Glucosamine

[JonasSchaub]

Me again, asking about sugars (sorry):

OPSIN usually returns the open-chain form for sugars unless explicitly specified otherwise (Glucose -> open-chain form; Glucopyranose -> ring form), which is correct according to the IUPAC nomenclature.

But for "Glucosamine" (just a trivial name, I know), I get the ring form (SMILES code OC1[C@H](N)[C@@H](O)[C@H](O)[C@H](O1)CO), even though 2Carb states "D-Glucosamine for 2-amino-2-deoxy-D-glucose" (https://iupac.qmul.ac.uk/2carb/14n15.html), which would be the open-chain form (OPSIN also returns the correct form for the full name, SMILES code N[C@@H](C=O)[C@@H](O)[C@H](O)[C@H](O)CO).

I could just use the full name, but I encountered other "systematic names" in the 2Carb appendix that use "Glucosamine", e.g. "Lactosamine (LacN): β-D-Galactopyranosyl-(1→4)-D-glucosamine".

[dan2097]

2Carb also states on the same page that it's equivalent to 2-Amino-2-deoxy-D-glucopyranose, which doesn't really clarify things.

In practice there is typically some amount of interconversion between the pyranose and furanose forms (via the open chain) with the pyranose form being more prevalent for most sugars. I think without explicit indication otherwise that most will assume the trivial names correspond to the most common form e.g. https://en.wikipedia.org/wiki/Glucosamine.

[JonasSchaub]

Good catch, I didn't notice this contradictory example on the same page :D

I think without explicit indication otherwise that most will assume the trivial names correspond to the most common form

Definitely, but the basis for nomenclature is usually the open-chain form, right?

[dan2097]

Definitely, but the basis for nomenclature is usually the open-chain form, right?

I think it's rather unclear. https://iupac.qmul.ac.uk/2carb/05.html#051 sort of discusses this:

Most monosaccharides exist as cyclic hemiacetals or hemiketals. Cyclic forms with a three-membered ring are called oxiroses, those with a four-membered ring oxetoses, those with a five-membered ring furanoses, with a six-membered ring pyranoses, with a seven-membered ring septanoses, with an eight-membered ring octanoses, and so on. To avoid ambiguities, the locants of the positions of ring closure may be given; the locant of the carbonyl group is always cited first, that of the hydroxy group second (for relevant examples of this see 2-Carb-6.4). Lack of ring size specification has no particular implication.

If it is to be stressed that an open-chain form of an aldose is under consideration, the prefix 'aldehydo-' may be used. For ketoses, the prefix is 'keto-'

e.g. aldehydo-glucosamine must give the open-chain form