N2 locants on more amino acids: N2-methyltryptophan

[rogersayle]

This is an enhancement request to support N2-methyltryptophan, as currently supported by ChemDraw. As you know, for acyclic standard amino acids, N2 may be used to name the "amino" group; but for cyclic standard amino acids, the integer locants refer to ring positions, such that greek characters are used to denote the acyclic parts of the sidechain , leading to the amino group being named Nalpha. Alas, not everyone understands the rules, leading to names like N2-methyltryptophan, where (fortunately) the atom called N2 remains unambiguous.

I'll be the first two admit that 2-aminotyptophan has a real N2 locant following IUPAC rules, but for cases where OPSIN's locant look-up fails, falling back to what the author probably intended may be preferable to failing; as the saying goes "nobody makes money from a 404 page not found". I shall of course use the correct Nalpha, but there's no reason why OPSIN shouldn't be able to interpret names that ChemDraw can.

Thanks in advance. Roger

[dan2097]

I can only find one name on the internet that has this mistake: S-(+)-N2-Methyltryptophan methyl ester, this sounds far more amenable to a dictionary based solution.

OPSIN does not aim to interpret all names that ChemDraw interprets, and this arises partially from the fact that some of ChemDraw's nomenclature principles are a trade-off between recall and precision, given the existence of trivial names. OPSIN does not do:

• Any Rule That Can Be Extended Should Be

and tries to avoid:

• If It Looks Like It Ought To Be a Rule, It Is a Rule