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Fumo VM, Roberts RC, Zhang J, O'Reilly MC. Diastereoselective synthesis of cyclic tetrapeptide pseudoxylallemycin A illuminates the impact of base during macrolactamization. Org Biomol Chem 2023; 21:1056-1069. [PMID: 36628602 PMCID: PMC11311250 DOI: 10.1039/d2ob02126a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Therapeutic agents with unique molecular structures and new mechanisms of action are needed to confront the phenomenon of multidrug resistance among bacteria. Pseudoxylallemycins, cyclic tetrapeptide (CTP) natural products, have exhibited modest antibiotic activity, but their synthesis has proven challenging. Inherent ring strain in CTPs decreases the rate of cyclization in lieu of polymerization and racemization pathways, which has resulted in previous syntheses describing mixtures of diastereomers containing predominantly an undesired epimer. We have optimized the cyclization step of pseudoxylallemycin A to favor production of the natural diastereomer; notably, variation of the base, temperature, and solvent with peptide coupling reagent propylphosphonic anhydride (T3P) afforded exquisite selectivity for the natural product in as high as 97 : 3 DR, and our conditions can provide the natural product in up to 32% overall yield through 8 steps. Employing weaker bases than those typically used in peptide coupling reactions led to the greatest improvement in diastereoselectivity, and these studies demonstrated that the identity of the amine base has enormous impact on the rate of C-terminal epimerization when T3P is used, a variable usually considered of lesser consequence when combined with typical amide coupling reagents. Toward fully characterizing pseudoxylallemycin stereoisomers, variable temperature NMR was described as a tool to more clearly analyze CTPs that exhibit multiple conformational states. These synthetic and spectroscopic insights were applied toward synthesizing several natural product analogues, and their antibacterial activity was examined using microdilution assays.
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Affiliation(s)
- Vincent M Fumo
- Department of Chemistry, Villanova University, 800 E Lancaster Ave, Villanova, Pennsylvania 19085, USA.
| | - R Charlie Roberts
- Department of Chemistry, Villanova University, 800 E Lancaster Ave, Villanova, Pennsylvania 19085, USA.
| | - Jieyu Zhang
- Department of Chemistry, Villanova University, 800 E Lancaster Ave, Villanova, Pennsylvania 19085, USA.
| | - Matthew C O'Reilly
- Department of Chemistry, Villanova University, 800 E Lancaster Ave, Villanova, Pennsylvania 19085, USA.
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Cameron AJ, Brimble MA, Park C, Howard GK, Harris PWR. Total Synthesis of Allene-Containing Cyclic Tetrapeptide Pseudoxylallemycin C. Synlett 2021. [DOI: 10.1055/a-1282-6870] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
AbstractThe first total synthesis of the allene-containing cyclic tetrapeptide pseudoxylallemycin C is reported. The Tyr(t-Bu)-protected linear peptide was prepared on-resin and cyclized in solution phase to yield the protected cyclic precursor. Upon deprotection of Tyr(t-Bu), the desired phenolic cyclic tetrapeptide was separated by RP-HPLC from its epimer that also formed during the macrocyclisation step. Subsequent alkylation with 4-bromobuta-1,2-diene yielded pseudoxylallemycin C.
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Affiliation(s)
- Alan J. Cameron
- School of Chemical Sciences, The University of Auckland
- School of Biological Sciences, The University of Auckland
- Maurice Wilkins Centre for Molecular Biodiscovery, The University of Auckland
| | - Margaret A. Brimble
- School of Chemical Sciences, The University of Auckland
- School of Biological Sciences, The University of Auckland
- Maurice Wilkins Centre for Molecular Biodiscovery, The University of Auckland
| | - Casey Park
- School of Chemical Sciences, The University of Auckland
- School of Biological Sciences, The University of Auckland
| | | | - Paul W. R. Harris
- School of Chemical Sciences, The University of Auckland
- School of Biological Sciences, The University of Auckland
- Maurice Wilkins Centre for Molecular Biodiscovery, The University of Auckland
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Cameron AJ, Squire CJ, Gérenton A, Stubbing LA, Harris PWR, Brimble MA. Investigations of the key macrolactamisation step in the synthesis of cyclic tetrapeptide pseudoxylallemycin A. Org Biomol Chem 2020; 17:3902-3913. [PMID: 30941386 DOI: 10.1039/c9ob00227h] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The total synthesis and structural confirmation of naturally occurring all l-cyclic tetrapeptide pseudoxylallemycin A is reported. X-ray crystallography revealed that the linear precursor adopted an all-trans (ttt) extended linear conformation, while its cyclic derivative adopts a trans,cis,trans,cis (tctc) conformation. Two kinetically favoured cyclic conformers prone to hydrolysis initially formed rapidly during cyclisation, with subsequent conversion to the thermodynamically stable tctc macrocycle taking place slowly. We postulate the initial unstable cyclic product undergoes an unprecedented nucleophilic ring opening with either the T3P or PyAOP by-products to give the linear ttt structure as a reactivated species and through a series of equilibria is slowly consumed by cyclisation to the thermodynamic product pseudoxylallemycin A. Consumption of the reactivated species by formation of pseudoxylallemycin A requires a trans-cis isomerism to occur and necessitates moderately increased reaction temperatures. Cyclisation with T3P was found to provide the greatest stereoretention. Synthesis and X-ray crystallography of the C-terminal epimer demonstrated its cyclisation to be kinetically favoured and to proceed without epimerisation despite also bearing an all-trans backbone.
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Affiliation(s)
- Alan J Cameron
- School of Chemical Sciences, The University of Auckland, 23 Symonds St, Auckland 1010, New Zealand.
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Davison EK, Cameron AJ, Harris PWR, Brimble MA. Synthesis of endolides A and B: naturally occurring N-methylated cyclic tetrapeptides. MEDCHEMCOMM 2019; 10:693-698. [PMID: 31191859 DOI: 10.1039/c9md00050j] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2019] [Accepted: 03/01/2019] [Indexed: 01/16/2023]
Abstract
Endolides A and B are naturally occurring, N-methylated, cyclic tetrapeptides possessing an unusual 3-(3-furyl)alanine amino acid and outstanding biological profiles. 1-Propanephosphonic anhydride (T3P) was used to mediate a solution-phase cyclisation reaction of the linear tetrapeptides, thus achieving the first syntheses of both endolides A and B. The stereoselectivity of the tetrapeptide cyclisation reactions was found to be reagent-controlled, and was independent of the C-terminal configuration of the linear peptide starting materials.
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Affiliation(s)
- Emma K Davison
- School of Chemical Sciences , University of Auckland , 23 Symonds St. , Auckland , 1010 , New Zealand . .,School of Biological Sciences , University of Auckland , 3 Symonds St. , Auckland , 1010 , New Zealand
| | - Alan J Cameron
- School of Chemical Sciences , University of Auckland , 23 Symonds St. , Auckland , 1010 , New Zealand . .,School of Biological Sciences , University of Auckland , 3 Symonds St. , Auckland , 1010 , New Zealand.,The Maurice Wilkins Centre for Molecular Biodiscovery , The University of Auckland , Private Bag 92019 , Auckland , 1010 , New Zealand
| | - Paul W R Harris
- School of Chemical Sciences , University of Auckland , 23 Symonds St. , Auckland , 1010 , New Zealand . .,School of Biological Sciences , University of Auckland , 3 Symonds St. , Auckland , 1010 , New Zealand.,The Maurice Wilkins Centre for Molecular Biodiscovery , The University of Auckland , Private Bag 92019 , Auckland , 1010 , New Zealand
| | - Margaret A Brimble
- School of Chemical Sciences , University of Auckland , 23 Symonds St. , Auckland , 1010 , New Zealand . .,School of Biological Sciences , University of Auckland , 3 Symonds St. , Auckland , 1010 , New Zealand.,The Maurice Wilkins Centre for Molecular Biodiscovery , The University of Auckland , Private Bag 92019 , Auckland , 1010 , New Zealand
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