WHI-07, a novel bromo-methoxy-substituted aryl
phosphate derivative of
zidovudine (ZDV), is a potent dual-function
contraceptive agent. Although the bromo-methoxy functional groups in the
thymine ring of its ZDV are very important for its sperm-immobilizing activity (SIA), the importance of the esterification of the
phosphate group with an
amino acid side chain and the identity of the para substituent in the aryl moiety remain unclear. In the present study, we have synthesized 23 new analogues of
WHI-07 by replacing the
alanine (Ala) side chain with different
amino acids containing nonpolar side chains, namely
tryptophan (Trp),
proline (Pro),
phenylalanine (Phe),
leucine (Leu),
methionine (Met),
valine (Val), or
glycine (Gly). The para substituents on the aryl moiety included bromo, chloro, fluoro, nitro, or methoxy groups. The SIA of each of the 23
WHI-07 analogues was evaluated by computer-assisted sperm analysis. The potential cytotoxicity of these compounds against normal human ectocervical and endocervical epithelial cells was evaluated using MTT (3-[4, 5-dimethylthiazol-2-yl]-2,5-
diphenyl tetrazolium
bromide) cell viability assays. The replacement of the Ala side chain of
WHI-07 with
Val, Leu, or Phe led to a complete loss of SIA (EC(50) values > 500 microM), whereas replacement with Trp reduced the SIA by 4-fold. The presence of para substituents on the phenyl moiety led to significant alterations in SIA. The anti-human immunodeficiency virus (HIV) activity of Trp-containing
WHI-07 analogues was also diminished. Our finding highlights the necessity of Ala side chain and the presence of electron-withdrawing para-bromo substituent on the phenyl moiety in addition to bromo-methoxy functionalization groups on the
thymine ring in order for the
phosphoramidate derivatives of ZDV to be effective dual-function
spermicidal agents. Unlike the
detergent-type
microbicide,
nonoxynol-9, which was cytotoxic to normal human ectocervical and endocervical epithelial cells (IC(50) values of 22 microM and 16 microM, respectively) at spermicidal concentrations (EC(50) = 81 microM),
WHI-07 and its active analogues were selectively spermicidal without cytotoxicity against female genital tract epithelial cells.
WHI-07 and its Trp analogues hold particular clinical promise for the development of novel, nondetergent-type prophylactic
contraceptives for the prevention of heterosexual HIV/
acquired immunodeficiency syndrome transmission.