Let us see the pairs that can be considered as adjacent in Karnaugh's here.

The pairs are: 

1)  The four corners 

2)  The four 1's as in top and bottom in column 00 & 01

3)  The two 1's in the top two rows of last column.

Corners can be represented by expressions: 

1)      Four corners

2)      The four 1's in column 00 and 01 gives subsequent terms

3)      The two 1's in last columns

So Boolean expression derived from this K-Map is

F    =   B¯D¯ +B¯C¯ +A¯CD¯

Expressions so obtained by K-Maps are in forms of sum of product form it implies that it is expressed as sum of products of variables. This expression can be expressed in product of sum form however for this special method are required to be used.