使用正则表达式从句子中找到[a-zA-Z]的单词

I'm trying to get all the words in a sentence with regex but only the ones with [a-zA-Z]. So for "I am a boy" I want {"I", "am", "a", "boy"} but for "I a1m a b*y", I want {"I", "a"} because "a1m" and "b*y" includes characters other than [a-zA-Z].I'm trying to get all the words in a sentence w