The D forms of amino acids sold commercially are considered to be synthetic. However, D forms of amino acids are not always synthetic. There are several D forms that exist in nature. In addition, amino acids can be racemized by the body and go back and forth between the D form and the L form quite easily. However, only L forms can be incorporated into proteins. For the purposes of dietary supplements, the L forms are natural and the D forms are synthetic. DLPA and DL-methionine are actually racemic mixtures of both L and D forms.
But there is no such thing as D-Taurine or D-Glycine; in other words, no synthetic forms exist of these two aminos since each only comes as one isomer that doesn’t polarize and rotate light to the right. Nor are there really L forms of these, since they do not polarize and rotate light to the left, either. There are simply single, natural isomers of just plain Glycine and Taurine.
Don’t assume that all D or L forms of molecules are good or bad, since it really depends on the individual substance concerned. For example, the D isomers of vitamin E are the natural forms and the L isomers are synthetic; just the opposite of amino acids. Thus the terminology and forms of what is natural or synthetic will vary by substance. Some natural molecules exist as L form, some as D form and some have only one form, whether in food or if synthesized.
NOW® prides itself as being science-based. We only sell natural form amino acids and Vitamin E and we use the correct scientific names for substances and compounds on our labels.