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Laccase-Mediated Synthesis of Novel Antibiotics and Amino Acid Derivatives
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2019
One the one hand, these dimers can be linked by one bond between the monomers forming C–O linked (defined as type I dimers), C–C linked (defined as type IIa and type IIb dimers) or S–S linked products (defined as type III dimers) (Fig. 8.2, left part, Table 8.1a). On the other hand, dimers linked by two bonds can be created, and these may also involve C–O, C–N and/or C–S bond formation (defined as type IV dimers). These reactions are referred to as “oxidative coupling,” “oxidative condensation” or “phenolic oxidative coupling” respectively. After longer reaction times oligomers and polymers can be generated from the dimers type I and IIa. Apart from these homomolecular coupling reactions laccases are also able to couple a laccase substrate (aromatics with hydroxyl, amino or mercapto group or groups) and a non-laccase substrate (variable reaction partner) to create new heteromolecular hybrid molecules (Fig. 8.2, right; Table 8.1b). This sort of reaction can result in (i) phenolic structures (type V dimers), (ii) quinoid structures (type VI dimers), (iii) quinonimin structures (type VII dimers), (iv) phenazines, phenoxazinones, benzothiadiazinones (type VIII dimers), (v) cycloheptenes (type IX dimers), (vi) cyclooctenes (type X dimers), and (vii) diazaspiro cyclohexenes (type XI dimers) and further work may well turn up other possibilities.
Orders Norzivirales and Timlovirales
Published in Paul Pumpens, Peter Pushko, Philippe Le Mercier, Virus-Like Particles, 2022
Paul Pumpens, Peter Pushko, Philippe Le Mercier
The next functionalization approach was achieved by the Francis team by oxidative coupling to aniline-containing side chains (Carrico et al. 2008; Stephanopoulos et al. 2009; Tong et al. 2009). Thus, the one-to-one oxidative coupling of aniline with N,N-diethyl-N’-acylphenylene diamine using sodium periodate was achieved for the attachment of peptides to the surface of the MS2 VLPs (Carrico et al. 2008). The aniline functionality was installed into the MS2 capsid through the incorporation of an unnatural amino acid residue, namely para-amino-L-phenylalanine (pAF), by amber suppression methods. To optimize the surface-accessible pAF incorporation, the five stop codon variants were constructed: Q6TAG, D11TAG, T15TAG, D17TAG, and T19TAG, and the appropriate suppression technique was applied, where the observable MS2 coat protein expression was found only in the presence of pAF. As the MS2 mutant with pAF at position T19 produced the highest yield and was found to be the robust oxidative coupling scaffold, it was used for all subsequent experiments. Three peptides known to target specific tissues were attached by the oxidative coupling via N,N-diethyl-N’-acylphenylene diamine, which was placed at the N-terminus of each peptide during synthesis on the solid phase. The oxidative coupling to aniline was also used to decorate the exterior surface of the MS2 particles with zinc porphyrins for photocatalysis (Stephanopoulos et al. 2009) and a DNA aptamer for cellular delivery (Tong et al. 2009). Furthermore, a highly efficient protein bioconjugation method involving addition of anilines to o-aminophenols in the presence of sodium periodate was used (Behrens et al. 2011). The impressive progress in the dual-surface modification of MS2 capsids and generation of novel nanomaterials was summarized at that time by Witus and Francis (2011). The detailed protocol on how to conjugate antibodies to the MS2T19pAF VLPs was published by ElSohly et al. (2018).
Chimeric VLPs
Published in Paul Pumpens, Single-Stranded RNA Phages, 2020
The next functionalization approach was achieved by Francis’ team by oxidative coupling to aniline-containing side chains (Carrico et al. 2008; Stephanopoulos et al. 2009; Tong et al. 2009). Thus, the one-to-one oxidative coupling of aniline with N,N-diethyl-N’-acylphenylene diamine using sodium periodate was achieved for the attachment of peptides to the surface of the MS2 VLPs (Carrico et al. 2008). The aniline functionality was installed into the MS2 capsid through the incorporation of an unnatural amino acid residue, namely, para-amino-L-phenylalanine (pAF) by amber suppression methods. To optimize the surface accessible pAF incorporation, the five stop codon variants were constructed: Q6TAG, D11TAG, T15TAG, D17TAG, and T19TAG, and the appropriate suppression technique was applied, where the observable MS2 coat protein expression was found only in the presence of pAF. As the MS2 mutant with pAF at position T19 produced the highest yield and was found to be the robust oxidative coupling scaffold, it was used for all subsequent experiments. Three peptides known to target specific tissues were attached by the oxidative coupling via N,N-diethyl-N’-acylphenylene diamine, which was placed at the N-terminus of each peptide during synthesis on the solid phase. The oxidative coupling to aniline was also used to decorate the exterior surface of the MS2 particles with zinc porphyrins for photocatalysis (Stephanopoulos et al. 2009) and a DNA aptamer for cellular delivery (Tong et al. 2009). Furthermore, a highly efficient protein bioconjugation method involving addition of anilines to o-aminophenols in the presence of sodium periodate was used (Behrens et al. 2011). The impressive progress in the dual-surface modification of MS2 capsids and generation of novel nanomaterials was summarized at that time by Witus and Francis (2011). The detailed protocol on how to conjugate antibodies to the MS2T19pAF VLPs was published recently by ElSohly et al. (2018). The practical results of the pioneering studies of Francis’ team are presented in the summarizing Table 23.1 of Chapter 23, together with other achievements by the addressing/targeting/delivery applications of the RNA phage VLPs.
Covalent drug discovery using sulfur(VI) fluoride exchange warheads
Published in Expert Opinion on Drug Discovery, 2023
Besides the common approaches mentioned above, alternative methods to introduce sulfonyl fluorides using diverse substrates and conditions have been developed. Among them, aryl halides [68,69], sulfonamides [70], and arenediazonium salts [71] are all useful precursors to generate sulfonyl fluorides in good to excellent yields (Figure 4a, formula 7–9). The Noël group reported an electrochemical oxidative coupling of thiols with KF to furnish sulfonyl fluorides (Figure 4a, formula 10) [72]. The substrate scope covered aryl, heteroaryl and alkyl thiols/disulfides. Further, a continuous-flow protocol was developed for this approach recently which enabled scale-up in a short reaction time (5 minutes) [73].
Iodine-mediated one-pot intramolecular decarboxylation domino reaction for accessing functionalised 2-(1,3,4-oxadiazol-2-yl)anilines with carbonic anhydrase inhibitory action
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2018
Srinivas Angapelly, P. V. Sri Ramya, Rohini Sodhi, Andrea Angeli, Krishnan Rangan, Narayana Nagesh, Claudiu T. Supuran, Mohammed Arifuddin
Construction of O–heterocyclic ring systems via intramolecular C–O bond formation has become an emerging tool in drug discovery. Accordingly, many efforts have been devoted to this activity, and remarkable results have been achieved to date. Among these, the traditional intramolecular Pd-catalysed Hartwig–Buchwald1 and copper-catalysed2 Ullmann-type C–O coupling of aryl halides with hydroxyl moieties, and in an alternative approach, the direct dehydrogenative coupling occurs between C–H and O–H bonds3, leading to various functionalised compounds. In most cases, these elaborative designs implied complex catalytic systems (based on Pd(II), Cu(II), Rh(III), and Ru(III) derivatives) and multi-step processes for the preparation of diversely functionalised derivatives, such as, furan, pyrrole, pyrazole, isoquinoline, indole, benzoxazole, and carbazole ring systems4. However, oxidative decarboxylation leading to construction of C–heteroatom bonds, particularly the C–O and the C–N bonds, has received significantly less attention. In recent years, in the perspective of green chemistry, most of the organic chemists have switched to metal-free reactions to reduce the burden of toxicity. In this context, iodine and hypervalent iodine reagents have emerged as inexpensive, versatile, and environmentally more friendly reagents5. Structural features and the reactivity pattern of these iodine compounds in many aspects are similar to those of the transition metal compounds applied for such purposes. Up until now, many efforts have been made to directly functionalise C–H bonds for the construction of C–C and C–heteroatoms bonds by employing iodine or hypervalent iodine reagents6,7. Wang et al. demonstrated a facile access to various heterocycles (quinazoline, oxazole, and pyridine) through the tandem oxidative coupling reactions using iodine as catalyst and tert-butyl-hydroperoxide (TBHP) as the oxidant8. Furthermore, Ma et al. proposed the synthesis of imidazo[1,2-a]pyridines via oxidative coupling of 2-aminopyridine with 1,3-diketones in the presence of tetra-butylammonium iodide (TBAI), TBHP, and BF3·etherate9. Very recently Tang et al. reported iodine-catalysed radical oxidative annulation for the synthesis of dihydrofurans and indolisines10. Interestingly, I2 (or hypervalent iodine derivatives) also promoted the oxidative decarboxylation of amino acids and β,γ-unsaturated carboxylic acids11. Intrigued by these advances, herein we envisioned a metal-free, iodine-mediated domino strategy involving intramolecular decarboxylative coupling of isatins, and hydrazides for the synthesis of 2-(1,3,4-oxadiazol-2-yl)aniline derivatives (Scheme 1).