have uploaded two page document "a new synthesis of threonine" from vol 30 no 6 1957 bulletin of the chemical society of japan. 1180-foto_1.jpg + 1181-foto_2.jpg. paper describes formation of copper glycinate, protonation of copper glycinate and addition of acetaldehyde to form threonine in 64% yield.
(https://www.thevespiary.org/rhodium/Rhodium/hive/hiveboard/picproxie_docs/000506443-foto_1.jpg)(https://www.thevespiary.org/rhodium/Rhodium/hive/hiveboard/picproxie_docs/000506443-foto_2.jpg)