Biosynthesis of tetrocarcin. Incorporation of 14C- and 13C-labeled compounds into tetrocarcin.

Micromonospora chalcea KY11091 produces tetrocarcin, showing antibacterial activity against Gram-positive bacteria and antitumor activity against experimental murine tumors.'-'> Tetrocarcin A, a major component, consists of a thirteen-membered macrocyclic ring containing tetronic acid (tetronolide),°> a nitro sugar (tetronitrose, the same as kijanose')) and deoxy sugars. The antibiotics known to have a similar aglycone to tetronolide are chlorothricin~> and kijanimicin9>. But they are different from tetrocarcin in several points. The unusual structural features of tetrocarcin prompted us to initiate a study of its biosynthesis. In this report, the incorporation of "Cand 13C-labeled compounds into tetrocarcin is described. Compounds labeled with '4C were added at a concentration of 0.25 pCi/ml to a producing culture of M. chalcea KY11091 in a chemically defined medium') two days after inoculation. Labeled tetrocarcin A was extracted with ethyl acetate at pH 2 from the culture filtrate and purified by preparative TLC (Silica gel 60 F2S4, Merck, CHCl3 MeOH, 9: 1 v/v). Compounds labeled with 13C were added at a concentration of 0.05°o to a producing medium consisting of 2 % soluble starch, 0.1 % yeast extract, 0.05% soy bean meal, 1 % peptone A, 0.05 % K2HPO4i 0.05 % MgSO4.7H2O and 0.1 % CaCO3 two days after inoculation. The culture filtrate was extracted with ethyl acetate at pH 2, followed by hydrolysis with 0.2 N HCI acetone at 80°C for 2 hours to give tetronitrosyl tetronolide. Tetronitrosyl tetronolide labeled with '3C was purified by preparative TLC (Silica gel Table 1. Incorporation of 14C-labeled compounds into tetrocarcin A.