Learn Turkish: Hayırseverlere teşekkür etmek şöyle dursun, onlara karşı çok mahcubum. - Let alone thanking the philanthropists, I am very embarrassed towards them.

şöyle dursun means "let alone" or "never mind doing something". It directly follows the basic infinitive form, which is teşekkür etmek (to thank) here. You can absolutely swap it with bir yana in this sentence (teşekkür etmek bir yana) with no change in meaning. They both set up a dismissive contrast: "Forget about thanking them, I actually feel the opposite."

Why does "hayırseverler" take the dative suffix "-e" here?

In Turkish, you give your thanks to someone. The verb teşekkür etmek (to thank) always takes the dative case. So, instead of a direct object, we use hayırseverlere (to the philanthropists).

What does "karşı" do in the phrase "onlara karşı"?

karşı is a postposition meaning "towards" or "against", and it always requires the word before it to be in the dative case (hence onlara). While an English speaker might say "I am embarrassed in front of them", Turkish phrasing directs the feeling of embarrassment towards them: onlara karşı çok mahcubum.

What happened to the spelling of "mahcup" at the end of the sentence?