Da. Holt et al., STRUCTURE-ACTIVITY STUDIES OF NONMACROCYCLIC RAPAMYCIN DERIVATIVES, Bioorganic & medicinal chemistry letters, 3(10), 1993, pp. 1977-1980
X-ray crystallography suggests the C23-C28 segment of rapamycin may ac
t more as an element of the FKBP binding domain than as part of the im
munosuppressant effector domain. Selective excision of this region fro
m the natural product followed by minor reconstruction of the binding
domain resulted in compounds with high affinity for FKBP but no immuno
suppressive activity. This, along with data from other secorapamycin a
nalogs, suggest the importance of C23-C28 in the orientation of the ef
fector domain.