How can I match first letters and also if the letter is precedded by period, comma or colon (even with no space between), but not if the letter is preceded by a quote or dubble quote.

Lookbehind is not supported by JavaScript. (tried /\b(?<!\'|\")[\w]/g with syntax error). Any replacement method?

Ex: abcd e'fgh hj"kl mno.p q:rst uv,wx
The match should be a,e,h,m,p,q,q,r,u,w (excluding f,k)