Frank Berto, in ‘The Dancing Chain’ mentions ‘Tectoran’ as a minor German derailleur brand in the early 1950’s - although I have personally never seen any relevant derailleurs from this period..

The ‘Tectoron’ derailleurs shown here were made by VEB Polygraph Druckmaschinenwerke Leipzig, a company that specialized in manufacturing printing machines (and that kind-of still exists under the Zirkon name).

Tectoron derailleurs appear to have been supplied to Diamant (the largest quality bicycle manufacturer in the DDR - now part of Trek) from about 1978 onwards, perhaps replacing Renak pull-chain derailleurs at that (relatively late) date. The black example below has a date on its guarantee card of 1990, indicating that the brand survived the fall of the Berlin Wall.