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Is there a trivial name for compounds based on glutamic acid, or other amino acids, where it is not the α-amino acid group that is functionalised? (I.e. that shown on the right)

Glutamylsulfonic acid, for instance, would seem to have a structure similar to glutamyl aldehyde, but with a sulfonic acid group appended to the aldehyde. Following on from the centre-right example, dimethyl glutamate could also be named: glutamic acid 1,5-dimethyl ester.

The issue seems to be that the glutamyl- group is no longer technically present, but the compound still strongly resembles glutamic acid. I am aware that amino acids do not normally exist in these neutral forms, and am only interested in the nomenclature.

Glutamic acid, glutamyl aldehyde, glutamic acid 1-methyl ester, and (blank!)

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    $\begingroup$ I don't think even the names you came up with are OK. All this should be named systematically. $\endgroup$
    – Mithoron
    May 26, 2022 at 0:51
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    $\begingroup$ I would name the sulfonic acid as a homocysteine derivative rather than glutamate $\endgroup$
    – Andrew
    May 26, 2022 at 1:14
  • $\begingroup$ Also the aldehyde is often called glutamate semi-aldehyde to indicate that only one acid group had been reduced $\endgroup$
    – Andrew
    May 26, 2022 at 1:15
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    $\begingroup$ This one is glutamate-1-semialdehyde as opposed to glutamate-5-semialdehyde. $\endgroup$
    – Karsten
    May 26, 2022 at 1:18
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    $\begingroup$ This is not an answer to the question but the systematic names of the shown structures are (2S)-2-aminopentanedioic acid, (4S)-4-amino-5-oxopentanoic acid, (4S)-4-amino-5-methoxy-5-oxopentanoic acid, and (2S)-2-amino-4-sulfobutanoic acid. Note that the last compound does not resemble glutamic acid anymore since it has lost a C atom so it's a butanoic acid and not a pentanoic acid. $\endgroup$
    – Loong
    May 26, 2022 at 7:20

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As you're aware, biochemists typically do not use systematic naming for most compounds, preferring instead to use common names and modifying them as needed for related compounds. In the case of amino acids, the names typically are created based on the names of the proteinogenic amino acid names. I do not know of any codified formal rules for this process, but a quick look at the names in use suggests a few guidelines that seem to be followed most of the time. Here's an imcomplete summary.

1: Priority seems to be given to the "R" functional group rather than, for example, chain length. Thus, $\ce{HS-CH2-CH2-CH(-NH2)-CO2}$ is named as "homocysteine" based on the presence of the -SH group rather than as a variant of methionine, which has the same number of carbons and a sulfur atom, but not a sulfhydryl group. Similarly, $\ce{HO-CH2-CH2-CH(-NH2)-CO2}$ is named homoserine rather than considered a reduced form of aspartate, which has the same number of carbons.

2: The prefix "homo" indicates an extra methylene group in the side chain (eg homoserine, homocysteine, homolysine)

3: The prefix "nor" indicates a structural isomer of an alkyl side chain (eg norvaline, norleucine)

4: Aldehydes tend to be named as carboxylic acid derivatives rather than alcohols, so $\ce{OCH-CH2-CH(-NH2)-CO2}$ is aspartate semialdehyde rather than an oxidized homoserine.

5: The suffix -ol designates reduction of the 1-carboxylic acid group to an alcohol.

The sulfonic acid compound you asked about poses an interesting challenge, because it does not have a methyl group on the S, but also is not an -SH group. One could make an argument for naming this compound as either a methionine or homocysteine derivative, but convention seems to favor homocysteine, based on similar compounds such as S-adenosyl homocysteine. Thus it would be "homocysteine sulfonic acid".

As noted in the comments, your aldehyde compound is typically named glutamate-1-semialdehdye to indicate that only one acid group (at the 1 position) is reduced.

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  • $\begingroup$ Contradiction to "rule 1": Why glutamic acid is not named homoaspartic acid? :-) $\endgroup$ May 26, 2022 at 16:24
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    $\begingroup$ @MathewMahindaratne It's a proteinogenic amino acid, so it gets its own name. The prefixes are for variants of the proteinogenic amino acids $\endgroup$
    – Andrew
    May 26, 2022 at 18:05
  • $\begingroup$ I understood but wonder why not. I gave my upvote nonetheless. $\endgroup$ May 26, 2022 at 18:16

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