I managed to convert the syn file of the latin english inflected, using the penelope tool developed by alberto pettarin (who deserves a lot of praise for his work!). I am posting it here, it should work on Koreader, I have tried it on my tablet with zo reader (which also doesn't recognize the syn files) and it works.
This work is assumed to be in the Life+70 public domain OR the copyright holder has given specific permission for distribution. Copyright laws differ throughout the world, and it may still be under copyright in some countries. Before downloading, please check your country's copyright laws.
If the book is under copyright in your country, do not download or redistribute this work.
To report a copyright violation you can
contact us here.