Chemoenzymatic syntheses of (-)-1-deoxymannojirimycin (DMJ) and its naturally occurring 6-O-alpha-L-rhamnopyranosyl glycoside

Benzoate dioxygenase fromRalstonia eutrophaB9 – unusual regiochemistry of dihydroxylation permits rapid access to novel chirons

Oxidation of benzoic acid by a microorganism expressing benzoate dioxygenase leads to the formation of an unusualipso,orthoarenecis-diol in sufficient quantities to be useful for synthesis.

The role of biocatalysis in the asymmetric synthesis of alkaloids

Alkaloids are not only one of the most intensively studied classes of natural products, their wide spectrum of pharmacological activities also makes them indispensable drug ingredients in both traditional and modern medicine. Among the methods for their production, biotechnological approaches are gaining importance, and biocatalysis has emerged as an essential tool in this context. A number of chemo-enzymatic strategies for alkaloid synthesis have been developed over the years, in which the biotransformations nowadays take an increasingly 'central' role. This review summarises different applications of biocatalysis in the asymmetric synthesis of alkaloids and discusses how recent developments and novel enzymes render innovative and efficient chemo-enzymatic production routes possible.

Diversity-oriented synthesis of enantiomerically pure steroidal tetracycles employing Stille/Diels-Alder reaction sequences

Various steroid analogues were synthesized by Stille coupling of bicyclo[4.3.0]nonenylstannanes cis-/trans-8 and 14 with cyclohexenol triflates 17 and 18 and subsequent Diels-Alder reactions of the resulting dienes. The enantiomerically pure bicyclo[4.3.0]nonenylstannanes cis- and trans-8 were prepared in good yields via the enol triflates cis- and trans-7, obtained from the bicyclo[4.3.0]non-2-en-3-one 5. The alkenylstannane 14 was obtained from the [2+2] cycloadduct 10 a produced from addition of dichloroketene to the enantiomerically pure and protected bishydroxycyclohexadiene 9 a (65 %). Treatment of 10 a with diazomethane, reduction of the dichloromethylene group, and trapping with tributyltin chloride after lithium-for-bromine exchange, yielded the bicyclo[4.3.0]nonenylstannane 14 (23 % over four steps). Stille couplings provided the tricyclic dienes cis-/trans-19 in good yields (73-77 %), whereas the tricyclic diene 20 was obtained in only 34 % yield at best. Diels-Alder reactions of trans-19 with various reactive dienophiles yielded the novel steroidal compounds trans-21 to trans-26 with complete diastereoselectivity. Heating the dienes cis-19 or 20 with maleic acid derivatives provided the corresponding tetracycles cis-23alpha,beta and 27alpha,beta with a cis-C,D ring junction, each as mixtures of two diastereomers. Less reactive dienophiles required higher temperatures to promote the relevant cycloaddition with trans-19 to furnish several stereoisomeric forms of trans-28 and trans-29 in significantly lower yields (31-45 %). The selected steroid analogues trans-22 and trans-23 were deprotected in two steps by using acid catalysis to provide trans-31 and trans-33 (91 and 80 % over two steps). Cyclopropanation of trans-30 yielded the cyclopropasteroid analogue 34 (74 %), treatment of which with trifluoroacetic acid furnished the cyclopropasteroid 35 and the 2-methyl-substituted steroid analogue 36 in 40 and 12 % yield, respectively. Aromatic B-ring steroids 38 (69 %) and 39 (5 %) were accessed by dehydrogenation of trans-24 with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone.

Synthesis of 4-O-glycosylated 1-deoxynojirimycin derivatives as disaccharide mimics-based inhibitors of human β-glucocerebrosidase

Examples of a new type of inhibitor of human beta-glucocerebrosidase based on imino-disaccharides as glycosylceramide mimetics have been synthesized by way of the glycosylation of 1-deoxynojirimycin derivatives with 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl bromide.