pcre2 - Regex match to distinct letters only - regex

Question

I am trying to create a regex that matches the following criteria below
first letter is uppercase
remaining 5 letters following the first letter are lowercase
ends in ".com"
no letter repeats only before the ".com"
no digits
there are only 5 lowercase letters before the .com, with only the first letter being uppercase
The above criteria should match to strings such as:
Amipsa.com
Ipsamo.com
I created this regex below, but the regex seem to capture repeating letters - examples here: https://regex101.com/r/wwJBmc/1
^([A-Z])(?![a-z]*\1)(?:([a-z])\1(?!\2)(?:([a-z])(?![a-z]*\3)){3}|(?:([a-z])(?![a-z]*\4)){5})\.com$
Would appreciate any insight.

Answer 1

You may use this regex in PCRE with a negative lookahead:
^(?!(?i)[a-z]*([a-z])[a-z]*\1)[A-Z][a-z]{5}\.com$
Updated RegEx Demo
RegEx Details:
^: Start
(?!: Start negative lookahead
(?i): Enable ignore case modifier
[a-z]*: Match 0 or more letters
([a-z]): Match a letter and capture in group #1
[a-z]*: Match 0 or more letters
\1: Match same letter as in capture group #1
): End negative lookahead
[A-Z][a-z]{5}: Match 5 lowercase letters
\.com: Match .com
$: End

Answer 2

You might use
^(?i)[a-z]*?([a-z])[a-z]*?\1(?-i)(*SKIP)(*F)|[A-Z][a-z]{5}\.com$
Regex demo
Explanation
^ Start of string
(?i) Case insensitive match
[a-z]*?([a-z])[a-z]*?\1 Match 2 of the same chars a-z A-Z
(?-i) Turn of case insenstive
(*SKIP)(*F) Skip the match
[A-Z][a-z]{5} Match A-Z and 5 chars a-z
\.com Match .com
$ End of string
Another idea if you are using Javascript and you can not use (?i) is to use 2 patterns, 1 for checking not a repeated character with a case insensitive flag /i and 1 for the full match.
const rFullMatch = /^[A-Z][a-z]{5}\.com$/;
const rRepeatedChar = /^[a-z]*([a-z])[a-z]*\1/i;
[
"Regxas.com",
"Ipsamo.com",
"Plpaso.com",
"Amipsa.com",
"Ipsama.com",
"Ipsima.com",
"IPszma.com",
"Ipsamo&.com",
"abcdef.com"
].forEach(s => {
if (!rRepeatedChar.test(s) && rFullMatch.test(s)) {
console.log(`Match: ${s}`);
}
});