Untersuchungen zum Mechanismus der Biosynthese von Cladinose und Desosamin mit Hilfe von D-Glucose-[U-14C-4-T]

Abstract

The mechanism of the biosynthesis of L-cladinose (I) and D-desosamine (II) was investigated with the aid of D-glucose- [U-¹⁴C-4-T] (III). When III was added to cultures of S. erythreus the T/¹⁴C ratio in I and II (isolated from erythromycin) was 38 to 74 per cent lower than in III. This loss of tritium could occur by: 1. The formation of exchangeable hydrogen during the reaction; 2. an intramolecular isotope effect; 3. partial degradation of the glucose and resynthesis by reversal of glycolysis, in which case the tritium at C-4 would be lost. As was shown by degradation neither cladinose nor desosamine contained tritium at C-6. Therefore an intramolecular hydrogen transfer from C-4 to C-6 such as that postulated in the biosynthesis of 6-deoxysugars could not be demonstrated. In both cladinose and desosamine all the tritium is very probably located at C-4. Therefore if a nucleotide bound 4-keto-6-deoxyhexose occurs as an intermediate as in the biosynthesis of 6-deoxy- and 3,6-dideoxysugars the tritium which is removed from the 4-position in this step must be reintroduced in this position in a later step.