Aspartylphenylalanine methyl ester derivative was synthesized by photoalkylation reaction of N-X-glycylphenylalanine methyl ester (X=trifluoroacetyl or acetyl) with acetic anhydride as an alkylating agent. The reaction was induced with 350nm lamp utilizing a mixture of diacetyl(DA) and di-t-butyl peroxide (DBP) as a photoinitiator. When acetone/DBP was used as a photoinitiator under the same conditions, no photoalkylation was observed.
The progress of the reaction was followed with analysis of the amino acid compositions of the irradiated dipeptide. After hydrolysis of the irradiated sample, each amino acid was identified by the comparison with authentic samples on this layer chromatogram. When the reaction was induced by the mixture of DA and DBP, a new amino acid, aspartic acid, could be detected indicating the successful photoalkylation reaction as planned.
When a mixture of N-trifluoroacetyl-glycyphenylalanine methyl ester and acetic anhydride with DBP as a initiator was heated at 120℃ - 130℃ for about 50 hrs in a sealed ampule, the same alkylation was induced at glycine residue very likely through free radical mechanism. In comparison with this thermal alkylation reaction, the photoalkylation reaction is also thought to undergo via a free radical mechanism.
N-X-glycylphenylalanine methyl ester (X = trifluoro acetyl 또는 dicetyl) 와, acetic anhydride 를 알킬화제로 사용하여 광화학 반응을 일으키면 글리신잔기는 aspartic acid 의 유도체로 전환된다. 이 반응은 광개시제로 diacetyl (DA) 와 di-t-butyl peroxide(DBP) 를 사용하였고 광원으로 파장이 350 nm인 램프를 사용하였다. 아세톤 또는/DBP 를 사용했을 때는 같은 조건하에서 반응이 일어나지 않았다.
반응의 진행여부는 빛을 쪼인 디펩티드의 아미노산 분석을 통하여 확인하였다. 빛을 쪼인 디펩티드를 가수분해 한 후 아미노산의 조성을 표준시료와 함께 thin layer chromatograph 법에 의해 비교 하였다. DA 와 DBP 의 혼합물로 반응을 일으킨 경우에는 계획한 대로 성공적인 알킬화 반응이 일어났음을 나타내는 새로운 아미노산의 aspartic acid 를 검출할 수 있었다.
N-trifluoroacetyl glycylphenylalanine methyl ester, anhydride 와 DBP 를 개시제로 사용하여 밀폐된 ampule 에서 120 - 130℃ 로 50시간 가열한 결과 자유 라디칼 반응을 거쳐 일어나는 같은 알킬화 반응이 글리신 잔기에 일어났다. 이 열알킬화 반응과 비교하면 광알킬화 반응도 자유 라디칼 메카니즘에 의해 일어날 것으로 추축된다.
