To gain an insight into possible cage/spacer combinations, we selected compounds of the cubic D4R type, [2,6-(i-Pr)2C6H3(Me3Si)NSi(O)3Ti(O-i-Pr)]4 (1), [Me2NAl(O)3P-t-Bu]4 (2), and [XAl(O)3PR]4 (3, X = Me, i-Bu, R = t-Bu, c-Hex), and studied the reactivity of their amido, alkoxo, and alkyl substituents with a series of protic reagents. Alcohols, silanols, phenols, and acids with different acidity and steric bulkiness were employed. While the dimethylamido groups in 2 are easily replaced, the bulky and less basic aryl(trimethylsilyl)amido groups in 1 resist substitution. Instead, the alkoxy groups in 1 are exchanged or the whole framework is destroyed in the reactions with strongly acidic reagents. A new model compound for the structural moiety P(OSi)1(OAl)3 found in silicoaluminophosphates (SAPO) was prepared by a dealkysilylation reaction of alumazene [2,6-(i-Pr)2C6H3NAlMe]3 with tris(trimethylsilyl)ester of phosphoric acid. The resulting (MeAl)[2,6-(i-Pr)2C6H3N]3{Al[OP(OSiMe3)3]}2(O3POSiMe3) (4) contains a heteroadamantane core and was characterized by analytical and spectroscopic methods and its molecular structure was established by a single crystal X-ray diffraction experiment. This new aluminophosphate could serve as the starting point for developing other structural units as it contains reactive groups.