Nothing US friend turned up in the capital (6)
I believe the answer is:
dublin
'capital' is the definition.
(capital of Ireland)
'nothing us friend turned up' is the wordplay.
'nothing' becomes 'nil' (eg nil is zero in football).
'us friend' becomes 'bud' (US term for a friend).
'turned up' is a reversal indicator.
'nil'+'bud'='nilbud'
'nilbud' back-to-front is 'DUBLIN'.
'in the' acts as a link.
(Other definitions for dublin that I've seen before include "European city" , "City of 1 across" , "Capital of Ireland" , "Ulysses city (Joyce)" , "Capital of Eire" .)