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Polypeptides
Published in Stanislaw Penczek, H. R. Kricheldorf, A. Le Borgne, N. Spassky, T. Uryu, P. Klosinski, Models of Biopolymers by Ring-Opening Polymerization, 2018
The nomenclature of stereoisomerism in the field of polymer chemistry suffers from inconsistencies and misleading definitions.201 Therefore, a short discussion (following points 1 to 3) of the nomenclature used in this section seems to be useful: The nomenclature of enantiomeric and diastereomeric monomers or monomer unitsThe nomenclature of stereoisomers sequences, such as dyads, triads, tetrads, etc.The definition of basic terms, such as stereospecificity, stereoselectivity, etc.
Advances in Nanobiocatalysis Strategies for Lipase Immobilization and Stabilization
Published in Mahmood Aliofkhazraei, Advances in Nanostructured Composites, 2019
Patel Vrutika, Ashok Pandey, Christian Larroche, Datta Madamwar
Stereospecificity is defined as the ability of lipases to distinguish between sn-1 and sn-3 position on the triglyceride. Lipases may show insignificant stereoselectivity or be very stereoselective. The stereoselectivity of the same enzyme may vary according to the structure of the substrate (Sonnet 1988). Lipases from Pseudomonas sp. and P. aeruginosa exhibit sn-1 preference with trioctanoin as a substrate while C. antarctica lipase B shows sn-3 preference, with high stereospecificity. All other microbial lipases show medium or low sn-1(3) stereospecificity toward trioctanoin (lipases from Rhizopus oryzae, R. miehei and C. rugosa hydrolyze trioctanoin preferably at sn-1 with low stereoselectivity) (Rogalska et al. 1993).
Serendipitous discovery of a regioselective synthesis of novel benzoyloxy substituted phenyl/benzyl-sulfanyl/selenylbisesters, 3-benzoyloxy-3-(phenylsulfanyl)-β-lactams and their antimicrobial evaluation
Published in Journal of Sulfur Chemistry, 2023
Dipika Narula, Shamsher S. Bari, Gulab Singh, Rajni Sharma, Ankita Garg, Aman Bhalla
In conclusion, a series of novel benzoyloxy substituted sulfanyl/selenylbisesters and β-lactams have been synthesized by the benzoyloxylation of appropriate sulfanyl/selenyl-monoesters and trans-3-phenylsulfanyl-β-lactams. The regioselective syntheticbenzoyloxylation protocol opens new possibilities to access sufficiently stable benzoyloxy compounds. Antimicrobial evaluation studies performed on benzoyloxy/m-chlorobenzoyloxy substituted benzylselenyl-bisesters suggest these to have significant antibacterial and antifungal properties. Further, we have shown that a change of stereochemistry at the C3 and C4 positions of β-lactam ring can exert a major influence on antimicrobial activity of 3-benzoyloxy-3-phenylsulfanyl-β-lactams, wherein the trans- isomer was active against all tested strains and the cis- isomer was completely inactive. These findings demonstrate the positive effects of diversely substituted benzoyloxy compounds as promising candidates for biological applications. In addition, preliminary investigations that utilize diversified chiral organocatalysts for accomplishing asymmetric α-benzoyloxylations on our substrates have already been initiated in our laboratory to access the benzoyloxy derivatives with high stereospecificity/stereoselectivity (de/ee).
Multi-stimuli-responsive, liposome-crosslinked poly(ethylene glycol) hydrogels for drug delivery
Published in Journal of Biomaterials Science, Polymer Edition, 2020
Luisa L. Palmese, Ming Fan, Rebecca A. Scott, Huaping Tan, Kristi L. Kiick
In order to first generate an enzymatically degradable hydrogel that would allow for future incorporation of liposomes via chemical crosslinking, a PEG hydrogel containing an MMP-degradable peptide was synthesized via Michael-type addition. The Michael-type reaction exhibits traditional advantages of click chemistry such as stereospecificity, few byproducts, lack of catalyst, and gentle reaction conditions [57], and has thus been widely used in biomaterials synthesis. However, the fast reaction rate can cause limitations in handling time and in forming homogeneous hydrogels during preparation, thus making these chemistries and hydrogels less practical for applications requiring longer reaction times. Lutolf et al. [58] and Darling et al. [59] have successfully tuned the kinetics of the Michael-reaction process by using different amino acids to alter the pKa of thiol groups. Such modifications of the surrounding chemical environment led to decrease in the rate of reaction with decrease in pKa, and the converse. Based on these reports, we synthesized a peptide containing an MMP-cleavable sequence sandwiched by a thiol-containing cysteine next to glutamic acid (E), as a functional crosslinker (GECEE-GPQGIWGQ-EECEG) (Figure S2). The particular sequence resulted in a slightly acidic local environment that slowed the reaction rate, enabling the hydrogel to be prepared at physiological temperature and pH.