(S) O (R) (S) (R) (S) (S) O (R) (R) (R) (R) (R) O H 3 C CH 3 (S) (R) O OH HO H 3 C (R) O CH 3 (S) (S) (R) (R) O H 3 C O CH 3 O H 3 C HO N CH 3 CH 3 O CH 3 O H 3 C CH 3 CH 3 CH 3 CH 3