delsig toolbox
In my mind, "synthesizeNTF" function is in the "delsig" toolbox, not in the "SDtoolbox". To understand the "delsig" toolbox, you can read book "Understanding of Delta-Sigma Data Convertor". There are several matlab codes in chapter 8 which worked perfectly. I think this codes will help you to know how to use "synthesizeNTF" function.
besides "synthesizeNTF", there are some other useful functions in "delsig". Since I am newbie in ADC design, I could only say that the "delsig" toolbox help me a lot in defining the coefficient for each branch and integrators.