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Molds
Published in William J. Rea, Kalpana D. Patel, Reversibility of Chronic Disease and Hypersensitivity, Volume 5, 2017
William J. Rea, Kalpana D. Patel
According to Bohnert et al.166 small peptide toxins, the diketopiperazines, gliotoxin, and sirodesmin PL (Figure 1.2), and their biosynthesis loci have received particular attention. Gliotoxin is a metabolite of various fungi, with the opportunistic human pathogen A. fumigates being the most relevant producer. Sirodesmin PL is a phytotoxin of Leptosphaeria maculns, the causative agent of canola blackleg disease. Gliotoxin and sirodesmin share disulfur bridges as key structural prerequisite to generate reactive oxygen species and to conjugate with cysteine residues of proteins. Effects on prokaryotic or eukaryotic cells include, among numerous others, necrotic and apoptotic cell death, and NFkB activation.177 The key enzymes for gliotoxin and sirodesmin synthesis are the NRPSs GliP and SirP, respectively, which assemble the diketopiperazine core structure from l-serine and an aromatic l-amino acid. Disruption of sirP led to a mutant which lost the capacity to produce sirodesmin.
Microwaves in Lactam Chemistry
Published in Banik Bimal Krishna, Bandyopadhyay Debasish, Advances in Microwave Chemistry, 2018
Dr. Debasish Bandyopadhyay, Bimal Krishna Banik
A convenient strategy for the conversion of [2.2.2]-diazabicyclic alkene structures to 2-pyridone (δ-lactam) aromatic heterocyclic products has been reported [62] that involves the formation of an intermediate 2,5-diketopiperazine derivative (12). In the final step, a retro [4 + 2]-Diels–Alder cycloreversion and selective extrusion of cyanate derivatives under microwave (300W, 1h) irradiation produced 2-pyridone (13) in moderate yield (Scheme 10.6). This methodology was effectively implemented to synthesize novel anticancer alkaloid Louisianin A (14, Scheme 10.6).
Diastereomeric discrimination by achiral substances: the effect of diverse ions in the stability of amphi-ionophore cystine-based cyclopeptide stereoisomers
Published in Molecular Physics, 2019
Samaneh Ahmadi, Hossein A. Dabbagh, Saeid Ebrahimi, Hossein Farrokhpour
The studied cystine-based cyclopeptides are constructed from two cystine units (Scheme 1). The cystine with two chiral centres is disulfide form of two cysteine molecules. The binding of two cystine units occurs via four amid linkage constructs tricyclopeptide (TCP) structure. A tricyclopeptide (TCP) contains two 2,5-diketopiperazine (2,5-DKP) rings which are known as the smallest cyclic anhydrous dipeptide. The 2,5-DKPs has two configurations as cis and trans stereoisomers, where two nitrogen atoms and the two carbonyl groups are at opposite places.
Gelation of ionic liquids by small-molecule gelators and their applications
Published in Soft Materials, 2020
Wangkhem Paikhomba Singh, Utpal Koch, Rajkumar Sunil Singh
Hanabusa and coworkers have reported two cyclic dipeptides (2 & 3) prepared from L-asparaginyl-L-phenylalanine methyl ester (aspartame), capable of forming gels with an extensive array of ILs which included different imidazolium, pyridinium, ammonium, piperidinium, pyrazolidinium, and morpholinium salts bearing different anions.[42] Minimum gelation concentration (MGC) values observed for gelation of the different ILs ranged between 0.3% and 3.0% w/v. The IL-gels were highly thermally stable (up to 140°C), electrochemically stable, and possessed a wide electrochemical window. The ionic conductivities of the neat ILs and IL-gels were comparable which indicates that the confinement of the gelator molecules within a gel-network doesn’t interfere with the movement of ions. Such kind of observations has been made for many other IL-gelators as discussed subsequently in this review. The plausible explanation is that the typically low gelator concentration required for gelation produces low-density fibrous networks which do not hamper the free movement of ions and, hence, ionic conductivities of the IL-gels and ILs are comparable. Among the IL-gels, gels prepared with [C4mim][NTf2] & [C4mim][BF4] showed the highest conductivity (~3.4 × 10−3 S cm−1 at room temperature). Furthermore, the ionic conductivities could be increased by two-fold if IL-gels were prepared in the presence of propylene carbonate. From cyclic voltammetric studies, it was established that IL-gels prepared with 2 and [C4mim][BF4]/[Et2MeC3ON][NTf2] were electrochemically stable over a wide potential range. The authors attributed this observation to the presence of the highly stable six-member cyclic 2,5-diketopiperazine structure in 2.
Theoretical study of the mechanism of 2,5-diketopiperazine formation during pyrolysis of proline
Published in Molecular Physics, 2020
Cristian Cervantes, José R. Mora, Luis Rincón, Vladimir Rodríguez
Theoretical studies on the mechanisms of pyrolysis of proline at low temperature demonstrated, through comparison of enthalpies of activation, that formation of 2,5-diketopiperazine is more favoured than the unimolecular decomposition of this amino acid, which is in good agreement to experimental studies where this adduct have been identified as the major product while volatiles are practically absent [8]. The above mentioned agreement, along with the values found for normalised enthalpies of transition states and intermediates, supports the proposed mechanism. The transition state corresponding to the first dehydration process (TS2) was determined as the rate-controlling state of the profile, while the diol which precedes this elimination of water (INT1) is assumed as the rate-influential intermediate due to its apparent stability. The activation energy needed to achieve whether TS1 (reverse direction) or TS2 (forward direction) from INT1 is predominantly used in geometrical rearrangements, which is evidenced in the values of the corresponding integrated reaction force works and the analysis of the changes in bond lengths and bond angles in Figure 3. Here, the geometrical rearrangements needed to achieve TS2 are dominated by the approximation of the oxygen atoms involved in the proton transfer, while electronic rearrangements depend on the almost formation of the molecule of water just before its separation from the molecular matrix. Electronic rearrangements do not need a significant charge transfer as can be noticed in Table 3 due to the low values obtained for differences of charge (). The latter is possibly because rupture and formation of bonds during the dehydration occur almost at the same time with only a slight asynchronicity, as can be evidenced by Wiberg bond indexes and Synchronicity value in Table 4. All this data provides new detailed insights on the low-temperature pyrolysis of proline, which is considered a target amino acid when formation of 2,5-diketopiperazine products is studied.