Isaiah 43.21
Septuagint

laon mou on periepoihsamhn

New Testament - 1 Peter 2.9

laoV eiV peripoihsin

Septuagint

my people whom I have preserved

New Testament

a people for Gods own possession 

Masoretic Text

the people which I formed for myself

Comments:  On first glance, the Septuagint and the New Testament appear to disagree.  But the Greek words peripoihsamhn and peripoihsin are clearly related. Peripoihsamhn is a first person singular aorist indicative verb in the middle voice, and could be translated, I have preserved, kept safe, or procured for myself.  Peripoihsin is the accusative singular form of peripoihsiV, a keeping safe or an acquiring.  Brenton has chosen the idea of  preservation, while the ASV translators stressed acquisition.

The MT involves the notion of formation, which is absent from the NT.