New peptidomimetic inhibitors of retroviral proteases are in particular for human immunodeficiency virus (HIV) protease. These inhibitors include as the core structure a new diamiriodiol isostere of the dipeptide Phe-Pro having four stereogenic centers. The inhibitors have been shown to inhibit HIV-protease and can therefore be usefully employed as antivirals for post-exposure prophylaxis and as a therapy for viral infections by a retrovirus, in particular HIV. The syntheses processes of the isosteres and inhibitors are also described.