Labile γ-glutamaldehydic acid (1) was first converted to tryptophan via its phenylhydrazone; no racemization occurred during the reaction. The stability of 1 was shown to be remarkably enhanced in the presence of additives.
The mixed solvent of nitromethane and hexane exhibited high stereoselectivity with good yields in the synthesis of ubiquinone-10 by the coupling of 2,3-dimethoxy-5-methylhydroquinone and isodecaprenol in the presence of a catalytic amount of BF3·OEt2.
Acknowledgment. We thank the National Science Foundation for support of this investigation (Grant No. CHE-7901763) and for financial aid in the purchase of a Nicolet 360 MHz spectrometer (Grant No. CHE-7922072). Also, we thank Richard Voegeli for his assistance in making the electrochemical measurements.
The alpha,alpha-gem-difluorination of 2',4'-difluoro-alpha-(methylthio)acetophenone (1a) with N-fluoropyridinium salts gave 2',4',alpha,alpha-tetrafluoro-alpha-(methylthio)acetophenone (3a). This reaction was accelerated by the addition of zinc chloride, zinc bromide or anhydrous iron(III) chloride, and higher yields than the reaction without additives were obtained. The gem-difluorination reaction using FP-T300 in the presence of zinc bromide was applicable to other alpha-(alkylthio)acetophenone derivatives (1).
Proline auxotrophs, which were induced from an L-proline-produdng strain of Brevibacterium flavumby indirect suppression mutation, accumulated L-glutamic-y-semialdehyde (GSA) in the fermentative broth. The addition of sulfite salts to the culture medium, when bacteria were exponentially growing, improved the accumulation of GSAfrom 2.3 to a maximumof 13.2 mg/ml. The direct use of GSAin the fermentative broth for the chemical synthesis of L-tryptophan was studied. The yield of L-tryptophan was 48% on the basis of GSAin the reaction mixture. The indole-condensation reaction between L-glutamic-y-semialdehyde (GSA) and phenylhydrazine has been developed as a new method for synthesizing L-tryptophan.1} A major problem with this method lies in the preparation of the l form of GSA. Several chemical and enzymatic methods are available for the synthesis of GSA.2~5) However, they are rather time-consuming and expensive procedures. Iriuchijima and Tsuchihashi reported that enzymatically prepared and purified 7V-acetyl-Lglutamic-y-semialdehyde was converted chemically into 7V-acetyl-5-benzyloxy-L-tryptophan.6)
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