Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
M:3/2
K:Gmin
['cBAG ^F4', 'B4 f4 edcB A4 Bcde f2 _A2']  
X:1
L:1/8
M:3/2
K:Gmin
 d4 cBAG e2 d2 | c2 ed cBAG ^F4 | GDAD BDAD BDcD | dced cBAG ^F4 | f4 edcb g2 f2 | e2 gf edcB A4 | 
 fBgB fBgB aBbf | edcB E2 A2 B4 :: f4 edcB A4 | Bcde f2 _A2 A2 G2 | g4 fedc =B4 | 
 cdef g2 B2 B2 A2 | b4 ag^fg a2 d2 | c2 ed cBAG ^F4 | ecAc dBGB cA^FA | BGFB D2 ^F2 G4 :|  