The Diels-Alder reaction of cis-5,6-diacetoxy-l,3-cyclohexadiene (l), which has a rneso configuration, with the chiral nitroso dienophile 2 occurs with induction of four asymmetric centers in very high optical yield (ee = 94%) and leads to the dihydro oxazine 3 (89%). The influence of the reaction temperature on the asymmetric induction was investigated and the absolute configuration of the product determined. Reductive cleavage of the N -0 bond of 3 presents a simple route to enantiomerically pure derivatives of (1R)-conduramine A1 (82%).Aminocyclitols are essential structure elements of many biologically active compounds. They have been found in aminoglycoside-aminocyclitol (AGAC) antibiotics'), in Amaryllidaceae alkaloids ' ' , and as ligands of cytostatic platinum complexes3'. In connection with our work on the mutasynthesis of new AGAC4' we are interested in the enantioand stereoselective synthesis of aminocyclitols. The key step in our synthetic pathway is the hetero Diels-Alder reaction of activated nitroso compounds with substituted cyclohexadienes ' I. Diacetoxydiene 1 was obtained by acetylation of cis-5,6-dihydroxy-l,3-cyclohexadiene with acetic anhydride and pyridine in nearly quantitative yield. This dihydroxy diene was prepared by Nakajima from tetrachlorodihydroxycyclohexane6); it is also available by microbial dioxygenase oxidation of benzene'). A biotechnological process using mutants of Pseudomonas putida was recently developed and allows the synthesis of the dihydroxydiene in multikilogram amounts *). HN: HCI)(' ova NO CHCLJEtOH &OAc a :The Diels-Alder reaction of 1 with the protected l-chloro-1-nitrosomannose') 2 yields the dihydro oxazine 3. The stereochemistry of 3 was determined from the 'H-NMR spectrum. The chemical shifts of the acetyl proton signals at 6 = 2.01 and 2.03 prove the endo position of the acetoxy groups. Signals of acetyl groups in exo positions, which are not shielded by the anisotropic effect of the double bond, would be expected at 6 = 2.15"). The chemical shifts of the 7-H (6 = 5.38) and 8-H (6 = 5.50) signals are characteristic for exo protons and confirm this assignment.For the investigation of the stereo-and enantioselectivity, we carried out a number of Diels-Alder reactions at different temperatures and isolated product 3 without recrystallization. After disappearance of the blue color of the nitroso compound, the reaction mixtures were extracted with water, and the product mixtures were lyophilized. The 'H-NMR spectra of the crude products showed that the reaction is stereoselective even at room temperature. The attack of the dienophile 2 obviously takes place only anti to the acetoxy substituents, from the sterically less shielded face of diene 1. The enantioselectivities of the Diels-Alder reactions were determined by establishing the enantiomeric purity of the dihydro oxazines using derivatization of the crude products with (S)-3,3,3-trifluoro-2-methoxy-2-phenylpropionyl chloride, separation of the diastereomeric amides by HPLC, and integration of the individual ...

A total of 16 idiotrophic mutants unable to produce the aminoglycoside antibiotic streptomycin (smi) were isolated from Streptomyces griseus N2‐3‐11. Cosynthesis of streptomycin, its formation from various precursors and analysis of accumulated intermediates allowed grouping of the mutants in 3 classes, blocked: (I) in the first transamination step of the streptidine pathway; (II) in later steps of the streptidine pathway; or (III) outside streptidine biosynthesis.

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Die Darstellung und Diels-Alder-Reaktionen der Titelverbindung 3 mit a-chlornitrosoverbindungen (4, 7) werden beschrieben. Bei Verwendung des Androstanderivats 7 erhalt man hochstereoselektiv das Addukt ( +)-5a, dessen optische Reinheit nach verschiedenen Verfahren vergleichend bestimmt wird. Polyhydroxyamino Compounds via Diene Synthesis with Nitroso Compounds, XI). - tuans-5,6-Dimethoxy-1,3-cyclohexadiene as Educt for the Synthesis of Optically Active Streptamine PrecursorsThe synthesis and Diels-Alder reactions of the title compound 3 with a-chloronitroso compounds (4, 7) are described. Reaction with the androstane derivative 7 leads highly stereoselectively to the adduct ( +)-5a. The enantiomeric excess of this product was determined using several methods, the advantages and disadvantages of which are described.Im Rahmen unserer Arbeiten iiber die Synthese von Streptamin-Analogen, die sowohl aufgrund ihrer biologischen Aktivitat2) als auch als potentielle Edukte bei M~tasynthesen~) von Aminoglycosid-Antibiotika Interesse beanspruchen, haben wir bisher im ersten Syntheseschritt 1,3-Cyclohexadien4), trans-5,6-Diacetoxy-1,3-cyclohexadien') sowie 5-Hydroxy-6-N-substituierte Derivate'' als Edukte bei der Diels-Alder-Reaktion mit cL-Chlornitrosoverbindungen eingesetzt. In dieser Mitteilung beschreiben wir die Verwendung des bisher unbekannten trans-5,6-Dimethoxy-1,3-cyclohexadiens (3) als Edukt bei der Diels-Alder-Reaktion. Im weiteren Verlauf unserer Synthesen werden successive Acyloxy-und Acylaminogruppen am Cyclohexanring eingefiihrt. 3 als Edukt besitzt den Vorteil, da13 eine selektive Abspaltung der verschiedenen OH-bzw. NH2-Schutzgruppen moglich ist6). Ferner war von Interesse, unter Verwendung von 3 Verfahren zur asymmetrischen Diels-Alder-Reaktion, die wir vor kurzem ausarbeiteten 'a8), an einem substituierten Cyclohexandien-Derivat zu erproben. Wir haben schliel3lich an diesem Beispiel verschiedene Verfahren zur Bestimmung der optischen Ausbeute verglichen.((3 VCH Verlagsgesellschaft mbH, D

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