Triolo, all of whom were trainees with Lou Carpino, and Peter Lillya, a longtime faculty colleague of Lou Carpino's at UMass, paint a picture of Carpino the teacher and mentor. Another of the co-editors (Lila Gierasch) offers additional thoughts on Lou Carpino as a colleague and friend, including brief comments about his family. A detailed commentary from the third co-editor (Claudio Toniolo) emphasizing Lou's scientifically very productive 6-month stay at his Institute in Padua in the late 1960s can be found in the Introduction of a paper in this special issue (C. Toniolo, A. Moretto, F. Formaggio, Q. B. Broxterman and M. Crisma, Pept. Sci. 2020, 112, e24153). Following the introductory material to this issue are several articles contributed by members of the peptide chemistry community. These illustrate how greatly this community values the work of Lou Carpino and how peptide chemistry is enabled by the landmark achievements Carpino made to protecting groups and coupling reagents. Please read the articles and realize as you do how much of the work in the peptide field, currently and over the past 50 years, could not have happened without the contributions of Lou Carpino. We hope that this issue of Peptide Science stands as a testament to a spectacular career and that, more importantly perhaps, it reveals and shines light on a scientist who chose to stay away from the limelight while he passionately pursued his research. We also hope that you will get to know Lou Carpino better than you may have had the chance to while he was alive, sadly. Lila M. Gierasch1 Fernando Albericio2,3 Claudio Toniolo4 1Departments of Biochemistry & Molecular Biology and Chemistry, University of Massachusetts, Amherst, Amherst, U.S.A. 2School of Chemistry, University of KwaZulu-Natal Durban, South Africa 3Department of Organic Chemistry, University of Barcelona Barcelona, Spain 4Department of Chemistry, University of Padua and Institute of Biomolecular Chemistry, Padua Unit, CNR, Padua, Italy Special Collections & University Archives The University of Massachusetts Amherst A treasure trove of material from Louis A. Carpino's career has been archived in the Special Collections of the University of Massachusetts Amherst library archives. It is available as an invaluable resource chronicling the intellectual path through peptide chemistry followed by this giant of our field. Among the items that have been archived are over 20 notebooks kept by Louis Carpino from the time he started his research. They are written in his own hand and describe his thinking and creative experimental design, which led to the products he has offered the field. We urge anyone interested to avail themselves of this material through a visit to the University campus in Amherst. Please make a virtual visit to the archives in the meantime at: http://scua.library.umass.edu/umarmot/carpino-louis-a/. Louis A. Carpino (1927-2019) Dr Louis A. Carpino (91) passed away at home in Amherst, MA, on Friday, January 4, 2019. He was a Professor Emeritus of Organic Chemistry at the University of Massachusetts Amherst. Dr L. A. Carpino was a pioneer in the development of amino-protecting groups and coupling reagents for use in the synthesis of biologically active materials such as pharmaceuticals, polynucleotides, peptide nucleic acids (PNAs), peptides, and small proteins. His first significant contribution was the development of the tert-butyloxycarbonyl (Boc) group as a protecting group for amino acids.[1] With its much greater acid lability than the benzyloxycarbonyl-(Z) protecting group, the Boc group facilitated the synthesis of peptides. The discovery of the Boc group enabled a new strategy in the synthesis of peptides. The Boc strategy combined the use of a Boc group as a temporary Nα-amino protecting group with the much more acid-stable, permanent side chain benzyl-based protecting groups. Boc amino acids are mostly crystalline, easily prepared using a number of synthetic methods, and stable even at room temperature. In general, activation and coupling of Boc amino acids to the N-terminus of growing peptides is carried out with no side reaction. Because of the rapid removal of Boc groups by TFA/DCM, HCl/dioxane or other acids, Boc amino acids were found to be particularly suited for the development of and use in solid-phase peptide synthesis (SPPS) created by R. B. Merrifield in 1963.[2] Boc protection of amino acids has been highly successful in the syntheses of a limited number of proteins and is compatible with automated machines and for parallel synthesis of a large number of short peptides (on pins or in “tea bags”). Dr Carpino's next major accomplishment addressed a weak point in the use of Boc-protecting groups, especially in the presence of other acid labile-protecting groups. While the temporary Boc group can be removed under much milder conditions than the permanent groups, the latter groups are not completely stable following repeated Boc removals. Thus, partial side-chain deprotection during the synthesis of long peptides in SPPS may yield undesired side products and complex crude products. Moreover, the final deprotection of side chain functionalities, as well as cleavage of peptide from resin in the Boc strategy, necessitates the use of harsh conditions, such as liquid hydrogen fluoride, which may lead to modification/degradation of the product by side reactions, including aspartimide formation, N/O-shift, etc. Dr Carpino developed a completely orthogonal-protecting system using the 9-fluorenylmethoxycarbonyl (Fmoc) group.[3] The Fmoc-protecting group is removed rapidly and efficiently by proton abstraction via secondary amines, conditions that do not affect acid-labile tert-butyl-type protecting groups placed on the side chains. Moreover, the Fmoc group is completely stable under the conditions used for removal of the resin linkers. Fmoc amino acids are generally easy to prepare in crystalline form and stable during storage. Fmoc amino acids can be highly activated and efficiently coupled without side reactions, and their high ultraviolet (UV) absorption makes it possible to monitor their incorporation during the assembly of the peptide. By using the secondary amines such as piperidine to remove the Fmoc group, the dibenzofulvene formed is trapped on the spot, minimizing possible side reactions. The Fmoc-based SPPS is currently the method of choice for the chemical synthesis of peptides. Dr Carpino developed several other protecting groups that have also found widespread application. The benzothiophenesulfone-2-methyloxycarbonyl (Bsmoc)-protecting group is an example of a large new class of protecting groups that can be removed under the very mild conditions of Michael addition.[4] The 2,2,4,6,7-pentamethyldihydrobenzofuran-5-sulfonyl group (Pbf) was developed for side chain protection of arginine and is easily removed by trifluoroacetic acid (TFA). Pbf can be used efficiently in the synthesis of arginine-containing peptides.[5] The icyclopropylmethyl (Dcpm) group is used in polypeptide syntheses when it is necessary to minimize peptide insolubility and aggregation.[6] In the case of threonine/serine-containing peptides, an alternative route to avoid aggregation problems involves the synthesis of the corresponding O-acyl-peptide isomers and subsequent rearrangement back to regular peptides after synthesis and purification.[7] In addition to his seminal contributions around amino-protecting groups, Dr Carpino developed several new types of coupling reagents based on acid halides and 1-hydroxy-7-azabenzotriazole that are far more efficient than classical reagents because of their speed, generality, and control of epimerization. Fmoc-amino acid fluorides have facilitated efficient SPPS of peptaibols, such as alamethicin, the synthesis of which was previously reported via a laborious solution-phase route.[8] The more reactive Fmoc-amino acid chlorides, although being less stable than the corresponding fluorides, enable the coupling of extremely hindered systems, such as N-methyl-amino-iso-butyric acid to amino-iso-butyric acid.[9] Finally, uronium/guanidinium compounds of 1-hydroxy-7-azabenzotriazole (HOAT) are very efficient activation reagents,[10] although their recent use, especially in large-scale syntheses, has been limited for safety reasons. Dr Carpino's contributions over a long and distinguished career have enabled synthetic peptide chemistry as it is widely practiced today. Dr Carpino never stopped thinking about the design of better coupling reagents. In fact, he was working on a new coupling reagent to address some of the safety issues with HOAT over the past year when he passed away. Dr Carpino was born in Des Moines, Iowa, on December 13, 1927. He was a loving husband, father, and grandfather and is survived by his wife, Barbara, and six children. I got to know him as a great teacher, creative director who shared his ideas, attentive listener who showed respect for anyone, a quiet person who shunned the great arena but fostered intense scientific collaboration over many years. He touched the lives of many people—he will be missed. Michael Beyermann Longtime collaborator of Louis Carpino Markkleeberg, Germany [1] L.A. Carpino, J. Am. Chem. Soc. 1957, 79, 4427. [2] R. B. Merrifield, J. Am. Chem. Soc. 1963, 85, 2149. [3] L. A. Carpino, G.Y. Han, J. Am. Chem. Soc. 1970, 92, 5748. [4] L. A. Carpino, M. Ismail, G. A. Truran, E. M. E. Mansour, S. Iguchi, D. Ionescu, A. El-Faham, C. Riemer, R. Warrass, J. Org. Chem. 1999, 64, 4324. [5] L. A. Carpino, H. Shroff, S. A. Triolo, E. M. E. Mansour, Tetrahedron Lett. 1993, 34, 7829. [6] L. A. Carpino, K. Nasr, A. A. Abdel-Maksoud, A. El-Faham, D. Ionescu, P. Henklein, H. Wenschuh, M. Beyermann, E. Krause, M. Bienert, Org. Lett. 2009, 11, 3718. [7] L. A. Carpino, Krause E, C. D. Sferdean, M. Schümann, H. Fabian, M. Bienert, M. Beyermann, Tetrahedron Lett. 2004, 45, 7519. [8] L. A. Carpino, M. Beyermann, H. Wenschuh, M. Bienert, Acc. Chem. Res. 1996, 29, 68. [9] L. A. Carpino, D. Ionescu, A. El-Faham, P. Henklein, H. Wenschuh, M. Bienert, M. Beyermann, Tetrahedron Lett. 1998, 39, 241. [10] L. A. Carpino, H. Imazumi, A. El-Faham, F. J. Ferrer, C. Zhang, Y. Lee, B. M. Foxman, P. Henklein, C. Hanay, C. Mügge, H. Wenschuh, J. Klose, M. Beyermann, M. Bienert, Angew. Chem. Int. Ed. 2002, 41, 441. Louis A. Carpino (1927-2019) Michael Beyermann J. Pept. Sci. 2019, 25, e3168; John Wiley and Sons, Ltd © 2019 European Peptide Society and John Wiley & Sons, Ltd. Reprinted with permission of Wiley Publishing, Ltd. In 1990, when I started my Ph.D. work at the East-German Institute for Molecular Pharmacology in Berlin, only a few months after the Berlin Wall collapsed, Louis Carpino had an ongoing collaboration with our research team. This was unusual because the beginning of that fruitful relationship dated back to the time when the institute still worked under the strict East German regulations. When Louis and his lovely wife Barbara visited Berlin and the institute early in 1991, he asked whether I could imagine coming to the United States to do part of my thesis work in his laboratories at the University of Massachusetts at Amherst. As a young East German scientist I was of course full of excitement and applied for a grant at the German Academic Exchange Service. Almost nine months later, on January 6, 1992, Louis and Barbara picked me up at Bradley Airport in Hartford, Connecticut, and gave me a ride to Amherst. The following seven months under Louis' mentorship became some of the most influential of my entire academic and business career. Louis A. Carpino's research team in 1992 [Reprinted with permission of the University of Massachusetts Chemistry Department.] We started a variety of projects exploiting the full impact of protected amino acid fluorides for solid phase peptide synthesis, their suitability for incorporating extremely sterically hindered amino acids into peptides, for the assembly of biologically active peptaibols, and more. During that time I witnessed Louis' outstanding ability to manage a multinational scientific team with members from eight countries and varying cultural backgrounds. He was not only always open to new ideas and visions but he actively supported all of us by sharing his profound knowledge of peptide chemistry, including how to structure scientific work in a systematic and goal-oriented way. His capacity to listen with respect for everyone and to motivate every single team member, especially after setbacks, was inspiring and gave me guidance throughout my business career. My first visit to Louis“lab was not the last. Only one year later a grant from Perseptive Biosystems supported by Fernando Albericio brought me back to Louis' lab for another couple of months. This was like coming home. During my academic career—post-docing at the Max Planck Institutes in Germany; joining JERINI AG, a peptide drug company; and finally establishing JPT Peptide Technologies in Berlin—we continued to have an active scientific and personal exchange. Louis and Barabara's annual visits to Berlin were always among the highlights of the year and felt like family reunions. Over the years we were able to co-publish more than 30 peer-reviewed papers, short communications and book chapters. Louis' passing in 2019 was an incredible loss for the peptide science community and me. His countless contributions to modern peptide science laid the foundation for many of the most recent breakthrough applications using thousands of peptides in proteomics and immunotherapy. Every single day we continue to apply and improve the knowledge Louis Carpino created and shared over the decades for the sake of developing advanced therapeutic options for meeting medical needs. Holger Wenschuh Collaborator and visiting scientist with Louis Carpino Managing Director, JPT Peptide Technologies GmbH, 12489 Berlin, Germany My colleague Louis Carpino I met Prof. Carpino when I was appointed Director of Peptide Research at Millipore-Waters near Boston, U.S.A., in 1991. My first relation with him in this position was rather bizarre for two scientists from academia (I was on leave from the University of Barcelona, Spain, where I held a position as Associate Professor, and where I returned in 1994 to continue my academic career). In this regard, we were brought together to negotiate the commercialization rights of the new coupling reagents based on the 7-aza-1-hydroxybenzotriazole (HOAt), the proper HOAT, the aminium salt (HATU), and the phosphonium salt (PyAOP) that we had jointly developed between the two groups.[1] In addition, Prof. Carpino was deeply interested in Millipore-Waters exploring the commercialization of the Bsmoc protecting group. According to him, Bsmoc was superior to Fmoc. Prof. Carpino and the University of Massachusetts (UMass) were represented by Research Corporation Technologies (RCT), a company based in Tucson, AZ. I first met the General Director of RCT on a cold winter morning in Medford, MA, and I remember that he brought me copies of most of Prof. Carpino's papers to show me who exactly this scientist was in the peptide world and the importance of having good coupling reagents and versatile protecting groups. At the end of our meeting, the director of RCT realized and acknowledged that I knew more about Prof. Carpino and his work than he did. As you may imagine, we quickly reached an agreement, and I hope both Prof. Carpino and UMass took away good memories of their relations with Millipore-Waters. However, there is no doubt that those who most benefited from that agreement were the members of the peptide community. Indeed, thanks to the agreement, reagents and derivatives such as HOAt, HATU, PyAOP, TFFH, and Fmoc-Arg(Pbf)-OH were, and still are, available to us. Unfortunately, and after intense efforts of several companies, including Millipore-Waters, Perceptive Biosystems, which later acquired the rights of the agreement with UMass, and finally the Collins family at CEM, the Bsmoc/Nsmoc-amino acids are no longer a reality. On a more personal note, I consider Prof. Carpino a mentor from whom I received several “gifts.” In addition to his scientific advice, I had the privilege of meeting his excellent students. Prof. Ayman and I first started our collaboration under the umbrella of Prof. Carpino and then continued it independently. This collaboration has spanned almost 30 years, and following Prof. Carpino's scientific interests, we developed OxymaPure. I also met Dr Fernando Ferrer-Gago, who is currently in Singapore, and with whom I still collaborate. Furthermore, two of Prof. Carpino's former students, namely, Dr Hitesh Schroff, who developed the Pbf group, and Dr Salvatore Triolo, joined my group at Millipore-Waters. All Prof. Carpino's students were extraordinary scientists, and they reflect the qualities of the great man himself. Louis Carpino, an extraordinary peptide chemist One can name three Nobel Prize winners who had a profound impact on the peptide field: Emil Fisher (Nobel Prize in Chemistry in 1902),[1] Vincent Du Vignaud (1955),[2] and R. Bruce Merrifield (1984).[3] Yet while these scientists made seminal contributions, they could not be considered organic chemists, and thus, their work did not touch the mechanistic realities of peptide synthesis. In the peptide arena, the two key organic chemists were Leonidas Zervas and Louis A. Carpino. The former was responsible for introducing the concept of the “masking group”, more commonly known as protecting group. Zervas' idea was that the group should hide the reactivity of a given functional organic group.[4] Later, after modification of other parts of the molecule, the protecting group would then be removed, releasing the functional group of interest. Louis Carpino took this concept one step further as he recognized that to be useful a protecting group had to be removable, and that protecting group removal must take place under mild conditions to ensure the integrity of the peptide product.[5] Throughout his career in peptide chemistry, Carpino was centered on, or better said, “absorbed” by reactions under mild conditions, reaction yields, and the purity of the compounds synthesized. This focus clearly reflects the organic chemist's way of thinking and contrasts with that of the biochemist, who is usually more interested in obtaining the molecule, although some penalties have to be paid. As peptide chemists, we can thank our lucky stars that this was the focus of Carpino's career because it led to many synthetically powerful groups and reactions that have moved the peptide field in key ways. Although Carpino developed chemistry for the solution phase, his achievements were rapidly transferred to solid-phase chemistry. With respect to Solid-Phase Peptide Synthesis (SPPS), two strategies are always mentioned, namely tert-butoxycarbonyl (Boc)/benzyl (Bzl) and fluorenylmethoxycarbonyl (Fmoc)/tert-butyl (tBu). Interestingly, both are based on Boc and Fmoc, two α-amino protecting groups developed by Carpino. The former was published in 1960,[6] while the latter came about in 1970 while Carpino was searching for protecting groups removable in mild conditions.[7] The Boc group was rapidly adopted by Merrifield for the synthesis of bradykinin, published in 1964[8] [In his seminal 1963 JACS paper, Merrifield used benzyloxycarbonyl (Z, named by Zervas), which requires HBr-AcOH to be removed in solid phase.][3] For the Fmoc group, in 1978, and independently Meienhofer[9] in the U.S.A. and Sheppard and Atherton[10] in Europe, developed a mild SPPS strategy, namely Fmoc/tBu. As illustrated in an article of this issue of Peptide Science, Carpino's work on protecting groups went far beyond Boc and Fmoc.[11] In the field of α-amino protecting groups, he devoted much effort fine-tuning both protecting groups. However, his most significant contribution to this field was the development of a new family of α-amino protecting groups, which are removed through a Michael addition reaction. The most representative example of this family is 1,1-dioxobenzo[b] thiophene-2-yl)methyloxycarbonyl (Bsmoc).[12] According to Carpino Bsmoc showed several advantages over Fmoc, but as was reported above Bsmoc amino acids have never reached the market. The most intriguing amino acid side chain to protect is probably the guanidino function of Arg. There is current consensus that the protecting group of choice is 2,2,4,6,7-pentamethyldihydrobenzofuran-5-sulfonyl group (Pbf), developed by Carpino.[13] Fmoc-Arg(Pbf)-OH is commercially available and is by far the most widely used Arg derivative in SPPS. Taking advantage of the facile solvolysis of the cyclopropylmethyl substrates, Carpino developed protecting groups based on that moiety for the carboxylic group (dicyclopropylmethyl, Dcpm) and for the amide side chain of Asn and Gln (dimethylcyclopropyl, Dmcp).[14] He extended the concept used for the side chain of Asn/Gln for backbone protection, with the aim of preventing intra-chain and inter-chain aggregations, which are the main events responsible for the formation of deletion peptides.[15] With the same objective, namely, the prevention of chain interactions, Carpino—in collaboration with the group of his long-term collaborators Professors Bienert and Beyermann, and in parallel to Professor Kiso's work in Japan[16]—proposed the elongation of Ser and Thr in the peptide chain through the β-hydroxy function of these amino acids (ester bond), thereby impeding hydrogen bond formation between chains.[17] Once the depsipeptide is synthesized and purified, the ester bond is converted to the peptide in basic medium. Carpino was also a visionary in terms of High-Throughput Peptide Synthesis, and in 1983 he developed piperazino- and piperidino-functionalized solid supports for the rapid and clean removal of the Fmoc group in solution.[18,19] A few years later, he established rapid Continuous Solution-Phase Peptide Synthesis for the preparation of peptides with up to 22 amino acids based on the use of the tris(2-aminoethyl)amine for Fmoc removal.[20] The key to this strategy is the use of an aqueous buffer to remove the byproducts arising from the reaction of dibenzofulvene with the secondary amine and the amine itself. As stated in one of the contributions to this issue,[11] peptide synthesis is often defined as the proper combination of protecting groups and coupling reagents. With this definition in mind, Carpino covered all peptide synthesis. In the first part of his scientific career he worked mainly on the development of protecting groups, while in the second part he described the second generation of coupling reagents.[21] Using the current terminology adopted in the context of green chemistry, we can say that Carpino pursued the use of “minimalist” activating strategies, characterized by acceptable impact in terms of atom economy and very high performance. Thus he gave a second opportunity to acyl halides (chlorides and fluorides) as a coupling method.[22] In the case of the latter, which is more compatible with the tBu side chain protecting groups used in the Fmoc methodology, he developed the first stand-alone coupling reagent (tetramethylfluoroformamidinium hexafluorophosphate, TFFH), which in situ forms the corresponding acid fluorides.[23] Compatible with even the carbodiimide chemistry, benzyltriphenylphosphonium dihydrogen trifluoride (PTF) was developed by Carpino as an additive for the formation in situ of the acid fluoride using carbodiimides.[24] The main contribution of Carpino to this field was probably the development of the chemistry based on 7-aza-1-hydroxybenzotriazole (HOAt),[25] which has been shown to greatly outperform, in both solid-phase and solution chemistry, 1-hydroxybenzotriazole (HOBt) in terms of enhancing coupling yields and reducing racemization. From HOAt, the corresponding stand-alone reagents, N-[(dimethylamino)-1H-1,2,3-triazolo[4,5-b] pyridin-1-ylmethylene] -N-methylmethanaminium hexafluorophosphate N-oxide (HATU)[25] and [(7-azabenzotriazol-1-yl)oxy] tris(pyrrolidino) phosphonium hexafluorophosphate (PyAOP),[26] were obtained. These reagents are considered the most efficient in both the solid phase and solution phase for the acylation of highly hindered N-terminal residues. These include α,α-dialkyl-substituted and N-alkyl amino acids. These reagents have shown excellent performance for the cyclization step in the synthesis of cyclic peptides. Like any good scientist, Carpino showed enormous curiosity. Although he had chemically rationalized the superiority of HOAt vs HOBt (the presence of the N in position 7 of the aromatic system had a classic neighboring group effect on the incoming amine moiety), he was greatly surprised by the immense superiority of HATU vs its corresponding HOBt derivative, HBTU. From the first description of HBTU, this family of compounds was assigned to uronium salts, where the “O” of the benzotriazole unit was linked to a “C.” In an attempt to understand the distinct reactivity of HATU and HBTU, Carpino crystallized them and demonstrated that neither reagent was a uronium salt, but rather, they were aminium salts, where the link between the two moieties was through a bond between “N” of the benzotriazole and the “C”.[27] He later went on to synthesize and crystallize a “true” uronium salt.[28] This discussion of Louis Carpino's contributions to peptide synthetic chemistry is offered to underscore what a virtuoso genius he was and the breadth of his impact. Fernando Albericio Longtime collaborator of Louis Carpino School of Chemistry, University of KwaZulu-Natal, Durban, South Africa [1] F. E. Fischer, Ber. Dtsch. Chem. Ges. 1901, 34, 2868. [2] V. d. Vigneaud, C. Ressler, C. J. M. Swan, C. W. Roberts, P. G. Katsoyannis, S. Gordon, J. Am. Chem. Soc. 1953, 75, 4879. [3] R. B. Merrifield, J. Am. Chem. Soc. 1963, 85, 2149. [4] Z. L. Bergmann, Ber. Dtsch. Chem. Ges. 1932, 65B, 1192. [5] L. A. Carpino, Accounts Chem. Res. 1973, 6, 191. [6] L. A. Carpino, J. Am. Chem. Soc. 1960, 82, 2725. [7] L. A. Carpino, G. Y. Han, J. Am. Chem. Soc. 1970, 92, 5748. [8] R. B. Merrifield, J. Am. Chem. Soc. 1964, 86, 304. [9] C.-D. Chang, J. Meienhofer, Int. J. Pep. Prot. Res. 1978, 11, 246. [10] E. Atherton, H. Fox, D. Harkiss, C. J. Logan, R. C. Sheppard, B. J. Williams, J. Chem. Soc, Chem. Comm. 1978, 537. [11] A. A. El-Faham, F. Albericio, Pept. Sci. 2020, 112, e24164. [12] L. A. Carpino, M. Philbin, M. Ismail, G. A. Truran, E. M. E. Mansour, S. Iguchi, D. Ionescu, A. El-Faham, C. Riemer, R. Warrass, M. S. Weiss, J. Am. Chem. Soc. 1997, 119, 9915. [13] L. A. Carpino, H. Shroff, S. A. Triolo, E. S. M. E. Mansour, H. Wenschuh, F. Albericio, Tetrahedron Lett. 1993, 34, 7829. [14] L. A. Carpino, H. G. Chao, S. Ghassemi, E. M. E. Mansour, C. Riemer, R. Warrass, D. Sadat-Aalaee, G. A. Truran, H. Imazumi, H. Wenschuh, M. Beyermann, M. Bienert, H. Shroff, F. Albericio, S. A. Triolo, N. A.