Stereospecific enzyme that catalyzes the NADPH-dependent reduction of (3R)-vestitone to (3R,4R)-4'-methoxyisoflavan-2',4,7-triol (DMI). Has no activity with (3S)-vestitone. Catalyzes the penultimate step in the biosynthesis of the phytoalexin medicarpin, and thereby contributes to plant defense reactions. a (3R,4R)-4,2'-dihydroxyisoflavan + NADP(+) = a (3R)-2'-hydroxyisoflavanone + H(+) + NADPH Inhibited by vestitone concentrations above 50 uM. Optimum pH is 6.0. Optimum temperature is 30 degrees Celsius. Monomer. Detected in roots, and at lower levels in root nodules. Not detected in petioles, leaf and stem. Transiently up-regulated by fungal elicitors, peaking 6 hours after elicitor treatment. Belongs to the NAD(P)-dependent epimerase/dehydratase family. Dihydroflavonol-4-reductase subfamily.