Michael Schön

Single Operation Stereoselective Synthesis of Aerangis Lactones: Combining Continuous Flow Hydrogenation and Biocatalysts in a Chemoenzymatic Sequence

Over the last two decades, biocatalysis has matured into a generally accepted approach for laboratory-scale reactions and industrial processes. Selectivity and environmental sustainability of enzymatic transformations are often superior relative to their chemical counterparts, and these transformations ultimately offer the prospect of reducing production costs by minimizing waste and maximizing product output. This competition, however, can never designate a single champion. In many cases, chemical catalysts, especially when paired with a continuous flow reactor design, are difficult to beat in terms of volumetric productivity with state of the art technology. For a long time, laboratory chemistry was confined to the domain of batch reactors. With the emergence of continuous flow reactor devices for research, the field was open for the development of reactions that can rather easily be scaled up to higher volumes without the need for extensive engineering. Within this study, it was our particular aim to combine the two worlds of heterogeneous catalysis and biocatalysis into one simple process that features the excellent selectivity of enzymes and the high productivity of heterogeneous catalytic entities in continuous flow. We identified the aroma compound Aerangis lactone [(S,S)-3] as a suitable target for our proof-of-concept case study: Its two chiral centers allow the selectivity of an integrated chemoenzymatic process to be demonstrated, and its synthetic accessibility from a cheap starting material enables the simplicity of our approach to be outlined (Scheme 1). The target compound possesses highly interesting olfactory properties: it was characterized as the main odor component of African white-flowering orchids and is widely used in the perfume and cosmetics industries. The immediate advantages of our concept involving the integration of chemoenzymatic processes can easily be reasoned by comparison to previous routes towards the asymmetric product. Various multistep stereoselective syntheses consisting of a minimum of seven steps have been reported for (S,S)-3, but their complexity and elaborate protecting group chemistry prohibits efficient production of (S,S)-3 on a larger scale. A simple but completely unselective two-step approach to Aerangis lactone was described in a patent by Kaiser starting from cheap dihydrojasmone (1; <150 E kg , Sigma–Aldrich) through catalytic hydrogenation to saturated ketone 2 and subsequent Baeyer–Villiger oxidation (BVOx); however, this route yielded a mixture of all four possible stereoisomers of 3. We based our process design on this principal approach by additionally employing diastereoand enantioselective catalysts to specifically produce natural (5S,6S)-3 in a single operation by hydrogenation in continuous flow and enzymatic BVOx in a subsequent batch reactor. This approach should overcome safety issues by limiting the amount of pressurized reaction volume during the hydrogenation phase. Furthermore, hazardous reagents (such as peracids) can be replaced by alternatively utilizing Baeyer–Villiger monooxygenases (BVMOs), which operate with molecular oxygen as a primary oxidant at ambient pressure. Finally, application of a flow chemical setting also enabled single-operation access to epimer (5R,6S)-3. The design of the envisioned single-operation procedure demanded that certain prerequisites be met for the single reaction steps and further required additional adaptations to facilitate the direct coupling of the reactors in-line without interScheme 1. Stereoselective synthesis of natural Aerangis lactone [(S,S)-3] and its epimer (R,S)-3 via nonisolated saturated ketones 2. Reagents and conditions: a) 5 % Rh/C, Cs2CO3 1:5; H2; 0.5 m 1 in heptane; 30 8C; 1.0 mL min 1 c.f. ; quant. b) Amberlyst 15, 0.5 m cis-2 in heptane, 25 8C, 1.0 mL min 1 c.f. , quant. c) Up to 20 mm cis-2, G6P (0.5 equiv.), 2 % w/v CDMO crude cell extract, 5 U ml 1 G6PDH, 2 % w/v Triton X-100, 200 mm NADP , 50 mm TrisHCl pH 7.1, water. d) Same conditions as those given in c) by using CPMO instead of CDMO. c.f. = continuous flow, CDMO = cyclododecanone monooxygenase, CPMO = cyclopentanone monooxygenase, G6PDH = glucose-6-phosphate dehydrogenase, G6P = glucose-6-phosphate.

Application of continuous flow and alternative energy devices for 5-hydroxymethylfurfural production.

Dehydration of fructose and glucose in dipolar, aprotic solvents leads to formation of 5-hydroxymethylfurfural. Conditions for continuous flow reactions using a cartridge-based reactor system and a stop-flow microwave reactor were established showing very good product yields and selectivity without the limitation of a batch process such as upscaling and precise temperature monitoring and control. A maximum product HPLC yield of 90.3% under cartridge-based heating and 85.6% under microwave heating could be achieved using mild and quick reaction conditions. Formation of levulinic acid as a by-product could not be detected under the optimized reaction conditions.

VUT-MK142 : a new cardiomyogenic small molecule promoting the differentiation of pre-cardiac mesoderm into cardiomyocytes

Intra-cardiac cell transplantation is a new therapy after myocardial infarction. Its success, however, is impeded by the limited capacity of donor cells to differentiate into functional cardiomyocytes in the heart. A strategy to overcome this problem is the induction of cardiomyogenic function in cells prior to transplantation. Among other approaches, recently, synthetic small molecules were identified, which promote differentiation of stem cells of various origins into cardiac-like cells or cardiomyocytes. The aim of this study was to develop and characterise new promising cardiomyogenic synthetic low-molecular weight compounds. Therefore, the structure of the known cardiomyogenic molecule cardiogenol C was selectively modified, and the effects of the resulting compounds were tested on various cell types. From this study, VUT-MK142 was identified as the most promising candidate with respect to cardiomyogenic activity. Treatment using this novel agent induced the strongest up-regulation of expression of the cardiac marker ANF in both P19 embryonic carcinoma cells and C2C12 skeletal myoblasts. The activity of VUT-MK142 on this marker superseded CgC; moreover, the novel compound significantly up-regulated the expression of other cardiac markers, and promoted the development of beating cardiomyocytes from cardiovascular progenitor cells. We conclude that VUT-MK142 is a potent new cardiomyogenic synthetic agent promoting the differentiation of pre-cardiac mesoderm into cardiomyocytes, which may be useful to differentiate stem cells into cardiomyocytes for cardiac repair. Additionally, an efficient synthesis of VUT-MK142 is reported taking advantage of continuous flow techniques superior to classical batch reactions both in yield and reaction time.

Library synthesis of cardiomyogenesis inducing compounds using an efficient two-step-one-flow process

Within this work we telescoped a batch laboratory scale synthesis towards a two-step-one-flow process to synthesize cardiomyogenesis inducing compounds (4,6-diaminopyrimidines) in continuous manner. Special attention was put on a quick and robust screening protocol and subsequent UHPLC analysis. Finally, the robustness of the method was proven by the multi-gram synthesis of VUT-MK142 using a laboratory scale continuous flow reactor, enabling to deliver enough material for extensive biological testing.Graphical abstract