If you want to modify an adjective that modifies a noun, the word you need is tam instead of talis.
For example, virgo tam pulchra would be "such a pretty girl".
If you use talis instead, the girl is both "pretty" and "such".
The word talis only modifies nouns directly, so it can't be used for your purpose.
φρήν, stem φρεν-, reflects a Proto-Indo-European root (straightforwardly *bʰren-, though *gʷʰren- has also been posited) in the e-grade, -φρων, stem -φρον-, has the same root in the o-grade. In both cases here the vowel is lengthened due to Szemerényi's law, a PIE sound law which holds that *-VRs > *-VːR—that is, if a vowel is followed by a resonant and ...