Citation: Venturi, V.; Lerin, L.A.; Presini, F.; Giovannini, P.P.; Catani, M.; Buratti, A.; Marchetti, N.; Dilliraj, L.N.; Aprile, S. Enzymatic Synthesis of Ascorbic Acid-Ketone Body Hybrids. Catalysts 2023, 13, 691. https://doi.org/10.3390/ catal13040691 Academic Editors: Yan Zhang and Raushan Kumar Singh Received: 16 March 2023 Revised: 28 March 2023 Accepted: 31 March 2023 Published: 1 April 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). catalysts Article Enzymatic Synthesis of Ascorbic Acid-Ketone Body Hybrids Valentina Venturi 1 , Lindomar Alberto Lerin 2 , Francesco Presini 2 , Pier Paolo Giovannini 2, * , Martina Catani 2 , Alessandro Buratti 2 , Nicola Marchetti 2 , Latha Nagamani Dilliraj 2 and Simona Aprile 2 1 Department of Environmental and Prevention Sciences, University of Ferrara, Via Luigi Borsari, 46, 44121 Ferrara, Italy; valentina.venturi@unife.it 2 Department of Chemistry, Pharmaceutical and Agricultural Sciences, University of Ferrara, Via Luigi Borsari, 46, 44121 Ferrara, Italy; lindomaralberto.lerin@unife.it (L.A.L.); francesco.presini@unife.it (F.P.); martina.catani@unife.it (M.C.); alessandro.buratti@unife.it (A.B.); nicola.marchetti@unife.it (N.M.); latha7481@yahoo.com (L.N.D.); simona.aprile@unife.it (S.A.) * Correspondence: pierpaolo.giovannini@unife.it; Tel.: +39-053-297-4532 Abstract: Molecular hybrids obtained by connecting two or more bioactive molecules through a metabolizable linker are used as multi-target drugs for the therapy of multifactorial diseases. Ascorbic acid, as well as the ketone bodies acetoacetate and (R)-3-hydroxybutyrate, are bioactive molecules that have common fields of application in the treatment and prevention of neurodegenerative diseases and cardiac injuries as well. In spite of this, the preparation of ascorbic acid ketone body hybrids is uncovered by the literature. Herein, we report the lipase-catalyzed condensation of methyl acetoacetate with ascorbic acid, which affords the 6-O-acetoacetyl ascorbic acid in quantitative yield. The same approach, employing the methyl (R)-3-hydroxybutyrate in place of the methyl acetoacetate, allows the preparation of the 6-O-(R)-3-hydroxybutyryl ascorbic acid in 57% yield. A better result (90% overall yield) is achieved through the lipase-catalyzed coupling of ascorbic acid with methyl (R)-3-O-methoxymethyl-3-hydroxybutyrate followed by the cleavage of the MOM protecting group. The two novel products are fully characterized and additional information on the antioxidant activity of the new products is also given. Keywords: molecular hybrids; ascorbyl esters; lipase; biocatalysis; antioxidant activity 1. Introduction Humans have exploited for millennia the properties of plant-derived foods and bever- ages to preserve their health, and the knowledge growth in various scientific fields has led to the identification of the substances responsible for the protective or curative effects. More recently, thanks to in vitro as well as in vivo experiments, the mechanisms by which many plant-derived bioactive compounds produce health benefits have been discovered [1,2]. It is worth noting that a number of bioactive compounds are employed in the treatment or prevention of multifactorial diseases, namely illnesses with complex etiopathology due to the involvement of multiple organ systems and tissues [3]. The treatment of such dis- eases moved from the traditional single-drug therapy toward multidrug approaches that include the administration of drug cocktails or multicomponent drugs obtained by the co-formulation of more than one active ingredient [4]. An alternative emerging strategy is the design of multi-target drugs that integrate multiple pharmacophores into a single drug molecule in order to simultaneously act at multiple sites of relevance to a disease [5,6]. Multi-target drugs can be prepared by connecting two or more drugs through a stable or metabolizable linker or by merging the haptophoric moieties of different drugs. The two strategies afford hybrid and chimeric drugs, respectively [3], although this specification is not strictly followed in the literature and the term molecular hybrid is often used to indi- cate multi-target drugs achieved through both connection strategies [3,7]. Many bioactive natural products have been employed as a starting scaffold in multi-target drug discovery Catalysts 2023, 13, 691. https://doi.org/10.3390/catal13040691 https://www.mdpi.com/journal/catalysts