He began teaching as an assistant, initially in the inorganic chemistry department, before becoming an associate professor in 1886.

In 1900, he devised a simpler method for obtaining pyrimidine using barbituric acid, and in 1903 he first prepared quinazoline.

[1] Gabriel was a member of the German Chemical Society and served on its board for many years.

Siegmund and Anna Gabriel had two sons: Ernst, born in 1885, became a dermatologist and later earned his living as a chicken farmer after his emigration to Israel;[3] Kurt, born in 1896, became a dentist and was able to continue to work in this profession after emigrating to New Zealand.

[5] Original documents from Siegmund Gabriel's estate have been kept at the Leo Baeck Institute in New York since 1979.