Construct a musical composition following the given alphabetical structure and incorporating the specified motif.
X:1
L:1/8
Q:1/8=50
M:5/8
K:F#phr
['G B2']  
X:1
L:1/8
Q:1/8=50
M:5/8
K:F#phr
"^(50 mpm)" B2 GBc | d2 dcc | B2 G B2 | BG GGB | Bc d(cB) | cB G B2 | B2 B B2 | dd Bdd | 
 (cB) G B2 | (BG) G B2 | D2 D F2 | FG G D2 | dd dfg | f2 d f2 | f2 f d2 | (dd) BBd | c2 cBG | 
 FG B(BG) | (Bc) d(cd) | e2 fge | (ef) g f2 | f2 dee | e2 =c c2 | B2 BBB | (BG) G(Bc) | (dc) BBB | 
 F2 F F2 |]  